Quality_And_Function.. - American Palm Oil Council
Quality_And_Function.. - American Palm Oil Council
Quality_And_Function.. - American Palm Oil Council
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Published by<br />
MALAYSIAN PALM OIL COUNCIL<br />
2nd Floor, Wisma Sawit Lot 6, SS6, Jalan Perbandaran,<br />
47301 Kelana Jaya, Selangor, Malaysia.<br />
Copyright © 2010 Kurt G. Berger<br />
All rights reserved. No part of this book may be reproduced in any form or by any means<br />
without prior permission from the Publisher.<br />
National Library of Malaysia<br />
Cataloguing-In-Publication Data<br />
Berger, Kurt G.<br />
<strong>Quality</strong> and functions of palm oil in food applications: a layman's guide/ Kurt G. Berger<br />
ISBN 978-983-9191-09-7<br />
I. <strong>Palm</strong> oil -- <strong>Quality</strong>. 2. <strong>Palm</strong> oil--By product. 3. <strong>Palm</strong> Products--Malaysia<br />
I.Title<br />
633.85109595
FOREWORD<br />
While working at the <strong>Palm</strong> <strong>Oil</strong><br />
Research Institute of Malaysia (now the<br />
Malaysian <strong>Palm</strong> <strong>Oil</strong> Board) in the 1980s<br />
I received a phone call from a social<br />
acquaintance involved in the palm oil<br />
trade, asking "I say old chap, what's a<br />
fatty acid then?" It was not difficult to<br />
help him.<br />
Reflecting on the question later it<br />
occurred to me that many of the people<br />
involved in palm oil, from growing through to end use, would surely find it interesting<br />
and of benefit to know something of the basic technology.<br />
That thought led to a series of articles in the Global <strong>Oil</strong>s & Fats Business Magazine<br />
(GOFB). There were two main objectives.The first was to describe the parameters used<br />
to judge the quality of the product and the measures needed to ensure its good arrival<br />
at the user, and the second was to provide information on how it is used in food production<br />
around the world and, with it, to give some insight into the fascinating scientific<br />
aspects of food.<br />
My own involvement in palm oil dates back to my time in the London research laboratories<br />
of a large food manufacturer. In 1953 the British food industry was finally liberated from<br />
the shackles of the wartime Food Ministry control, and we started to experiment with<br />
palm oil, which was a new ingredient to us.We found that it was functional and economic<br />
in a number of our products.<br />
This work led 20 years later to an invitation to talk about our experience at a two-day conference<br />
in London dealing with palm oil from the planting to the eating. One of the other<br />
speakers was Tan Sri Borg Bek-Nielsen. When we met again in 1976 he remembered my<br />
presentation and said: "We are thinking of starting a Research Institute for palm oil and you<br />
must come and help us when we are ready."
Two years later a formal invitation came, which I was able to accept. There followed an<br />
exciting and busy eight years in Malaysia. First we needed to draft a research programme<br />
and agree it with the technical committee of the industry; next, to establish temporary laboratories,<br />
for which we found two shophouses in the suburbs of Kuala Lumpur; and then<br />
came the planning of permanent buildings and selection of a site for the Institute.<br />
Chemical research started in 1979 and within two years yielded results that were suitable<br />
for presenting at an international palm oil conference organised by the Incorporated<br />
Society of Planters.<br />
Staff for the Technical Advisory Service were recruited in 1980 and soon started to investigate<br />
the potential uses of palm oil around the world, feeding back to the Food Technology<br />
Unit any problems that needed practical investigation. It was important to publicise useful<br />
results at international conferences and to take part in government-led trade missions.<br />
Not surprisingly perhaps, we found people who were suspicious of an ingredient unknown<br />
to them after using only their traditional ingredients for many years.At that time, only western<br />
Europe was knowledgeable about palm oil.To develop some confidence in the product,<br />
a Familiarisation Programme was instituted; key people in government offices and<br />
industry in developing countries were invited at the Institute's expense to visit Malaysia for<br />
two weeks.They were shown the plantations, the refineries and the work of the research<br />
institute and given opportunities to talk to all those concerned.<br />
This programme continues today, and there is no doubt that the friendly contacts made<br />
have oiled the wheels of commerce. It proved particularly useful in a number of countries<br />
where purchasing decisions were made in government offices with little technical knowhow.<br />
It is similarly urgent today to inform present and potential importers of palm oil's versatility<br />
in application in their accustomed food products.This book is based on the GOFB series<br />
of articles, edited and brought up to date.<br />
Kurt Berger<br />
Food Technology Consultant, UK
CONTENTS<br />
CHAPTER 1<br />
Basic chemistry of fats<br />
CHAPTER 2<br />
Tests of quality<br />
CHAPTER 3<br />
<strong>Quality</strong> during transport<br />
CHAPTER 4<br />
Bakery products<br />
CHAPTER 5<br />
Aerated dairy products<br />
CHAPTER 6<br />
Butter alternatives<br />
CHAPTER 7<br />
The lauric oils<br />
CHAPTER 8<br />
Confectionery fats<br />
CHAPTER 9<br />
Frying oils<br />
CHAPTER 10<br />
Low trans fats formulae<br />
CHAPTER 11<br />
<strong>Palm</strong>-based oleochemicals<br />
CHAPTER 12<br />
<strong>Oil</strong>s and fats properties<br />
8<br />
14<br />
21<br />
29<br />
39<br />
46<br />
65<br />
70<br />
79<br />
87<br />
93<br />
106
8<br />
CHAPTER 1: BASIC CHEMISTRY OF FATS<br />
Technical aspects of oils and fats are of importance to those in the business.This chapter<br />
examines the chemical composition of oils and fats.<br />
Nine propositions cover the basic chemical information required to understand the main<br />
technical terms used in the oils and fats industry (see Box).
9<br />
PHYSICAL PROPERTIES<br />
What makes fats solid and oils liquid? More details about fatty acids are useful in answering<br />
this. At first sight, one would think that a double bond would be stronger than a single<br />
one in linking the Carbon chain. However, the two bonds involved are bent out of their natural<br />
position and therefore are under strain. So, a double bond is actually weaker.
10<br />
So triglycerides containing only or mainly straight saturated acids align easily together to form<br />
crystals. Such triglycerides are solid at room temperature.The kink in the unsaturated acids<br />
makes it more difficult for their triglycerides to align and form crystals, so they stay liquid.<br />
Most of the major vegetable oils contain mainly unsaturated fatty acids and are liquid at<br />
room temperature.These consist of soybean, rapeseed, sunflower, cottonseed, groundnut,<br />
olive and maize oils.<br />
The most important exception is palm oil.With 50% unsaturated and 50% saturated acids, it<br />
has a solid consistency at room temperature and is therefore unusual among vegetable oils.<br />
Coconut and palm kernel oils are also solid due to their unusual content of short and medium<br />
chain saturated acids. They have special applications in food and in the oleochemical<br />
industry. In terms of world supply, they are available in relatively small amounts.<br />
FOOD USES<br />
Many of the food uses of oils and fats depend on the consistency or body. A simple example<br />
- you can't pour margarine or butter on salad, and you can't spread olive oil on bread.<br />
A solid character to a varying degree is necessary in fats for margarine, for bakery products,<br />
for ice cream. Historically, this solid character was provided by animal fats, but these<br />
are little used in margarine and bakery fats nowadays.<br />
The liquid oils can be modified to have a solid consistency by hydrogenation. Hydrogen is<br />
added to some of the unsaturated component fatty acids, so increasing the average saturation<br />
of the oil. The process takes place at around 100°C when the oil is mixed with<br />
hydrogen gas in the presence of a catalyst. This sounds very simple but at the molecular<br />
level there is a complication.<br />
During hydrogenation the unsaturated acid has to go through an intermediate stage. At<br />
this point the kink at the double bond is ironed out, the chain becomes straight but the<br />
double bond is still there. It is now a 'trans' unsaturated fatty acid (trans fat). Partly-hydrogenated<br />
oils always contain a mixture of saturated acids, unchanged unsaturated acids and<br />
trans fats.<br />
Trans fats are now known to be nutritionally undesirable, since research has shown that<br />
they raise the level in the blood of undesirable 'LDL cholesterol' which is involved in the
11<br />
process of clogging up the arteries. At the same time they also decrease the blood level of<br />
the desirable 'HDL cholesterol' which removes excess cholesterol from the blood stream.<br />
This doubly adverse result is now universally recognised and has led national and international<br />
expert bodies to advise minimising trans fats in foods.<br />
Some countries have labelling laws to declare the trans fats content in food products.<br />
Denmark has imposed a legal limit on the amount. Consumer awareness of nutritional<br />
issues is high everywhere and food industry management is therefore strongly motivated<br />
to remove trans fats from products. In the UK a large supermarket is stating that most of<br />
its products are now free of trans fats, and the rest are following.<br />
Two approaches are used to make consistent fats without trans fats:<br />
1. If you completely hydrogenate liquid oil, so that all double bonds are saturated, clearly<br />
you no longer have any trans fats. However, such a fat is as hard as bricks and, on its own,<br />
of no use in food.<br />
Another simple chemical process, 'interesterification' comes into play.The fully saturated<br />
fat is melted and mixed with liquid oil.A catalyst is added, which induces all the fatty acids<br />
to disconnect from their glycerol and re-attach to some other available glycerol in a random<br />
manner. If you get the right proportions of the ingredients, you finish with a fat of<br />
just the desired consistency.<br />
2. The second approach uses palm oil or its higher melting fraction, palm stearin, either in<br />
a mixture with other oils, or by using the interesterification procedure on a mixture<br />
designed to get the characteristics needed.<br />
The choice between the two approaches will depend on circumstances; for example, the<br />
availability of locally produced oils may point to the first method. In many situations the<br />
palm oil method is the more economic, as in the USA.<br />
The steady increase in recent USA imports (Figure 1) shows that some manufacturers<br />
have been taking advantage of the 'solid fat' properties of palm oil and palm stearin<br />
since 2000. This trend can confidently be predicted to continue. Some commercial<br />
firms in the USA already offer palm-based products for formulations that are free of<br />
trans fats.
12<br />
Interchangeable use<br />
A degree of interchangeability of oils is welcomed by the food industry as it gives the buyer<br />
a choice of the cheaper supply. But just how interchangeable are vegetable oils? This answer<br />
very much depends on the intended use.<br />
For example, when selecting the solid component for a margarine formula, it was possible<br />
to choose between partly hydrogenated soybean, rapeseed or other liquid oil and palm oil.<br />
Today this option is much less available due to marketing considerations; palm oil is therefore<br />
a unique ingredient for this purpose.
13<br />
For use as a salad oil it is desirable that the oil should remain clear at the temperature of<br />
a domestic refrigerator (5°C or 40°F).This criterion is met by soybean, rapeseed, olive and<br />
sunflower oils. It is also met by maize oil, provided its traces of natural waxes have been<br />
removed. So, all these oils can be regarded as interchangeable. Both groundnut and cottonseed<br />
oil tend to crystallise in the refrigerator, as does palm olein, which is the more liquid<br />
fraction of palm oil.<br />
While the above salad oils are interchangeable as regards technical performance, there are<br />
still aspects of consumer choice.Thus olive oil is often prized for its special flavour characteristics<br />
and commands a high price.There may be a preference for sunflower oil or maize<br />
oil because they have long been promoted as being healthy, due to their high content of<br />
the nutritionally essential linoleic acid.<br />
Use in frying<br />
The important use of oils and especially palm oil for frying will be discussed in Chapter 9.<br />
At present, interchangeability of oils is limited in deep frying.This is likely to change in the<br />
future due to the efforts of plant breeders. They are succeeding in producing oils with<br />
reduced levels of the more unsaturated acids.<br />
Extensive full-scale trials with a 'high oleic' sunflower oil (and low in linoleic acid) have<br />
proved its good performance in potato crisps. Rapeseed and soybean oils of modified composition<br />
suitable for frying are now available in limited quantity.<br />
Some snack food operations have already changed from palm olein to the high oleic sunflower<br />
oil despite its significantly higher price.This demonstrates the dynamic nature of the<br />
competition between the different oils and of their interchangeability.<br />
The reason for the decision to change is the perception that the more unsaturated sunflower<br />
oil is healthier. It is clearly important for the long term that research into creating a<br />
palm oil low in saturates and high in unsaturates should be successful.<br />
To take full advantage of the productivity of the oil palm, the world market has a clear<br />
demand for two types of palm oil - firstly, the present type of palm oil, so valuable in the<br />
production of consistent fats; but secondly an unsatisfied demand for a palm oil that is truly<br />
competitive in its characteristics with the liquid vegetable oils.
14<br />
CHAPTER 2: TESTS OF QUALITY<br />
Chapter 1 explained the chemistry of oils and fats, how this affects their use in foods, and<br />
why the special characteristics of palm oil are valued.<br />
In this chapter, we look at how the quality of vegetable oil is analysed – how quality of oil<br />
is defined at the time of purchase in global trade, in view of the need to protect against<br />
deliberate or accidental adulteration.<br />
It describes how analysis methods are standardised and applied in determining ‘quality’,<br />
which the dictionary defines as:<br />
a. An inherent or distinguishing characteristic, a property; essential character or nature<br />
b. Superiority of kind, degree or grade of excellence<br />
In practical terms, is the oil what it is supposed to be and is it in good condition? Both these<br />
aspects are defined by means of chemical analyses. For credibility, these must be carried out<br />
by qualified analysts using standardised procedures.<br />
STANDARD METHODS OF ANALYSIS<br />
The process of standardisation is elaborate and is organised by national bodies such as the<br />
British Standards Institute or <strong>American</strong> <strong>Oil</strong> Chemists Society, or international bodies like the<br />
International Union of Pure and Applied Chemistry, International Standards Organisation,<br />
or the Codex Alimentarius Commission set up under the United Nations.<br />
A number of reputable laboratories volunteer to take part in the study of a method. A<br />
‘recipe’ is circulated together with appropriate samples and the results are analysed statistically.<br />
If not within acceptable limits of agreement, the details of the ‘recipe’ are discussed,<br />
modified and further tests arranged. Eventually acceptable results are obtained and the<br />
agreed method is given official status.<br />
The Codex commission’s objectives are to agree on codes of practice and standards for<br />
food commodities in order to facilitate international trade. Technical committees develop<br />
the standards which are adopted at government level. Over 100 nations collaborate in the<br />
Codex system and its standards carry a great deal of weight in commerce. Codex stan-
dards deal with products in consumable condition and, therefore, mainly with refined oils.<br />
Olive oil is an exception, since it is mainly used for direct consumption as crude oil.<br />
15<br />
CHEMICAL AND PHYSICAL DEFINITIONS OF IDENTITY<br />
Source of oil<br />
The first thing is to define the source of the oil. For example, soybean oil is derived from<br />
seeds of the soybean (Glycine max); olive oil from the fruit flesh of the tree Olea europea,<br />
and palm oil from the fruit flesh of Elaeis guineensis. Olive oil and palm oil are the only<br />
major vegetable oils derived from fruit flesh. All others are extracted from seeds.<br />
Iodine number<br />
All oils contain a mixture of fatty acids, both saturated and unsaturated.The proportion of<br />
unsaturated acids is a useful identity characteristic.The total number of unsaturated bonds<br />
is readily measured by the Iodine Value – literally the number of grams of iodine needed to<br />
react with the double bonds in 100gm of oil.<br />
Being natural products, oils show some variation due to variety and growing conditions.<br />
However, a range of Iodine Values normal for each oil can be established. For example,<br />
Codex gives these ranges for three oils:<br />
The <strong>Palm</strong> <strong>Oil</strong> Refiners Association of Malaysia (PORAM) has adopted the range for palm<br />
oil products in its standard specifications.<br />
Slip melting point<br />
The melting point is a useful measure of the physical properties of oil. Fats are mixtures of<br />
different glycerides, so they melt over a range of temperatures. A conventional method of<br />
obtaining a clear-cut result is used. The ‘slip melting point’ is obtained by filling a capillary<br />
tube with the sample in liquid form, crystallising it under precise cooling conditions, and
16<br />
then determining the point at which the sample rises in the tube when heated in a waterbath.The<br />
sample is not completely molten but a precise reproducible figure is obtained.<br />
• For palm oil, extensive surveys by the <strong>Palm</strong> <strong>Oil</strong> Research Institute of Malaysia (now the<br />
Malaysian <strong>Palm</strong> <strong>Oil</strong> Board) have established a range of 33-39°C, also used in PORAM<br />
trading specifications.<br />
• PORAM and Codex have adopted a slip melting point of 24°C or less for palm olein,<br />
and 44°C or more for palm stearin. Codex also gives a point of 19.5°C or less for palm<br />
super olein.<br />
Composition of oils<br />
Table 1 gives compositional data obtained by gas chromatography for typical samples of<br />
palm oil and its fractions, as well as for soybean and olive oils. For simplicity only the main<br />
fatty acid components are specified.<br />
Chromatographic methods are also useful for analysing the minor components of oils. In<br />
the Vitamin E group of substances (tocols), these consist of saturated tocopherols and<br />
unsaturated tocotrienols (Table 2).<br />
Sterol composition of oils also reveals differences useful for identification (Table 3).
17<br />
CRUDE PALM OIL (CPO) QUALITY<br />
Different tests are needed to determine the condition of oils. Until the development of<br />
Malaysian refining capacity, palm oil was mainly traded internationally as crude oil. Basic quality<br />
specifications of free fatty acids (ffa, maximum 5%) and moisture and impurities (maximum<br />
0.25%) were adopted and are still used today for standard CPO.<br />
The 5% ffa limit for standard CPO is higher than would be acceptable for other vegetable<br />
oils.This is because the palm fruit contains a very active lipase (fat splitting) enzyme, which<br />
rapidly breaks down the triglycerides to a mixture of ffa, monoglycerides and diglycerides.<br />
The enzyme is released from the fruit cells when the fruit is over-ripe or when it is bruised.
18<br />
In practice, the 1,000 or more fruitlets in a bunch do not all ripen simultaneously, so<br />
it is likely that some will be over-ripe during harvesting; others will be bruised as the<br />
bunch falls, and the lipase then becomes active. Further bruising takes place in the various<br />
operations before the bunch is sterilised and the lipase is destroyed. If fresh fruit<br />
is taken directly to the laboratory from the field, cooked and pressed immediately it<br />
is possible to obtain oil with only 0.8% ffa, but this is not practicable on a manufacturing<br />
scale.<br />
However, a special quality crude oil is offered by some producers. It is obtained by harvesting<br />
somewhat early to minimise over-ripe fruit. Since oil synthesis in the fruit is very active<br />
towards the end of ripening, some loss of yield results. Bruising during transport is avoided<br />
by taking steriliser cages to the field for loading and sterilisation is carried out without delay.<br />
<strong>Oil</strong> with a maximum ffa of 2.5% and minimal oxidation is produced and is easier to refine.<br />
Moreover, lower ffa means also a lower content of mono- and di-glycerides which can<br />
cause difficulty in fractionation.<br />
Bleachability test<br />
A pale near-white colour is regarded as an important characteristic of well-refined oil.The<br />
bleachability of CPO in the refining process is largely determined by the extent of oxidation,<br />
which leads to the formation of persistent coloured products.<br />
European refiners use an empirically standardised bleaching test in the laboratory to estimate<br />
the bleachability of CPO. Malaysian refiners have adopted a more science-based<br />
procedure developed by PORIM, known as the Deterioration of Bleachability Index<br />
(DOBI).<br />
The DOBI test involves the measurement of the absorption of ultraviolet light by a solution<br />
of the oil at two different wavelengths:<br />
• One (A) is a measure of the unchanged carotene present (carotene is easily destroyed<br />
by oxygen).<br />
• The other (B) measures the concentration of certain oxidation products of the fatty acids.
The ratio of A to B is a sensitive indicator of the extent of oxidation. PORAM has adopted<br />
a minimum level of 2.30 as a standard.<br />
19<br />
Test for oxidation<br />
Two measures of the oxidation level in crude oil are commonly used – Peroxide Value and<br />
Anisidine Value.<br />
The peroxide value is a direct measure of the amount of oxygen that has combined<br />
at the double bonds of the fatty acids. In time these oxidised bonds are<br />
broken, resulting in short chain volatile compounds and residues of oxidised glycerides.<br />
These residues are measured by the Anisidine Value. A high figure is an<br />
indication that oxidation has taken place in the past, and there has been a loss of<br />
quality.<br />
The two are sometimes combined – 2 x Peroxide + 1 x Anisidine is defined as the Totox<br />
Value. While convenient, it entails some loss of information.<br />
The full specifications for special quality CPO are given in Box 1.<br />
REFINED PALM OIL QUALITY<br />
Fully refined palm olein and palm oil are the main exports today. The PORAM trading specifications<br />
for refined palm oil are shown in Box 2.
20<br />
The Codex Alimentarius has extensive specifications (Box 3), common to all vegetable oils<br />
traded as refined oils. Each figure represents the maximum specification.
21<br />
CHAPTER 3: QUALITY DURING TRANSPORT<br />
No commodity is improved by transport.The best that can be expected is that it should<br />
arrive in unchanged condition.<br />
Edible oils can suffer during transport in three ways:<br />
• Oxidation through contact with air, particularly at higher temperatures<br />
• Hydrolysis through the action of traces of water, catalysed by acidity or by enzymic<br />
action from microbiological contaminants such as moulds or yeasts<br />
• Foreign matter such as dirt or residues from previous cargoes<br />
Most of the major vegetable oils are transported as crude oils at ambient temperature.<br />
Malaysian palm oil is mainly transported in fully refined form. It needs to be kept warm to<br />
prevent excessive crystallisation. Any loss of quality has to be rectified by a second refinery<br />
treatment resulting in extra costs to the purchaser. Any chemical changes will occur faster<br />
at temperatures above ambient.<br />
In its early years, the <strong>Palm</strong> <strong>Oil</strong> Research Institute of Malaysia (PORIM, now the Malaysian<br />
<strong>Palm</strong> <strong>Oil</strong> Board or MPOB) collected information on the extent and causes of quality<br />
changes during transport.The transport chain usually involves a number of steps.
22<br />
In some ports, unloading also involves the use of barges. At each stage the transfer involves<br />
pumps,pipelines and tanks where contamination by previous cargoes or foreign matter can occur.<br />
Each stage of the transport chain is under different management. In order to provide an<br />
assurance of good practice, independent surveyors are employed to approve the condition<br />
of the various facilities.<br />
PORIM undertook to obtain first-hand information by sampling and analysing oil at various<br />
stages of transport. Some results are summarised in Tables 1 to 3.<br />
The shipment to New Zealand (Table 1) arrived in unchanged condition.The Pakistan shipment<br />
showed some increase in acidity.The South Korea shipment showed appreciable oxidation<br />
which had occurred partly during the journey and further during transfer by barge<br />
at the port of arrival.<br />
Samples were taken from several ships’ tanks during a voyage and analysed on board (Table<br />
2). Measurements were made of the level of oxygen dissolved in the oil and of the peroxide<br />
value.
23<br />
The high iron content in the crude palm oil stearin catalysed oxidation of the oil, so that<br />
the dissolved oxygen was nearly all used up and oxidation was appreciable. The refined<br />
stearin had much lower iron content, and oxidation was quite moderate. A substantial proportion<br />
of oxygen remained in solution.<br />
Samples were drawn from a pipeline delivering oil into a shore tank at a foreign destination<br />
(Table 3).<br />
Clearly the pipeline was not clean, but contained some water and a quantity of some<br />
strongly coloured oil. From the rate of pumping it was calculated that the first 30-40 tonnes<br />
of product were sub-standard.<br />
As explained in Chapter 2, fully refined oil is expected to have a free fatty acid (ffa)<br />
content below 0.10%. Evidence from a number of shipments has shown that it is a<br />
case of the ‘the lower the better’. A follow-up study of 20 shipments showed that<br />
when the acidity was 0.05 or less at loading, then 75% landed with ffa below 0.10%.<br />
If the initial ffa was 0.05-0.10% (still within acceptable limits), only 20% landed with ffa<br />
below 0.10%.<br />
Inspection of some ships showed wide variation in conditions, from clean tanks with a perfect<br />
protective coating to those showing somewhat rusty surfaces. However clean the latter<br />
are, they catalyse oxidation reactions.<br />
The overall conclusion was that the effect of transport varied, with significant effects on oil<br />
quality in some instances.
24<br />
PREVENTING LOSS OF QUALITY<br />
<strong>Quality</strong> loss during transport is avoidable provided that exceptional care is taken in the<br />
cleanliness and condition of the equipment, and that access to the air is prevented.The latter<br />
requires the provision of nitrogen gas throughout the transport chain from the refinery<br />
to destination.<br />
Storage tanks and ships’ tanks are flushed with nitrogen before being filled, and a nitrogen<br />
atmosphere is maintained in the headspace above the oil. Gas is ‘sparged’ into the oil as it<br />
is pumped through pipelines.This involves fitting an inlet tube so that nitrogen is forced into<br />
the oil under pressure. Excellent results can be achieved, as seen in the examples in Tables<br />
4 and 5.<br />
Clearly nitrogen-blanketing largely prevented oxidation, but it also prevented any<br />
increase in acidity.This is because the ‘sparging’ removes some of the low level of water<br />
dissolved in the oil (no more than about 0.1%), which otherwise promotes some<br />
hydrolysis.<br />
Arrival of oils in perfect condition can be achieved, especially if the cargo is protected by<br />
nitrogen throughout. However, nitrogen use involves extra costs and this has prevented its<br />
use for the majority of cargoes. Still, the costs can be at least partly offset by avoiding any
25<br />
reprocessing to clean up the oil. At present only small quantities of oil are shipped with<br />
nitrogen protection. The reputation of Malaysian palm oil is enhanced when such quality<br />
maintenance is achieved, and the adoption of this handling procedure could form the basis<br />
of a brand image that could not at present be matched elsewhere.<br />
For speciality products shipped in smaller quantities, ISO tank containers may be used.<br />
These are stainless steel tanks conforming to specifications laid down by the International<br />
Standards Organisation (ISO).They hold about 21 tonnes of oil, have external heating coils,<br />
top and bottom discharge points and are easily cleaned.Their use is more expensive, but<br />
the likelihood of deterioration of the cargo is reduced.<br />
SHIPPING CONTRACTS<br />
The quality of Malaysian palm oil intended for export is controlled by government regulations<br />
and monitored by the MPOB. Issues of quality are at the forefront of shipping contracts<br />
and are dealt with in government and international regulations.<br />
The Federation of <strong>Oil</strong>s, Seeds and Fats Associations (FOSFA), based in London, prepares<br />
formal shipping contracts. Clauses relate to the quality and specification of the oil and the<br />
responsibility for cleanliness of the ship’s tank. The ship’s surveyor and the analytical<br />
chemists are expected to be members of FOSFA.The ship’s master is required to complete<br />
a certificate regarding the suitability of the tank, heating system and pipelines and<br />
the cleaning procedures used. The three previous cargoes carried in the tank must be<br />
specified.<br />
The surveyor in turn completes a certificate of the cleanliness and suitability of the ship’s<br />
tank. Loading and discharge procedures and the method of sampling for analysis are also<br />
laid down. FOSFA provides training courses for the junior and middle management of surveying<br />
companies.<br />
The FOSFA operating procedures emphasise the control of temperatures of the<br />
cargo.This is of particular importance for palm oil products. At ambient temperature,<br />
palm oil would set solid and become virtually impossible to unload. However, to keep<br />
it totally liquid, a temperature would be required which would risk a serious level of<br />
oxidation.
26<br />
FOSFA requires the temperature to be controlled according to minimum and maximum<br />
limits laid down by the International Association of Seed Crushers. Some crystallisation<br />
occurs during the voyage, and controlled reheating is therefore applied some time before<br />
discharge to raise the temperature by no more than 5°C/day, so that the oil arrives in a<br />
homogenous liquid condition.<br />
It is the surveyor’s responsibility to check that this condition has been reached at the time<br />
of arrival and sampling. In the past, disputes have arisen due to inadequate reheating. In consequence,<br />
the palm oil had partially fractionated into olein and stearin, and there were variations<br />
in composition of the oil throughout the tank.<br />
In the USA, the National Institute of <strong>Oil</strong>seed Products (NIOP) carries out functions similar<br />
to those of FOSFA. It prepares contracts, and its trading rules contain detailed requirements<br />
regarding the quality of the shipping operations.<br />
FOSFA also has recommendations for the handling temperatures for palm oil and palm kernel<br />
oil products. Substantially, the same temperatures are advised by Codex Alimentarius<br />
(Table 6).<br />
The <strong>Palm</strong> <strong>Oil</strong> Refiners Association of Malaysia has a shipping contract for processed palm<br />
oil, which is frequently used.The latest revision in 2002 uses the oil specification shown in<br />
Chapter 2. Other items relating to quality are essentially the same as those given in the<br />
FOSFA contract.
27<br />
CODE OF PRACTICE<br />
The quality aspects of transport were discussed at an international oils and fats technical<br />
conference in 1982. As a result a number of large industrial firms and some surveyors’<br />
organisations collaborated with PORIM in preparing an advisory booklet on transport. It<br />
covered design of pipework, tanks and heating systems, and operating procedures.<br />
As a further step, the Codex Alimentarius Committee on oils and fats was requested to<br />
put a Code of Practice for storage and transport into its programme of work.The advisory<br />
booklet was used as a starting point.<br />
The question of possible contamination by previous cargoes required detailed study. Most<br />
vegetable oil transport is from east to west, and ships carry a variety of chemical cargoes<br />
on the return trip. Contamination of edible oils with traces of previous cargoes is undesirable<br />
and may be dangerous.<br />
Discussion in the Codex Committee identified a number of questions to be answered, including:<br />
a. which cargoes are toxic;<br />
b. which products can be removed during a clean-up process of the oil;<br />
c. which products are absorbed by the tank coatings and how can they be removed; and<br />
d. what analytical methods are to be used.<br />
FOSFA was asked to co-ordinate the extensive work programme required to provide<br />
answers.<br />
Document CAC/RCP 36 entitled ‘Recommended International Code of Practice for the<br />
Storage and Transport of Edible <strong>Oil</strong>s and Fats in Bulk’ was issued by Codex in 1987 and most<br />
recently revised in 2005. It covers the design and operation of the facilities involved in the<br />
transport chain. An important recommendation is that the condition of the equipment<br />
involved in every transfer of the oil should be inspected by a qualified superintendent.<br />
Previous cargoes<br />
On the question of previous cargoes, it advised that the three previous cargoes carried in<br />
a ship’s tank should be declared. Previous immediate cargoes are divided into those that<br />
are banned and those that are acceptable. FOSFA adopts a similar ruling.
28<br />
The NIOP rule is different. It only lists acceptable prior cargoes. A limited list is permitted<br />
prior to the shipment of edible oil that may or may not be reprocessed before use, while<br />
a somewhat longer list is allowed for oils that are intended for reprocessing.<br />
These lists continue to be reviewed as necessary.<br />
The European Community (EC) has also adopted a positive list of acceptable previous cargoes,<br />
but believes that a negative list of banned immediate previous cargoes can cause confusion<br />
in administering the system.<br />
<strong>Oil</strong>s that are not to be further processed must be carried in tanks that are:<br />
a. of stainless steel, or lined with epoxy resin or similar coating; and<br />
b. have been used for foodstuffs on the three previous voyages.<br />
Where the oils are to be further processed, using tanks as in (a), only the immediate previous<br />
cargo must be foodstuff or from the permitted list. In due course an evaluation of the<br />
acceptable list will be required by the EC’s technical committee.<br />
The International Maritime Organisation (IMO) has a number of regulations which impact<br />
indirectly on the quality of transport. It is chiefly concerned with preventing pollution of the<br />
environment. Cargoes cause pollution if there is leakage due to an accident, and when tank<br />
washings are discharged.<br />
Vegetable oils are classified by IMO as hazardous, because they harm sea birds and marine<br />
life.They must therefore be carried in vessels with double bottoms and in tanks of stainless<br />
steel or suitable coatings. An exception is made for cargoes from destinations only served<br />
by smaller, older vessels.<br />
Recent experience indicates that contamination by previous chemical cargoes is rare.<br />
Occasional quality problems occur due to the ingress of sea water, resulting in elevated ffa,<br />
and also from overheating, resulting in some oxidation. Overheating may be due to a rapid<br />
heating-up process before discharge or from heat passing from adjacent tanks.
29<br />
CHAPTER 4: BAKERY PRODUCTS<br />
In the first three chapters, we discussed the chemical composition of fat, how its quality is<br />
measured, and how we can ensure that exports reach their destination in good condition.<br />
We will now consider the function of the fat in the food products.<br />
Nutritionally fat is an efficient source of energy, usually measured in calories.A given amount<br />
of fat yields nearly twice the calories produced by the same quantity of the other major<br />
components of foods, the proteins and carbohydrate (starch and sugar).<br />
Fats provide some essential dietary components, that is, those that cannot be synthesised<br />
in the body.These are Vitamins A and E, pro-Vitamin D – which is converted into Vitamin<br />
D in the body – and the fatty acids linoleic (2 double bonds) and linolenic (3 double bonds).<br />
A further function is to contribute to the flavour of the foods, both directly – for example<br />
in the use of butter or olive oil – and indirectly, as a result of chemical changes and interaction<br />
with other ingredients during cooking. Finally of particular interest to the food technologist<br />
is the part that fat plays in developing the structure of various food products.This will<br />
be discussed, first in relation to bakery products.<br />
AIR CONTENT AND THE ROLE OF FAT<br />
We do not generally appreciate that air is an important component of many foods. For<br />
example a loaf of white bread contains about 60% of air by volume. Without the air you<br />
would have a hard flat biscuit, the unleavened bread of the Bible.
30<br />
Before discussing the different types of bakery products we need to understand the nature<br />
of wheat flour, the major ingredient (Table 2).<br />
The protein content of wheat varies from 8-14% or more, depending on variety and growing<br />
conditions. Low protein ‘weak’ flours are used for cakes, and for most pastry and biscuit<br />
types. High protein ‘strong’ flours are needed for bread and puff pastry products.<br />
The most interesting component of the wheat flour protein is gluten. During mixing of<br />
dough it hydrates and, as mixing continues, it becomes elastic and stretches into thin filaments.<br />
When a product is baked the gluten dries, denatures and becomes tough.<br />
In cakes, we do not want a tough chewy texture, and the weak flour may be treated to<br />
reduce the activity of the gluten further.<br />
Cakes<br />
Our first example is a Madeira cake.The fat used in cake manufacture performs two important<br />
functions. Firstly it enables air to be incorporated in the batter, and secondly it contributes<br />
to the tender ‘short’ eating quality of the baked cake. Good aerating properties<br />
require a sufficient liquid oil content to enable air bubbles to be formed, and also the presence<br />
of solids in the form of small crystals (Figure 1).<br />
In a typical two-stage mixing process for a Madeira cake, the fat is first mixed thoroughly<br />
with about half of the flour and beaten to incorporate air. A Hobart-type of mixer fitted<br />
with a whisk type mixing arm is usually used both in the home and in the industry.The mix<br />
is aerated to 40-45% air. Examination under the microscope shows that the air bubbles are<br />
surrounded by fat.
31<br />
Next, the remainder of the flour and the aqueous ingredients are added and mixed.The air<br />
content of the batter has now been diluted to about 15%. Figure 1 is an electron micrograph<br />
of an air bubble in cake batter, magnified about 5,000 times. We are looking at the<br />
internal surface of the bubble, which has been cut in half.The surface consists of liquid oil<br />
and looks smooth: however it shows a number of sharp lines.These are edges of small fat<br />
crystals lying on the exterior surface of the bubble.The diagram in Figure 2 shows the need<br />
for small crystals that line the air cells efficiently. Large crystals would not be effective in<br />
containing and stabilising the air cells (Figure 2).
32<br />
Small crystals are ensured both by correct formulation of the fat blend and by its processing.<br />
A good shortening requires the fat to be in the ‘beta prime’ polymorphic<br />
form, in contrast to the large crystals of the ‘beta’ form.The difference is made clear<br />
under the optical microscope, using polarised light to show up the crystals (Figures 3<br />
and 4).
33<br />
The aspects of polymorphism of fats will be discussed in a later chapter.The word derives<br />
from the Greek for ‘many shapes’.<br />
Coming back to our well aerated cake batter, it is now ready for the oven. When<br />
baking starts and the temperature rises, water vapour is generated and goes into<br />
the existing air cells, as does the carbon dioxide from the baking powder. The air<br />
cells become larger. At this stage they are still surrounded by fat. As the temperature<br />
reaches about 40ºC the fat melts and the air bubbles move into the aqueous<br />
phase. Here the viscosity is increasing due to swelling and gelling of the starch, so<br />
the air bubbles are retained. Eventually the egg protein sets and the cake structure<br />
is fixed.<br />
Measurements under the microscope give air bubbles of an average diameter of 20 microns<br />
(1 micron = 1 millionth of a metre) in the batter; and in the baked cake, of 110 microns.<br />
So, they are still very small.The final air content is 65%. Figure 5 shows a slice of Madeira<br />
cake with its very fine air bubble structure.
34<br />
Three tested formulae for bakery shortenings are given in Table 3.These fats have proved<br />
successful both in cakes and in pastry products.
35<br />
Puff pastry<br />
Its distinctive character is derived from thin layers of a crisp pastry separated by large air<br />
spaces. Dough is made using a ‘strong’ flour of high protein content and a small proportion<br />
of fat, and is formed into a flat rectangle. A layer of special pastry margarine is then placed<br />
on half of the dough area.The other half of the dough is folded over and the parcel is progressively<br />
rolled down in thickness through a pair of pastry rollers.The dough is folded over<br />
once, turned through a right angle and rolled again.<br />
A complete sequence of rolling, folding and turning results finally in many thin layers<br />
of dough inter-leaved with layers of fat. This pastry is baked in a very hot oven. The<br />
steam generated within the dough is retained by the layers of fat and can only escape<br />
after it has lifted the thin layers apart. They then cook to give an attractive crispy<br />
nature.<br />
The properties of the fat must be rather special. It is essentially important that the fat<br />
does not mix into the dough during the rolling process. It must therefore be very<br />
resistant to work-softening. A high degree of plasticity and a somewhat high melting<br />
point is required. <strong>Palm</strong> oil and palm stearin are suitable components for pastry margarine.<br />
Figure 6 shows the effects of correct and incorrect processing of the dough. If there are<br />
too few ‘turns’, not enough layers are formed. If there are too many, the fat has worked<br />
into the dough. Figure 7 shows puff pastry samples prepared in a comparison of two<br />
fats.<br />
Formulae for a puff pastry fat<br />
Successful formulae based on hydrogenated palm oil are in use but have a content of the<br />
undesirable trans fats. It should be possible to use palm stearin instead, for a trans-free<br />
product.<br />
Table 4 shows tested formulae.The third column shows the unusually high melting point of<br />
fat that is required to get good performance in a hot climate. Column 4 gives a softer blend,<br />
which is suitable for the preparation of flaky pastry products.
36<br />
Short pastry and biscuits<br />
The major components of these products are flour, fat and sugar in varying proportions,<br />
together with a small proportion of water. Minor components such as dried fruit or chocolate<br />
chips are added to biscuits to give a particular character.The eating properties – the<br />
texture – of biscuits and pastry vary over a wide range (Figure 8).
37<br />
Think for instance of a ginger biscuit with a crisp tough character and, at the other extreme,<br />
a shortbread biscuit which has a crumbly ‘dissolve in the mouth’ character. In most products<br />
the air spaces play a minor role in the structure.
38<br />
The different textures are obtained by controlling the extent to which the gluten is enabled<br />
to develop. By using a high proportion of fat and ensuring that the flour particles are well<br />
coated with fat, the access of water to gluten can be minimised. A very short, melt-in-themouth<br />
texture is obtained, as in Scotch shortbread. With a lower proportion of fat and<br />
more intense mixing, the gluten is developed to some extent and a somewhat tougher or<br />
crispier texture achieved.<br />
The characteristics of fat are also important. If liquid oil is used, it will fail to coat the flour<br />
particles efficiently because it has a tendency to form droplets. A fat blend must have small<br />
crystals and a smooth easily spreadable texture. <strong>Palm</strong> oil is very effective as a major component<br />
of such a blend.
39<br />
CHAPTER 5: AERATED DAIRY PRODUCTS<br />
Dairy and vegetable oil based creams can be whisked or whipped in such a way that at<br />
least an equal volume of air is incorporated. As a result the products have a more attractive<br />
texture and mouth-feel.<br />
Whipped cream<br />
Whole milk contains about 4% of fat which is present as small globules averaging 7-8<br />
microns in diameter. Each globule is enclosed by a coating or membrane of milk protein.<br />
Cream is traditionally made by skimming the upper layer from milk that has been allowed<br />
to stand. In effect the fatty emulsion phase has been concentrated.<br />
In modern practice this concentration is achieved efficiently in a centrifuge and can be taken<br />
to the stage of single cream (18% fat) or double cream (about 42% fat). If the cream is agitated<br />
sufficiently the fat globules impact on each other and stick together. In due course the<br />
fatty phase becomes more or less continuous and butter is obtained.<br />
If the cream is agitated in such a way that air is incorporated, then it is possible to form a<br />
rigid structure containing about 50% by volume of air. The continuous phase which gives<br />
the product stability is the fat that has coalesced during the agitation. If homogenised cream<br />
is agitated in the same way, a whipped cream of similar air content is obtained. During<br />
homogenisation the individual fat globules are broken down to a size of about 1 micron.<br />
During the aerating process the small globules cluster together and impart sufficient<br />
strength to the air-cell walls to produce a stiff aerated cream. The relatively low melting<br />
point of butterfat means that the aerated cream has limited stability up to about 25ºC in<br />
the European summer and in warmer climates.<br />
Imitation cream<br />
Imitation creams are made by homogenising an emulsion of vegetable fat in skimmed milk<br />
with added sugar. Their behaviour on aeration is then very similar to that described for<br />
homogenised dairy cream. By an appropriate selection of the fat used, aerated structures<br />
of greater stability than real creams can be produced.
40<br />
A very suitable fat for ambient temperatures up to 25ºC is hardened palm kernel oil<br />
(HPKO) with melting point 35ºC and Iodine Value 1.0. For higher ambient temperatures, a<br />
formula of particular interest consists of fully hydrogenated palm kernel oil together with<br />
palm stearin (Iodine Value 19). In this, 66 parts of the HPKO and 34 parts of the palm<br />
stearin are interesterified.This process causes all the fatty acids to change places in a random<br />
manner and alters the melting properties of the mixture.The whipped cream made<br />
using this fat was stable at a temperature of 35ºC. For even higher temperatures an<br />
increase of a few percent of the stearin proportion can be used.<br />
Curves for the solid fat content of HPKO and of the blend are shown in Figure 1.The shaded<br />
area of increased solids in the blend is responsible for its better stability at the higher<br />
ambient temperature, but without affecting the mouth-feel.
41<br />
The structure of the cream is shown in an electron micrograph for a cross-section of an<br />
air bubble (Figure 2).The air cell has a continuous surface layer of fat which is then lined by<br />
numerous intact fat globules. The ‘stand up’ strength of the whipped cream is mainly<br />
dependent on the fat globules.<br />
ICE CREAM<br />
Ice cream is made with dairy cream or an emulsion of vegetable fat with skimmed milk.<br />
Table 1 compares a typical composition of ice cream with that of milk.
42<br />
There is considerable flexibility in the formulation of ice cream.Thus luxury grades containing<br />
15% or more of fat and also reduced fat content products have been marketed. In the<br />
latter type of product, the desired creaminess effect on the palate can be obtained by<br />
changes in the thickeners used.<br />
Ice cream is also a good vehicle for introducing nutritional supplements such as vegetable<br />
sterols which lower blood cholesterol levels, or minerals such as calcium and magnesium<br />
which strengthen bones.<br />
Processing steps in developing ice cream structure<br />
1. Prepare the mix.<br />
2. Pasteurise it to destroy harmful bacteria.<br />
3. Homogenise the hot mix to break up the fat into small globules (0.04-3 microns)<br />
and make the emulsion.<br />
4. Cool the emulsion to 4ºC and store for 2-3 hours or more to allow it to settle<br />
down. Time is needed for the fat to partly crystallise and the milk proteins to coat<br />
the surface of the fat globules.<br />
5. Freeze and aerate the mix<br />
The freezing takes place in a scraped surface heat exchanger. It is the most dynamic stage<br />
in the processing and results in the development of the final structure.The following events<br />
occur in the freezer:<br />
• An increase occurs in the collision frequency of the fat globules due to mechanical<br />
agitation.<br />
• Ice crystals force the fat globules into the decreasing spaces occupied by unfrozen<br />
material, and probably cause shape distortion.The development of ice crystals and<br />
the mechanical action in the freezer cause some breakdown of the emulsion.<br />
• Air is introduced into the mix and dispersed into fine bubbles by the intense agitation.<br />
The partial destabilisation of the emulsion in the freezer is now generally accepted as<br />
important in the formation of a stable ice cream structure.
43<br />
On leaving the freezer about 50% of the water in the mix has turned to ice and the structure<br />
is fully formed.The ice cream is filled into packages, hardened in a cold store at -30ºC<br />
and is then ready for distribution. It is generally held at -17ºC or -18ºC until retailed.<br />
Structure of ice cream<br />
The final structure is similar to that obtained for whipped cream; stability is provided partly<br />
by fat globules lining the air cells but also by the ice in the continuous phase.<br />
Figure 3 shows an electron micrograph of ice cream.The frozen sample has been cut across<br />
and what we see is half of an air bubble. It is lit from above, so that the top part is in shadow,<br />
the lower part being brightly lit.The surface is smooth, consisting of a layer of liquid oil.<br />
The ‘bumps’ in the surface are small fat globules (A) sitting on the outside of the oil layer.<br />
An ice crystal (B) can be seen protruding into the air bubble.The scale is indicated by the<br />
one micron bar. The air bubble is about 5 microns in diameter, while fat globules are 0.5<br />
microns or smaller.
44<br />
The layer of liquid oil forming the surface of the air bubble is derived from fat globules<br />
which were broken open during the intense agitation in the freezer. Figure 4 shows such<br />
broken fat globules.<br />
The dimension of some components of ice cream, as measured under the optical and the<br />
electron microscope, are shown in Table 2.<br />
By the time the product has reached the refrigerator at -18ºC, about 85% of the water is<br />
present as ice and it might be thought that the ice alone would be sufficient to maintain<br />
the structure. However, this is not the case.
45<br />
If an ice cream is made with liquid vegetable oil, a different picture is seen in the electron<br />
microscope (Figure 5).The air bubble is not lined by intact fat globules, and none can be<br />
seen in between the air cells.<br />
The frozen ice cream soon starts to lose air during storage, shrinks in the container and<br />
becomes unattractive. Evidently a good ice cream fat needs to have a solid fat content during<br />
processing.Table 3 gives the proportion of liquid oil remaining of some satisfactory fats<br />
at +5ºC and -5ºC, the temperature before and after freezing.
46<br />
CHAPTER 6: BUTTER ALTERNATIVES<br />
It is no exaggeration to say that the invention and subsequent widespread manufacture<br />
of margarine initiated the development of the oils and fats processing industry as we<br />
know it.<br />
Up to the 19 th century the fats available for food use in North Europe were solely those<br />
produced in the farm yard. Contemporary English cookery books referred only to butter,<br />
beef fat and lard.The industry consisted of the rendering of carcase fats and a limited fractionation<br />
of beef fat to produce stearin for candles. 1<br />
In Mediterranean Europe, olive oil had been the main edible oil in use for some 5,000 years.<br />
Rapeseed was crushed for oil in North Europe, but was only suitable for inedible applications<br />
such as lamp oil. <strong>Palm</strong> oil, imported in small amounts from West Africa since 1780,<br />
was likewise of inedible quality.<br />
The Industrial Revolution in Europe resulted in the movement of the population from<br />
the countryside into the cities, resulting in shortages of food from time to time. In<br />
1865 there was a shortage of butter in Paris and in supplies to the army.This led the<br />
emperor Napoleon III to offer a substantial prize for the invention of a suitable butter<br />
substitute.<br />
French pharmacist and inventor Hyppolyte Mege Mouries took up the challenge. In his<br />
experiments, already in hand in 1867, he noticed that cows starved of food continued to<br />
produce milk. Although reduced in volume, the milk still contained fat. He argued that the<br />
cow was able, by means of enzymes in the udder, to transform its high-melting body fats<br />
into the softer butterfat.<br />
He took carefully rendered beef fat, allowed it to crystallise at about 30ºC and separated<br />
the still liquid portion.This was called ‘oleo-margarine’.The name was taken from oleic acid<br />
from the Greek word for ‘pearl’, referring to the lustrous appearance of the fat when solid.<br />
1<br />
Candles were a valuable commodity in the home, without these, activity in the long winter evenings was very<br />
limited. Coalmine owners supplied candles to underground workers and had to colour them green to prevent theft.
47<br />
The oleo-margarine was melted and mixed with 30-35% skimmed milk, to which 0.1% of<br />
minced cow’s udder was added.The whole was stirred for 2-3 hours at the body temperature<br />
of the cow.The resulting emulsion was churned as if it was real cream.Then chilled<br />
water was added to crystallise the fat. Free water was removed and the fat kneaded until<br />
no more water separated. During the kneading some salt was added. The end product<br />
looked like butter.<br />
The addition of cow’s udder was thought to help the emulsification, but it was soon abandoned.<br />
Mege Mouries won the prize: he patented his process in France, then in the UK in<br />
1869 and in the USA in 1873. He started manufacture in Poissy near Paris, but the enterprise<br />
did not succeed. However the process was licensed to Jurgens in Holland in 1871 and<br />
production also soon started in Germany, Austria, Scandinavia and the USA.<br />
The product proved popular, but soon local supplies of beef fat ran out. Imports from the<br />
USA and Argentina were used. Already in the 1870s some patents described the use of<br />
10-20% of vegetable oils. Initially, carefully prepared unrefined groundnut oil and coconut oil<br />
were used but, as the refining process was developed, other vegetable oils became suitable.<br />
Hydrogenation<br />
The invention of hydrogenation of unsaturated bonds and its development for edible oils<br />
early in the 20 th century widened the ingredients available. Any liquid oil could be hydrogenated,<br />
in other words hardened, to a chosen extent. So, the industry was no longer<br />
dependent on beef fat to provide the structure of margarine.<br />
New ingredients became available, in particular whale oil and fish oils, both of which needed<br />
partial hydrogenation. Although palm oil had been imported for over 100 years from<br />
West Africa it was of very high acidity and suitable only for industrial uses. Some palm oil<br />
of superior quality then became available from Africa that was suitable for the edible fats<br />
industry. A reliable quality of palm oil has been available from Malaysia and Indonesia since<br />
the 1950s.<br />
The dairy industry in many countries reacted strongly to the competition from margarine<br />
and lobbied for restrictive regulation. For example, in Germany, butter and margarine could
48<br />
not be sold on the same premises. Retailers had to erect partition walls and doors to satisfy<br />
the letter of the law.<br />
In Italy a campaign by agricultural organisations led to a ban on the manufacture of margarine<br />
for household use in 1934, followed by a complete ban in 1937. This was relaxed<br />
after the war, but restrictive controls remained until food laws were unified in the European<br />
Union.<br />
A number of countries required the addition of sesame oil as a ‘marker’. A small percentage<br />
was added and could be easily detected in the laboratory, thus preventing margarine<br />
from being mixed with butter. Elsewhere a small amount of starch was added for the same<br />
purpose.<br />
Developments in the USA<br />
The industry in the USA had a particularly hard struggle under both federal and state<br />
restrictions. Margarine manufacture started in 1874; at this time butter was mainly<br />
made on the farm, packed and distributed in small wooden barrels to be portioned<br />
out and wrapped by the retailer. Margarine was handled in the same way, and it was<br />
easy to mix both in the shop. Initial attempts to regulate the trade at state level were<br />
ineffective. Control was achieved under federal law in 1886 requiring proper labelling,<br />
introducing a tax on margarine and the purchase of licences by manufacturers and<br />
dealers.<br />
Later regulations required margarine to be packed and labelled in 1-1b blocks in the factory.<br />
In 1902 a tax of 10 cents/lb was imposed on margarine coloured yellow, making it more<br />
expensive than butter at times.Attempts to colour it with natural palm oil were disallowed.<br />
For a long time margarine could be bought white, with a sachet of colour which the consumer<br />
had to knead into the block. Additional 10-cent taxes were imposed at state level.<br />
Examples of state and federal tax stamps are shown in Figure 1.<br />
During World War II shortages lead to greater use of margarine and a generally favourable<br />
consumer attitude. As a result, federal taxes and licence fees were removed in 1950. Today<br />
the dairy and margarine industries coexist peacefully in the USA and elsewhere.
49<br />
NUTRITIONAL CONSIDERATIONS<br />
Margarine was accepted as a nutritionally satisfactory basic food. Early regulations controlled<br />
the minimum fat and maximum water content and allowed fortification with<br />
Vitamins A and D. In the 1950s concerns over heart disease led to advice to reduce the<br />
intake of cholesterol, present in animal products, and therefore there was a move towards<br />
vegetable oil formulations.<br />
An emphasis developed on the use of ingredients containing the essential linoleic and<br />
linolenic acid which cannot be synthesised in the body.They are the precursors for longer<br />
chain acids of 20 carbons with 5 double bonds and 22 carbons with 6 double bonds. These<br />
are used in the body to make essential hormones and brain components.
50<br />
Linolenic acid is present in rapeseed and soybean oils, which can easily be used in margarines<br />
and spreads.The 20 and 22 carbon acids are present in fish oils.They are very sensitive<br />
to oxidation and need special handling if they are to be used.<br />
Trans fatty acids<br />
Partly hydrogenated oils were generally used, having a significant content of trans fatty acids<br />
(trans fats).Their adverse health effects are now universally accepted.The position is well<br />
stated by Dr A Aro, an experienced researcher who reviewed the results of many studies:<br />
“A high intake [of trans fats] affects the ratio between LDL- and HDL- cholesterol in a way<br />
that is unfavourable compared with all other fatty acids.”<br />
LDL-cholesterol is the ‘bad’ compound associated with an increase in the risk of heart disease,<br />
whereas HDL-cholesterol is the ‘good’ one that removes excess cholesterol.<br />
The body of evidence against trans fats has grown. Further studies have indicated that they<br />
raise the levels of triglycerides and the tendency towards inflammation; both are risk factors<br />
in heart disease.<br />
On the regulatory front, the USA has implemented since January 2006 new labelling regulations<br />
requiring the trans fats content in food products to be declared. The consumer<br />
now understands that trans fats are undesirable, thereby inducing strong moves by manufacturers<br />
to reduce the use of hydrogenated oils.<br />
The New York City government has gone further to tell restaurants and food suppliers to<br />
reduce trans fats to the low level of 0.5g/serving.This has had a knock-on effect, since the<br />
wholesale suppliers to the restaurants have had to reformulate their products, and in practice<br />
would then use the new formulae for all their manufacture. Other local authorities in<br />
the USA may follow suit.<br />
In Denmark, legislation has restricted the trans fats content of all food oils and fats to below<br />
2% since 2003; no adverse effect has been noted on the quality of food products.<br />
In Canada it became mandatory to give the trans fats content on product labels in<br />
December 2005. A government task force recommended that regulations should be made
51<br />
by 2008 but, in June 2007, the government decided instead to request industry to reduce<br />
the trans fats content voluntarily to the lowest possible levels within two years, to avoid legislation<br />
being imposed.<br />
A consequence of these moves against hydrogenated fats is that the use of palm oil products<br />
continues to increase, to provide the required solid fat content.<br />
Reduced-fat spreads<br />
Another nutritional problem led to the development of reduced-fat spreads to meet the<br />
need to reduce calorie intake to combat the rise in obesity. These products cannot be<br />
called ‘margarine’ but need to behave and look like it. A part of the fat content is replaced<br />
by water, and in order to maintain the desired consistency, small amounts of thickening<br />
agent dissolved in water are used.The consumer can then apply a generously thick layer to<br />
a slice of bread, but with fewer calories.<br />
Vegetable sterols<br />
The most recent development with a nutritional objective is the enrichment of<br />
spreads with vegetable sterols. It has been known for many years that the consumption<br />
of vegetable sterols reduces the absorption of dietary cholesterol, and therefore<br />
reduces blood cholesterol level (which is a risk factor for heart disease if it is<br />
elevated).<br />
The vegetable oils consumed normally contain about 0.3gm sterol, but this is not sufficient<br />
to be useful. An additional daily intake of about 2gm reduces blood cholesterol by around<br />
10%. Products containing vegetable sterols are now readily available.<br />
‘Conjugated’ linoleic acid (CLA)<br />
An interesting recent finding is that one particular type of trans fats actually has beneficial<br />
health effect. CLA has one of its double bonds in the ‘cis’ and the second in the ‘trans’ position.<br />
It is naturally present in small proportions in animal fats, which are nowadays consumed<br />
in lesser amounts. CLA inhibits tumour growth and the risk of blocked arteries, and<br />
tends to reduce body fat. Canola oil has been interesterified with CLA and used at the<br />
Malaysian <strong>Palm</strong> <strong>Oil</strong> Board (MPOB) to prepare margarine on a pilot-plant scale. It contains<br />
over 10% CLA.
52<br />
FORMULATION OF FAT BLENDS<br />
How does the food technologist set about formulating products such as margarine or bakery<br />
fat? Two basic properties of the finished product are important – the proportion of solid<br />
fat present at temperatures relevant to its use: and the shape and size of the crystalline solids.<br />
Individual triglycerides may have melting points as high as 60ºC or as low as -10ºC. Any<br />
natural fat is a mixture of a number of triglycerides and will contain a percentage of solid<br />
glycerides at intermediate temperatures. This percentage can be readily measured<br />
because the solid glycerides respond to a magnetic field differently from the liquid. By<br />
measuring at a range of temperatures we can construct a curve of solid fat percentage<br />
against temperature.<br />
<strong>Palm</strong> oil<br />
We need to look at palm oil and palm kernel oil in more detail. <strong>Palm</strong> oil is readily fractioned<br />
into a hard portion (stearin) and a more liquid portion (olein).The process involves holding<br />
the oil at a chosen temperature to allow partial crystallisation to occur, then separating<br />
the olein, usually in a filter press. Depending on process conditions, the properties of the<br />
fractions can be varied.<br />
Curves for the solid fat content (SFC) of palm oil and its products are shown in Figure 2<br />
and compared with butterfat.<br />
The curves for butterfat and palm oil are remarkably close, but there is one important point<br />
of difference. At body temperature (36-37ºC), butterfat is completely molten, but palm oil<br />
has 4-5% solids.This means that it may leave a greasy feel on the palate. Below 15ºC, butterfat<br />
becomes rather hard. As we know, butter taken straight from the refrigerator is not<br />
easy to spread.What is clear from the curves is that palm oil is suitable as a major component<br />
of margarine formulae.<br />
The two curves for palm stearin (2 and 3) show that a variety of properties can be<br />
obtained, enabling the technologist to choose the most suitable. Curve 4 shows a standard<br />
palm olein with appreciable solid content at 15ºC and 20ºC, unlike unsaturated vegetable<br />
oils such as soybean and rapeseed oils.To obtain improved properties, a double fractionation<br />
process is required (Curve 5), but it makes this olein more expensive.
53<br />
The SFC curves for palm kernel oil (PKO) products are shown in Figure 3. PKO has high<br />
solid content at 15ºC and 20ºC and is a firm solid, but above 20ºC it melts rapidly. This<br />
behaviour is even more pronounced in palm kernel stearin, and leads to some special applications<br />
at high value, which are described in Chapter 7.<br />
PKO is a valuable ingredient in margarine blends, in particular when palm oil is also used.<br />
Mixtures of palm oil with PKO have some difficulty in crystallising because the diverse chain<br />
length fatty acids do not fit in together easily. Figure 3 shows this effect in terms of the liquid<br />
oil content. A mixture of 60% palm oil and 40% PKO is still liquid at temperatures<br />
where each of the components on its own would be solid.<br />
When used in a margarine formula, such mixtures improve the melting characteristics in<br />
the mouth, bringing it closer to the behaviour of butter.The mixture is technically described<br />
as ‘eutectic’, derived from the Greek, meaning ‘good melting’.<br />
An economically major ingredient for margarine and spreads is obtained by interesterifying<br />
palm stearin (60%) with palm kernel olein (PKOL, 40%). The stearin component<br />
provides the necessary firmness in the end product, while the PKOL ensures good melt-
54<br />
in-the-mouth properties. The margarine will have a content of short and medium chain<br />
fatty acids similar to those in butter.
55<br />
It is clear that palm oil – which is free of trans fats – offers a direct way of obtaining the<br />
solid content needed to give margarine its consistency. A second way is to prepare fully<br />
hydrogenated oil, such as soybean or rapeseed, and interesterifying it with a proportion of<br />
liquid oil.This is normally more expensive.<br />
WHAT IS THE RIGHT CONSISTENCY?<br />
The desired consistency of margarines and spreads can be defined as being spreadable at<br />
the temperature of use. Margarines have a physical behaviour in between that of liquids –<br />
which flow when poured – and solids, which move as a whole when pushed.<br />
They have an internal structure that consists of a network of very small crystals of the solid<br />
triglycerides. This three-dimensional network holds the liquid oil component and also the<br />
emulsified aqueous phase.The network is rigid enough so that the product looks solid but<br />
is easily disturbed when ‘pushed’.Then the liquid component takes over, and the margarine<br />
flows until the pushing stops.<br />
‘Spreadability’ means we can cut a portion of margarine from a block or out of a tub, apply<br />
it to a slice of bread and spread it. Physicists define the force needed to make the margarine<br />
flow as ‘yield value’.This can be measured with simple equipment and used to compare<br />
the spreadability of different products. The spreadability changes quite rapidly with<br />
temperature. It may be said that the spreadability of butter is not ideal. It is good between<br />
15ºC and 25ºC, but outside this range is either too hard or too soft in a warm climate.The<br />
margarine manufacturer can improve this.<br />
Experience shows that a SFC between about 15% and 35% is suitable. See Figure 5 for SFC<br />
curves of various products.<br />
A second factor is that the solid fat must be in small crystals. As we have seen in relation<br />
to shortenings, this requires the beta prime polymorphic form (Figure 3, Chapter 4).<br />
Problems arose in Canada when margarine was formulated with hydrogenated rapeseed<br />
oil, the local produce. It transformed during storage to the beta form, giving an unsatisfactory<br />
appearance and a gritty feel on the palate (Figure 6).
57<br />
The reason for the transformation is that the canola oil contains almost solely fatty acids of<br />
18 carbon atoms. When the margarine was reformulated using a proportion of palm oil<br />
(with palmitic acid of 16 carbon atoms) the change to the beta form was made difficult due<br />
to the diversity of chain lengths, and the product was stable in the prime form.<br />
HISTORIC MARGARINE FORMULAE<br />
Table 1 gives a number of published formulae. Apart from the first, the formulae all contain<br />
trans fats from the hydrogenated component.<br />
Experimental formulae that have satisfactory characteristics and are free of trans fats have<br />
been developed in the laboratories of MPOB (Table 2).
58<br />
While manufacturers do not generally reveal the blend formulae in use, analyses show that<br />
today, margarines in Europe are substantially free of trans fats and that there have been big<br />
reductions also in the USA. At the same time, their imports of palm oil and stearin have<br />
increased.<br />
Improved margarine processing<br />
Mege Mouries’ original process was soon improved.The margarine emulsion was pumped<br />
in a thin layer onto a rotating drum, which was chilled internally with ice water or a refrigerant.<br />
Crystallisation in the desired small crystals was initiated.The partly crystallised mass<br />
was scraped off into an open trough fitted into a rotating shaft fitted with beater arms.The<br />
fully crystallised fat was rested for a time and packed.<br />
This processing is today essentially unaltered, but now it is carried out within a scraped surface<br />
heat exchanger (Figure 7) and then a second cylinder – the ‘worker unit’ – where fat<br />
is intensely mixed (Figures 8 and 9). After a period in a resting tube, the product is ready<br />
for packing; today, usually into 250gm or 500gm packs or plastic containers.<br />
Table 3 gives prices of products on the shelves of a London supermarket.The second column<br />
gives the price calculated for the fat component (i.e. the nutritional element).
60<br />
Production and consumption<br />
Margarine production has shown continuous growth, with some increase in rate during and<br />
after World War I. During World War II, the high quality of the product was recognised and<br />
when rationing was relaxed, production went up. The slower increase from about 1960<br />
was due to the lower fat content of the increasing market for reduced fat spreads. Figure<br />
10 shows world production data for margarines and spreads.<br />
It may be noted that Denmark has the highest per capita consumption of margarines and<br />
spreads. This is because its important dairy industry exports much of the production.<br />
Consumption in some Western countries is listed in Table 4.<br />
VANASPATI<br />
In the Indian subcontinent, butter very quickly develops an off-flavour mainly due to<br />
hydrolytic breakdown of the glycerides at the high ambient temperature. It has therefore<br />
been traditional to market ‘butterfat ghee’. This is made by melting butter and boiling off<br />
the water layer. A desirable flavour develops.
61<br />
In 1930 Hindustan Lever developed vanaspati as a vegetable oil-based alternative.<br />
In order to find acceptance among consumers, some butter flavour was added and<br />
the appearance of butterfat ghee was imitated. When the melted butterfat cools<br />
slowly, it crystallises in rather coarse grains, up to 1-2mm across, with a little free oil<br />
remaining.
62<br />
Figure 11 is a photograph of the crystals in a thin layer of vanaspati. This appearance is<br />
regarded as important by the consumer and therefore had to be achieved in the alternative<br />
product.<br />
Government regulations initially required the melting point to be no higher than 37-38ºC but<br />
subsequently the range was widened to 41ºC. A suitable product was obtained by partial<br />
hydrogenation directed towards the production of trans fats in preference to saturated acids.<br />
Similar products are used in the Middle East and Egypt, and by expatriate Indian populations<br />
in other countries. Most of these countries rely on imported oils for a large part of<br />
their consumption. The market for vanaspati in Pakistan is 1.7 million tonnes, while the<br />
world market was estimated at 5-6 million tonnes in 2009.
63<br />
Formulation<br />
<strong>Palm</strong> oil has the desired melting point for vanaspati. However, when crystallised slowly, it<br />
forms small crystals and a high proportion of liquid oil. A better appearance can be<br />
obtained with a blend containing some hydrogenated oil, or by interesterification. Some satisfactory<br />
experimental formulae with zero trans fats are shown in Table 5.<br />
In the 1980s, when vanaspati was largely based on hydrogenated vegetable oils, the trans<br />
fats content was high with a figure of 53% for India, more than 50% for Iran and 27% for<br />
Pakistan. However, as palm oil became available, a lower trans fats value of 3.7% was reported<br />
in Pakistan.<br />
More recently, as consciousness of the adverse effects of trans fats spread, Iran introduced<br />
a limit of 20%, to be reduced further with time. In India, adverse comments appeared in<br />
the press in April 2009 about analyses of products in the market with 23-24% trans fats.<br />
At present the formulations used in Pakistan are varied. Due to the high summer temperatures<br />
a firmer product is required (Table 6).
64<br />
The processing of vanaspati is very simple.The warm blends are filled into large tins, typically<br />
28lb, and placed in a temperature controlled store at 21-22ºC until cold.
65<br />
CHAPTER 7: THE LAURIC OILS<br />
The oil palm is the only crop yielding two different types of oil.The yield of palm kernel oil<br />
(PKO) is about 10% of the oil derived from the flesh.The most interesting feature of the<br />
two oils is the substantially different make-up of the fatty acids.<br />
<strong>Palm</strong> oil, like most vegetable oils, contains mainly fatty acids with 16 or 18 carbon atoms.<br />
PKO typically contains 48% lauric acid with only 12 carbon atoms and another 9-10% of<br />
fatty acids with shorter chain length.The only similar oil available commercially is coconut<br />
oil.These two are often described as lauric oils.<br />
Figure 1 shows how the production and export of the two oils have developed over 20<br />
years. There is a striking difference. The availability of PKO has grown in line with the<br />
increase in palm oil supplies. The volume of coconut oil has, however, remained about<br />
static.
66<br />
The oil palm and coconut palm are members of a large family of some 3,000 species.<br />
Several hundred of them are native to the Amazon basin in South America, and some have<br />
been exploited by the native populations for their oil content.<br />
Chemical analyses of kernel oils from a number of these species show that they are all lauric<br />
oils, and this is probably true of all the palm family. Attempts to commercialise some of<br />
these kernel oils have failed. The exception is babassu oil – a few thousand tonnes have<br />
occasionally appeared in the market.<br />
The babassu is a large palm of the Amazon forest and it grows in dense natural stands.The<br />
kernel forms only 10% of the fruit, so it must be extracted on site from the nut for<br />
economies of transport. However, it is encased in a thick and extremely hard shell, which<br />
presents a technical challenge. It has been estimated that 1-2 million tonnes of oil per year<br />
are not being utilised. A commercial evaluation of the oil has indicated that its properties<br />
are intermediate between PKO and coconut oil and that it would serve similar applications.<br />
Table 1 shows the fatty acid composition of the lauric oils – note the contrast with palm oil.<br />
Oleochemical demand<br />
The content of medium and short chain length fatty acids renders the lauric oils of great<br />
interest to the oleochemical industry.Worldwide, it uses up to half of the lauric oil supplies.
67<br />
The demand from both the food and oleochemical industries means that lauric oils usually<br />
fetch a premium over other vegetable oils.The rapid development of the oleochemical<br />
industry in Malaysia is indirectly illustrated by figures for domestic disappearance of 53,000<br />
tonnes in 1986, rising to 1.41million tonnes in 2009, most of which was converted into<br />
chemical products for export.<br />
Probably the biggest chemical use of lauric oils is in soap making, as has been practised<br />
since the time of the ancient Egyptians. A good soap formula consists of 75-<br />
80% tallow, palm oil or palm stearin and 20-25% lauric oil. <strong>Function</strong>ally, the shorter<br />
chain fatty acids impart good foaming while the long chain fatty acids give the foam<br />
persistence.The foam suspends particles of dirt and is important for a good cleansing<br />
action.<br />
Other technical uses require, as a first step, the formation of fatty acid compounds such as<br />
esters, fatty alcohols, a variety of nitrogen compounds and metal soaps. Further chemical<br />
modification is often required to reach end products with a long list of applications in a variety<br />
of industries.The list includes personal care products, surface active agents, anionic and<br />
nonionic detergents, fabric softeners, lubricants, mineral processing aids and corrosion<br />
inhibitors.<br />
FOOD USES OF PKO<br />
The solid fat content curves for PKO products are shown in Figure 3, Chapter 6. The steep<br />
melting curve of PKO in comparison with palm oil should be noted. This is even more<br />
marked in palm kernel stearin (PKSt).<br />
When eaten, foods with a high content of PKO give rise to a pleasant cooling sensation<br />
on the tongue due to heat being rapidly abstracted as the oil melts.This may<br />
be noted in biscuits with a cream filling, in whipped cream and some confectionary<br />
products.<br />
Margarines and spreads<br />
Another feature of PKO behaviour of particular value in margarine formulations is its formation<br />
of eutectic mixtures with palm oil, as shown in Figure 4, Chapter 6.
68<br />
Dairy products<br />
PKO is the preferred replacement for butterfat in various dairy products because:<br />
1. Countries like Malaysia, which have an inadequate supply of fresh milk, import<br />
skimmed milk powder and make recombined ‘filled’ milk with locally available<br />
vegetable oil.The product may be marketed in cans or as UHT processed in<br />
tetrapak cartons.<br />
2. There is less risk of deterioration during transport of skimmed milk powder than<br />
of full cream milk powder.<br />
3. Filled milk is cheaper.<br />
4. In some products, better performance can be achieved with a ‘tailor-made’ fat blend.<br />
There are long-standing recommendations from the International Dairy Federation for the<br />
specifications of the oils to be used.These include clean flavour, low acidity and oxidation,<br />
and low levels of trace metals and impurities. Refined PKO has no difficulty in meeting these<br />
specifications.<br />
Some ‘filled’ milk products are used as a powder – for example, coffee ‘whitener’ and coffee<br />
‘creamer’ used in drinks dispensers and provided in sachets in restaurants or fast-food<br />
outlets.These products are required to have a long shelf life; therefore, fully hydrogenated<br />
PKO (with zero trans fats) is preferred. PKO is a very suitable component for ice cream<br />
and is widely used.<br />
There is a limited market for cheese made with vegetable oil.A large part of cheese flavour<br />
is derived from the short chain fatty acids in butterfat. A satisfactory mozzarella cheese can<br />
be made using a blend of 70% palm kernel olein (PKOL) with 30% PO. This blend has a<br />
similar solid fat content to butter but is cheaper.The fatty acids of PKOL help to develop<br />
the desirable flavour. Mozzarella cheese is an important ingredient in pizzas. Danish-type<br />
cheeses have been made using a blend of 50% palm oil, 40% coconut or PKO and 10%<br />
rapeseed oil.
69<br />
Frying<br />
PKO and PKOL are suitable for frying. A particular use is for frying nuts intended for snack<br />
foods or in bakery products. PKOL blended with palm olein is useful for shallow pan frying,<br />
but not deep fat frying, because the mixture tends to foam.The high stability of PKO<br />
also makes it suitable for the ‘popping’ of popcorn.<br />
Biscuits<br />
A blend containing 40% PKOL with palm olein forms a eutectic mixture similar to that<br />
described for PKO with palm oil. It finds applications as spray oil for certain types of biscuit<br />
such as cream crackers. The purpose is to provide an attractive shiny appearance and to<br />
act as a moisture barrier so that the crackers remain crisp.The high stability to oxidation<br />
of the blend is important.<br />
PKO is used in other types of biscuits such as Bourbon Creams, where two biscuits are sandwiched<br />
with a layer of PKO-sugar mixture. In the manufacturing process, the warm fluid filling<br />
is deposited mechanically on one biscuit and the second biscuit is placed on top. As<br />
PKO crystallises very rapidly, the timing of the process must be judged so that there is still<br />
enough liquid to ‘glue’ on the second biscuit.<br />
Dietary product<br />
A special use of PKO is in the manufacture of medium chain triglycerides (MCT).This<br />
is a dietary product used for people with a metabolic problem, who are unable to<br />
digest ordinary fats. MCTs are made by first fractionating the fatty acid components<br />
of PKO and then re-synthesising those of the shorter chain lengths into triglycerides.<br />
A blend of 80-90% of capric (10 carbons) and 10-20 % of caprylic (8 carbons) is preferred.<br />
A major area of use for PKO – and one where considerable added value can be obtained<br />
– is in fats for confectionery use.This is discussed in Chapter 8.
70<br />
CHAPTER 8: CONFECTIONERY FATS<br />
<strong>Palm</strong> oil and palm kernel oil (PKO) are, in different ways, valuable ingredients in confectionery<br />
products. The best starting point to understand the special character required in<br />
confectionery fats is cocoa butter, the fat of the cocoa bean.<br />
When the Spaniards arrived in America in the 16th century they found the Aztecs were<br />
making a popular drink called 'chocolatl' from powdered roasted cocoa beans. Recipes also<br />
contained maize and flavouring like chilli or vanilla.<br />
Research has shown that this drink was in use more than 3,500 years ago. Ancient pottery<br />
vessels found in southern Mexico, where the cocoa tree is native, contained brown<br />
residues. When analysed, the residues were found to contain theobromine, an important<br />
substance specific to the cocoa bean.<br />
The Spaniards introduced the bean and its use as a drink to Europe. It became a luxury<br />
item favoured by the aristocracy. Chocolate bars, as we know them, were developed in the<br />
18 th century, with Fry of Bristol being a pioneer.<br />
The chocolate bar requires extra fat over and above the natural fat content of the bean.<br />
The added fat is obtained by pressing roasted cocoa beans, leaving a cocoa powder with a<br />
much reduced fat content.<br />
CHARACTERISTICS OF CHOCOLATE<br />
Chocolate has a number of attributes valued by the consumer. It has an attractive, smooth<br />
but shiny appearance.The chocolate bar has a firm solid texture and breaks cleanly when<br />
a bite is taken. It melts rapidly in the mouth, releasing its complex flavour.<br />
The flavour is developed in two stages.After harvest the beans are allowed to ferment naturally<br />
for 2-3 days before being dried. Later they are roasted and ground, resulting in the<br />
cocoa mass used in chocolate.<br />
The appearance, texture and melting behaviour depend on the properties of the fat,<br />
whereas the flavour is derived mainly from the cocoa solids.
The formulae for chocolate vary quite widely between manufacturers, but Table 1 shows a typical<br />
example of plain chocolate and the composition of the roasted ground bean (cocoa mass).<br />
71<br />
Cocoa butter is much more expensive than other vegetable fats - at the time of writing, it<br />
is 2 1 / 2 times the price of palm oil.Therefore, there is interest in the use of alternative fats<br />
which must not, however, alter the physical appearance and melting behaviour of the<br />
chocolate.<br />
There are two possibilities: firstly to replace some or all of the added cocoa butter in<br />
chocolate; and secondly to make a more economical product using an alternative fat with<br />
cocoa powder. Each approach has limitations.<br />
The concept of chocolate is protected legally in many countries. In the European Union (EU)<br />
the amount of vegetable fat that may be added is restricted to 5% of the end product.<br />
The properties of PKO products are quite similar to those of cocoa butter, as is evident<br />
from the solid fat content (SFC) curves shown in Figure 1.<br />
Unfortunately the lauric oils are not compatible with cocoa butter.They form eutectics, similar<br />
to that formed with palm oil.The chocolate is softened and loses its desirable crispness.<br />
Cocoa butter<br />
The composition of cocoa butter is very simple (Table 2).The fatty acids are also the major<br />
components of palm oil, albeit in different proportions. However, early attempts to make<br />
confectionery fat from palm oil were unsuccessful.
72<br />
In 1956, researchers at Unilever obtained a patent for a cocoa butter equivalent (CBE) fat;<br />
in other words, a fat that can be mixed with cocoa butter in any proportion without changing<br />
its hardness or melting behaviour.<br />
This achievement required first a detailed knowledge of the triglycerides present in cocoa<br />
butter. Typically three major components 1 made up 85% of the fat: POP (18%); POSt<br />
(39%); and StOSt (28%).<br />
These glycerides are symmetrical, with the unsaturated oleic acid placed on the glycerol<br />
molecule in the middle position between the two saturated fatty acids.This proved to be<br />
an essential feature of a compatible fat.<br />
1<br />
P = palmitic acid, St = stearic acid, O = oleic acid
73<br />
The fatty acids are of similar chain length and identical structure, resulting in the characteristic<br />
sharp melting behaviour of cocoa butter. <strong>Palm</strong> oil contains two of these glycerides in<br />
useful concentration, i.e. POP 29% and POSt 5%. They can be concentrated by a partial<br />
crystallisation and filtration to separate the higher melting portion and a second crystallisation<br />
at a lower temperature to remove the more unsaturated portion.<br />
The resulting palm mid-fraction (PMF) forms about 20% of the original palm oil and contains<br />
typically 57% POP, 11% POSt and 2% StOSt. PMF is miscible with cocoa butter but<br />
has a lower melting point and, to match its characteristics, it needs to be blended with<br />
another fat rich in StOSt.<br />
A number of seeds from tropical trees have a suitable fat; in some cases the desired component<br />
has to be concentrated by fractionation.Their content of the important glycerides<br />
is shown in Table 3, together with cocoa butter.<br />
Seed fats<br />
It is not possible to prepare blends which exactly match the main glycerides of cocoa butter,<br />
but blends are available that are completely compatible with cocoa butter (Table 4).<br />
In terms of availability, all the seed fats listed in Table 3 (except PMF) present some difficulty.<br />
Illipe nuts are obtained from tall forest trees growing in remote parts of Borneo.The trees do<br />
not flower every year and the harvest of nuts can vary from nil to 50,000 tonnes. Attempts
74<br />
to grow them in plantations have not succeeded. Furthermore, they grow in rainforests and<br />
the harvest is gathered from the ground, so a varying degree of biodegradation occurs.<br />
Shea nuts are also gathered from the ground in the rainforests of West Africa.The oil content<br />
is 44-55%, but includes some undesirable components and the oil is difficult to refine.<br />
Sal nuts are collected from forest trees in India. Supplies of kokum fat are small, but its high<br />
content of StOSt is valuable. Most mangoes are consumed as fresh fruit, so kernel collection<br />
is only feasible from those that are industrially processed.<br />
Cocoa butter from different sources shows some variability - the Brazilian product is softest,<br />
while Malaysian cocoa butter is the hardest. At least some of this variability is due to<br />
climatic conditions. This was proved by a very elegant experiment, in which heating was<br />
provided to raise the temperature of half of a tree by a few degrees during the period of<br />
fruit formation.The warmer part of the tree produced significantly harder fat.<br />
Hardness at room temperature is a highly desirable characteristic, provided the melting at<br />
mouth temperature is still rapid. It is possible to improve the behaviour of Brazilian cocoa<br />
butter by using a CBE rich in the StOSt glyceride, such as kokum fat.The EU legal definition<br />
of chocolate permits the addition of vegetable fat from the list shown in Table 3 at a<br />
level of 5% of the finished product, equivalent to about 15% of the fat content. Legislation<br />
varies elsewhere.<br />
Improving chocolate behaviour<br />
Since the price of CBE fats is often half or less than that of cocoa butter, such additions<br />
represent a worthwhile saving and can help improve the behaviour of the chocolate.
The formula of dark chocolate (Table 1) can be modified by using 7 parts of cocoa butter<br />
and 5 parts of CBE as the added fat.<br />
75<br />
Products containing more than 5% CBE may no longer be called chocolate. They are<br />
described as super coatings. All the added cocoa butter can be replaced by CBE or, to go<br />
further, a low-fat cocoa powder (containing 11% cocoa butter) can be used in place of<br />
cocoa mass together with a higher level of CBE.<br />
A large part of today's market for chocolate is for milk chocolate, in which usually there is<br />
less cocoa and a large part of the overall flavour is given by the milk solids and fat. Butterfat<br />
contents of 5-20% or even higher are used in different quality products.The butterfat softens<br />
the texture of the chocolate. By selecting a CBE fat such as Blend 4 or 5 in Table 4, a<br />
firmer product is obtained.<br />
CRYSTALLISING OF CHOCOLATE<br />
Molten chocolate is a suspension of the solid ingredients in liquefied fat.To obtain the shiny solid<br />
surface, a special method of crystallising the fat is used.The chocolate is cooled slowly, with constant<br />
stirring until it thickens. It is then carefully warmed a few degrees and allowed to set.<br />
The science behind this process is fascinating. Although the glyceride composition of cocoa<br />
butter is very simple, its crystallising behaviour is very complex. It can go into six different<br />
arrangements of the glycerides in the crystals, with increasing melting points (Table 5).<br />
The desired form giving a shiny surface is Form V. During the crystallising process, a mixture<br />
of the forms develops. By reheating the mass to just below the melting point of Form V, the<br />
less stable forms melt. Subsequently the remaining crystals act as nuclei to induce recrystallisation<br />
in Form V.<br />
Transition to Form VI, which is the most stable form, can be induced by temperature fluctuations<br />
during storage. Formation of Form VI, which is characterised by larger crystals, leads<br />
to some fat crystals appearing on the surface of the chocolate, giving it a grey appearance<br />
called 'chocolate bloom'.While this is harmless, it is unattractive and consumers may think<br />
it indicates mould. As the Form VI develops further the chocolate loses its smooth texture<br />
and becomes gritty on the palate.
76<br />
Figure 2 shows electron micrographs of all six forms. At the thousand-fold magnification<br />
used, the difference between Forms V and VI is dramatic.The last section shows the crystals<br />
of bloom on a bar of chocolate, clearly of Form VI.
77<br />
CONFECTIONERY FATS FROM PKO<br />
PKO has the rapid melting characteristics required in a confectionery fat, but its melting<br />
point (28°C) is too low for a direct replacement of cocoa butter in chocolate.<br />
Figure 1 shows the SFC curves of cocoa butter and various PKO products.The stearin prepared<br />
from PKO has a solid content profile very close to cocoa butter. Hydrogenated<br />
stearin (having virtually zero trans fats) is also suitable for chocolates, especially in hot climates.<br />
Because PKO products cause an unacceptable softening of the chocolate, they can be used<br />
only if the cocoa butter content is 5% or less of the product. This means using a low-fat<br />
cocoa powder. A typical formula using palm kernel stearin (PKSt) as a cocoa butter replacer<br />
(CBR) is shown in Table 6.<br />
The total fat content is 32.5%, of which 1.5% is cocoa butter contributed by the cocoa<br />
powder. Figure 3 shows chocolate made with hydrogenated PKSt.<br />
PKO products can develop off flavours if a fat splitting enzyme (lipase) - derived from contamination<br />
by yeast or mould - is present.The lipase splits off some fatty acids and the short<br />
chain acids characteristic of PKO have a strong soapy flavour.<br />
Contamination can be introduced by an ingredient such as milk powder or as a result of<br />
poor hygiene. Precautions need to be taken by testing ingredients and ensuring good<br />
hygiene.This drawback does not arise when a non-lauric confectionery fat is used.<br />
Other CBRs<br />
Fats with a suitable sharp melting behaviour can be made by partial hydrogenation of oil
78<br />
high in oleic acid. <strong>Palm</strong> olein is a good starting material, although other fats are also used.<br />
It is necessary to use a catalyst and hydrogenation conditions that maximise the formation<br />
of trans-oleic (elaidic) acid.<br />
A typical product has about 18% trans fats and only a small increase in the saturated stearic acid.<br />
However, it does not fit in well with current recommendations to minimise trans fats in foods.<br />
Coatings for ice cream<br />
Ice cream bars and lollies (stick confectionery) coated in chocolate are very popular.They<br />
are handled at a low temperature (below -10°C) from manufacture to retail sale. A true<br />
chocolate is very brittle under these conditions and often flakes off.<br />
Suitable fat blends are specially formulated according to the method of use. For bars a palm<br />
oil-PKO blend can be used, the lower melting eutectic being an advantage here.<br />
For stick confections a PKO or coconut oil blend with liquid oil may be used.The manufacturing<br />
process involves dipping the ice cream into the coating, withdrawing it and, in some<br />
cases, applying a layer of crushed nuts or crisp biscuit crumbs.The coating must be 'tacky'<br />
to permit adhesion of the layer, and must set immediately before being packed. The oil<br />
blend is subtly adjusted to the timing of the process.
79<br />
CHAPTER 9: FRYING OILS<br />
<strong>Palm</strong> oil and palm olein are widely used for frying because they are economic and effective.<br />
However, it is of primary importance for every business to understand the competition<br />
it faces.This chapter describes the development of alternative oils in the context of the<br />
technical requirements for satisfactory frying oil.<br />
Most cooking processes are carried out at the boiling point of water (100°C).This is true<br />
even in oven baking. Although the oven temperature is well above 100°C, the high moisture<br />
content of food, such as meat joints and cake batter, means that the food itself does<br />
not get above 100°C except for the surface layer, which develops a brown crust and an<br />
attractive flavour.<br />
Similarly during frying, which is carried out with the oil heated to a temperature of 170-<br />
180°C, the food itself gets no hotter than about 100°C except on its surface. Frying in the<br />
kitchen may be done in a shallow pan or in a deep pan. In the case of the shallow pan, a<br />
little oil is used.The food is cooked on one side, turned over and cooked on the other side.<br />
Virtually all the oil is absorbed by the food.<br />
Some kinds of food, for example potato chips or French fries, are best cooked fully<br />
immersed in a deep pan full of oil. A small proportion is absorbed and the rest is kept<br />
for re-use. Deep pans are used in fast-food restaurants everywhere, while snack foods<br />
such as potato crisps and instant noodles are manufactured in large continuous frying<br />
baths.<br />
Inevitably, over time, some chemical changes take place in the oil. Initially these contribute<br />
to the desirable taste of the cooked food. However, over time, some oxidation<br />
of the oil takes place, occurring mainly at the unsaturated double bonds of the fatty<br />
acid chains. The resulting changes produce an unpleasant taste as the oil has become<br />
rancid. Eventually some polymerisation occurs, the viscosity becomes higher and more<br />
oil is absorbed into the food.When the quality of the food is affected, the used oil has<br />
to be discarded and replaced. Clearly this has an important effect on the economics<br />
of use.
80<br />
Two main factors control the useful life of frying oil:<br />
• The first is good practice in its use.The temperature must be controlled, the<br />
equipment kept clean and the correct oil level maintained. During frying, oil is<br />
absorbed by the food product and therefore removed from the pan. It is replaced<br />
by fresh oil, so maintaining quality. Clearly a high rate of oil turnover is desirable.<br />
• The second is the choice of frying oil.The susceptibility of an unsaturated fatty<br />
acid to oxidation increases with the number of double bonds in the chain. Linoleic<br />
acid (2 double bonds) oxidises 10 times more rapidly than oleic acid (1 double<br />
bond), while linolenic acid (3 double bonds) oxidises at least 20 times more rapidly<br />
than oleic.<br />
Therefore oils with more than 3% linolenic acid are not regarded as suitable for<br />
deep-fat frying.Vegetable oils all contain some minor components, the antioxidants,<br />
which inhibit the action of oxygen on the unsaturated bonds.<br />
The fatty acid composition of palm olein is shown in Table 1 on page 81. It has a very low<br />
level of the sensitive linolenic acid and a moderate level of linoleic acid. The other main<br />
components - palmitic and oleic acids - are highly stable to oxidation. In addition palm oil<br />
and olein are relatively rich in protective antioxidants especially the Vitamin E tocotrienols.<br />
These good properties have been recognised. It is estimated that globally some 10 million<br />
tonnes of palm oil and palm olein are used annually in restaurants, fast-food outlets and<br />
industrial deep-fat fryers.There is also substantial domestic use.<br />
Nutritional guidelines<br />
The high content of the saturated palmitic acid undoubtedly contributes to the stability of<br />
palm oil in frying, but is often questioned with regard to its nutritional benefits, especially in<br />
terms of blood cholesterol modulation.<br />
With increasing understanding of the association between diet and health, many countries<br />
have published nutritional guidelines for their populations.There is broad agreement among<br />
developed countries that fat intake should be no more than 30% of total energy (current<br />
fat consumption in the West is about 35-37% of energy).
81<br />
Within that 30% it is recommended generally that saturated fatty acids (SFA) should be no<br />
more than 10% of total energy intake, with polyunsaturated (PUFA) at 7-10% and monounsaturated<br />
(MUFA) at 10% or more.<br />
The recommended level of SFA refers to the total amount of fat consumed. Competitive<br />
marketing considerations have led to a desire for the lowest possible SFA content in oils<br />
used for frying. Some commodity oils fit this specification quite well, for example soybean<br />
oil (SFA 15%) and rapeseed oil (SFA 7%).<br />
However they also have high levels of PUFA, and especially of linolenic acid (>7%) and<br />
therefore lack stability at the frying temperature. As a result, plant breeding programmes<br />
for these oils and others have been undertaken to develop frying oil with a fatty acid composition<br />
that could confer higher stability.
82<br />
Ideal specifications<br />
It would be instructive to first draft a specification for frying oil that meets as far as possible<br />
the current nutritional and technical optima.<br />
The following requirements need to be met:<br />
• Linolenic acid less than 3%, as low as possible<br />
• Linoleic acid - a good fried flavour needs about 10% while higher levels can lead to<br />
off flavours due to oxidation<br />
• Saturated acids below 15%<br />
• Oleic acid 65-70%, can be higher<br />
More precisely:<br />
• Saturated acids 10-15%<br />
• Oleic acid 65-75%<br />
• Linoleic acid 15-20% (I would suggest 10-15% at most)<br />
• Linolenic acid 1-2%<br />
<strong>Palm</strong> oil and palm olein, in their current form, are excellent frying fats. However, given the<br />
desire for higher oleic varieties and efforts to reduce saturates content, palm olein of<br />
higher unsaturation - obtained through multiple fractionation - is becoming increasingly<br />
available.<br />
Through process innovations, it is possible to obtain palm olein with unsaturated fatty<br />
acid content (mostly oleic) in excess of 62% of its composition. Advanced research,<br />
especially through hybrid selection or genetic modification, has demonstrated the<br />
potential to develop palm olein with a fatty acid composition that mirrors olive oil. Such<br />
a composition would be competitive against the new varieties of frying oils described<br />
next.<br />
MODIFIED OILS<br />
Several modified oils have been produced using conventional plant breeding techniques<br />
and tested in frying trials. We will now review results of these breeding programmes and<br />
of any practical frying results reported in using the modified oils.
83<br />
Modern analytical techniques enable a single seed to be sampled and its fatty acid composition<br />
to be determined while the seed remains viable. If therefore, the analysis reveals an interesting<br />
variation from the standard composition, the seed can be used for further breeding.<br />
Furthermore, when the crop is an annual one, it is possible by the use of greenhouses and<br />
artificial lighting to produce three generations per year. Rapid progress can be made<br />
towards a new product. In contrast, the oil palm requires 3-5 years before the oil from a<br />
new plant becomes available for testing and, furthermore, the replanting of a large area<br />
would require some years compared to an annual crop.<br />
Sunflower oil<br />
A thorough collaborative project was carried out from 1994-1996 between different<br />
research centres in the European Union to test the frying properties of High Oleic<br />
Sunflower <strong>Oil</strong> (HOSFO). <strong>Palm</strong> olein was used in the trials as the reference oil.The composition<br />
of the oils used is shown in the first three columns of Table 1.The last column shows<br />
the composition of Nusun, an equivalent product in the USA.<br />
The oils were used to prepare, on an industrial scale, potato crisps and pre-fried frozen<br />
French fries.The products were submitted to extensive analytical tests and to tasting tests<br />
before and after storage.<br />
The conclusion was that the HOSO was as good as palm olein for both the French fries<br />
and potato crisps.The storage life of the potato crisps was shorter than when palm olein<br />
was used, but adequate for retail purposes.
84<br />
Today HOSO is increasingly used for snack food frying in Europe, either replacing palm olein<br />
or used in a blend with it. Consumption figures for the high oleic oils are not available in Europe<br />
but in the USA, 200,000 tonnes/year of the equivalent Nusun is currently in use. However, a<br />
significant premium accompanies HOSO, curtailing its use for many low-cost foods.<br />
Rapeseed oil<br />
A high oleic rapeseed oil has been developed by the Dow chemical company, under the<br />
name Natreon. Its composition in comparison with typical commercial oil is shown in Table 2.<br />
The most important feature of the Natreon composition is the reduction in the highly-sensitive<br />
linolenic acid.The oil was compared in domestic scale deep-fat frying of potatoes with<br />
HOSO and palm olein.<br />
The conclusion, after a number of analytical tests and tasting of both the used oils and the<br />
French fries, was that the three oils were comparable. The potatoes still had acceptable<br />
taste after the oil had been used for 66 hours. No production figures are available for high<br />
oleic rapeseed oil, but it is in commercial use.<br />
Soybean oil<br />
Experimental quantities of soybean oil with various modified compositions have been produced<br />
(Table 3). Small-scale frying trials were conducted with bread cubes, potato crisps,<br />
French fries or tortilla chips.The modified oils all performed better than the standard oil.<br />
Significantly better flavour and storage performance were reported for the oils with the<br />
lowest linolenic acid content. In one trial, oil with 0.8% performed better than one with<br />
2.0%.This result provides good evidence for the recommendation for a minimal content of<br />
linolenic acid. The oil with raised oleic and low linolenic acid gave very good results. The<br />
only production figure reported for Asoyia was about 10,000 tonnes in 2009.
85<br />
Peanut oil<br />
Peanut oil has long had the reputation of being excellent as frying oil for snack foods.<br />
However, some cultivars of peanuts are being grown commercially in the USA in which<br />
oleic acid content is increased and the linoleic acid decreased.<br />
Standard oil typically has 53% oleic acid and 27% linoleic acid and, in addition, the saturated<br />
long chain acids arachidic (0.5%), behenic (2.5%) and lignoceric (1.0%), with 20, 22 and 24 carbon<br />
chains respectively. High oleic cultivars have 76-81% oleic acid and only 3-5% linoleic acid.<br />
The modified oil is more stable to oxidation but the linoleic acid content is too low for optimum<br />
'fried' flavour development. Behenic and arachidic acids are unique fatty acids occurring<br />
in peanut oil.Their nutritional implications at high levels of consumption are still unclear.<br />
Cottonseed oil<br />
Standard cottonseed oil contains 28% saturated acids (mostly palmitic), 17.5% oleic acid<br />
and 52-56% linoleic acid. One strain has been produced in Australia with 77% oleic acid,<br />
the increase being mainly at the expense of the linoleic acid content.The oil is more suitable<br />
for frying.<br />
Other oils<br />
Modified oils have been produced from three other commercial oilseed crops but are not<br />
yet commercialised as far as can be ascertained.Their compositions are given in Table 4.<br />
The modified corn oil and safflower oil fit the ideal specifications for frying oil. Neither of<br />
the modified linseed oils is good for frying, one with still too much linolenic acid and the<br />
other with high linoleic acid content.
86<br />
It may be concluded, therefore, that palm oil and palm olein will meet growing competition<br />
from other oils, despite higher cost.The latter have the advantage that they can be grown<br />
in a wide range of temperate climates.<br />
One practical way of improving the properties of palm olein has been demonstrated in a<br />
project carried out at the Malaysian <strong>Palm</strong> <strong>Oil</strong> Board. A good quality palm olein was interesterified<br />
with methyl oleate.The product was fractionated to give a new olein with Iodine<br />
Value of 81 and a cloud point of -1.5C.The oil had oleic acid (60.5), linoleic acid (16.0%)<br />
and saturated acids (22.6%), quite comparable with the liquid oils.<br />
Blended oils<br />
Blended oils provide the best cost-benefit opportunity to produce frying oil with optimised<br />
fatty acid composition. Such blends can be made with two or more commodity oils.<br />
Work has been reported from Iran on two-component blends of palm olein with rapeseed<br />
(canola) oil, olive oil and corn oil, and on three-component blends of canola/palm<br />
olein/olive and canola/palm olein/corn oil. In each case canola was 75% of the blend.The<br />
frying performance of the blends was superior to that of canola, especially the 3-component<br />
blends. In India coconut oil was blended with sesame or palm olein. The latter had<br />
the better frying performance.<br />
In most cases, it has been demonstrated that palm oil and/or palm olein could be one of<br />
the major components, blended with any of the commodity seed oils that are otherwise<br />
limited in their usefulness for use as frying fats. The palm oil component significantly<br />
improves the keeping properties of the blends and the proportions can be adjusted to give<br />
the desired clarity during storage.
87<br />
CHAPTER 10: LOW TRANS FATS FORMULAE<br />
It is useful to bring together the low trans fats formulae proposed earlier, with new published<br />
studies relating to a wide range of food products.<br />
The product formulae that will be discussed have met the laboratory test for functionality<br />
and in some instances have been adopted for manufacture. However, they may<br />
well require minor modification for specific market requirements. In any case, they<br />
should properly be submitted to a test market, as would normally be done for any new<br />
product.<br />
The physical characteristics of palm oil products are shown in Figure 2, Chapter 6 with<br />
those of butterfat for comparison. It is apparent that palm oil products are suitable as major<br />
components of food fats.<br />
<strong>Palm</strong> stearin is an ideal high melting component (of zero trans fats content) to provide consistency<br />
in place of hydrogenated oils. The process of interesterification is often the best<br />
way to incorporate palm stearin in a blend with other oils. By the use of high temperature<br />
and a catalyst, the fatty acids become detached from the glycerol backbone of the fat molecule<br />
and re-attached in a random manner.<br />
For example, if palm stearin is reacted together with a suitable proportion of soybean oil,<br />
a semi-solid fat results with a consistency similar to butter.The change in physical behaviour<br />
is illustrated in Figures 1 and 2 on page 87, which relate to a practical application using palm<br />
stearin and palm kernel olein.<br />
BAKERY SHORTENINGS<br />
1. The Malaysian <strong>Palm</strong> <strong>Oil</strong> Board (MPOB) has processed on a pilot scale a number of zero<br />
trans fats shortenings. In each case, the performance was assessed by comparison in a<br />
standard cake-baking test with a high quality commercial shortening. Some trans-free<br />
shortening formulae are given in Table 3, Chapter 4.<br />
2. Workers in Denmark have published formulae for a conventional and a liquid shortening<br />
for cakes (Table 1).
88<br />
3. Belgian workers have proposed an interesterified blend of 30 parts soybean oil with 70<br />
parts of palm stearin (melting point 55.5°C, Iodine Value 34.8) as a basis for margarine<br />
and also shortenings.<br />
4. <strong>American</strong> workers have been accustomed to formulating mainly with various grades of<br />
hydrogenated soybean oil, which result in high trans fats content. Several methods for<br />
reduced or zero trans fats products have now been proposed:<br />
• The use of a hard stock of 50% fully hydrogenated (therefore zero trans) soybean<br />
oil interesterified with 50% soybean oil: When this hard stock was blended with an<br />
equal quantity of soybean oil, the resulting shortening had a solid content profile<br />
close to commercial products. However, no practical baking tests have been<br />
reported.<br />
• Blends with suitable properties for a bakery shortening were obtained by<br />
interesterifying 15 parts fully hydrogenated soybean oil with rapeseed oil and palm<br />
stearin (melting point 53.7°C) in various proportions.<br />
• 71% rapeseed oil and 29% stearic acid were interesterified: 52 parts of this were<br />
blended with 33 parts palm mid-fraction and 15 parts cottonseed oil.This blend<br />
was made into margarine which was comparable with two products in the market.
89<br />
• Partly hydrogenated oils were prepared by a special process which gave lower<br />
trans fats content. Canola, soybean, safflower and sunflower oils were used. Some<br />
hydrogenation was done with a conventional nickel catalyst, followed by a second<br />
step using a special platinum catalyst.When blended with soybean oil to get a solid<br />
fat content (SFC) suitable for spreads and also shortenings, the product had trans<br />
fats content of 2% or less.<br />
• 25% fully hydrogenated soybean oil interesterified with 75% palm oil, alternatively<br />
80% soybean oil interesterified with 20% fully hydrogenated soybean oil: The<br />
products are diluted with 20 parts soybean oil for tub margarine.<br />
5. Canadian workers interesterified 40% palm stearin with 60% palm kernel olein.These are<br />
both the less valued products of the respective fractionations. Figure 1 shows the SFC
90<br />
profile before - and Figure 2 after - interesterification.The undesirable long 'tail' of the<br />
blend, which would give poor eating properties, has been eliminated.<br />
6. An approach similar to the Canadian example has been to interesterify palm stearin with<br />
palm kernel oil.<br />
MARGARINE AND SPREADS<br />
Some trans-free margarine formulae are given in Table 2, Chapter 6.<br />
In recent years the market for spreadable fats has moved strongly towards reduced-fat<br />
spreads. The MPOB has published some suitable formulae. For soft blends suitable for<br />
plastic tubs the range of 25-50% palm oil with 75-50% sunflower oil is suitable. For packets,<br />
formulae within the range of 80-75% palm oil, 10-15% sunflower oil and10-0% palm<br />
kernel oil are recommended. Similar blends using interesterification also have the right<br />
properties.<br />
In Chapter 1, we indicated that the practical approach to obtaining low and zero trans<br />
products is by incorporating either palm stearin or fully hydrogenated liquid oil, often coupled<br />
with interesterification.This approach is now being adopted very widely.<br />
VANASPATI<br />
Vanaspati was developed in India in 1930 as a substitute for butterfat ghee. It was made<br />
from partially hydrogenated groundnut oil and cooled so that it crystallised in large granules<br />
with little free oil, to simulate the character of butterfat ghee.<br />
Analyses from India, Pakistan and Iran in the 1980s indicated a high trans fats content of<br />
30-50%. A high level of palm oil in vanaspati can substantively reduce or even eliminate<br />
trans fats.<br />
In India, little palm oil is used in vanaspati. A recent analytical survey revealed levels of<br />
23.3% and 23.7% trans fats in two popular brands.These results received adverse comment<br />
in the Indian press.The country's labelling regulations only require a declaration of<br />
the range of trans fats content. In one case, 8-33% is declared which is not very helpful<br />
to the consumer.
Indian workers have proposed two trans-free blends incorporating palm-based products<br />
(Table 2).<br />
91<br />
The granular crystals desired are readily obtained in interesterified blends, as shown in Table 3.<br />
Low and zero trans fats vanaspati formulae currently in use in Pakistan are detailed in<br />
Chapter 6.<br />
INDUSTRIAL FRYING<br />
Industrial frying in restaurants and snack food factories requires oil with good resistance to<br />
high temperature. Partly hydrogenated oils have been widely used in preference to liquid<br />
oils, and inevitably there is a significant content of trans fats. As an alternative, palm oil provides<br />
the required high temperature stability naturally. Annually, at least 10 million tonnes<br />
are used worldwide.<br />
A particular application is in doughnut frying.The cooked product is given a sugar coating.<br />
If liquid oil is used the coating falls off; therefore, hydrogenated oil is often specified by the<br />
manufacturers of large-scale equipment. Experience has shown that palm oil has the necessary<br />
properties to ensure satisfactory adhesion of sugar.
92<br />
MINOR USES OF PALM OIL<br />
Peanut butter<br />
To prevent oil separation during storage of peanut butter, manufacturers add about 2% of<br />
partly hydrogenated vegetable oil.This is now often replaced by a similar quantity of a hard<br />
grade of palm stearin (zero trans fats).<br />
Dried soups<br />
The fat traditionally used in dried soup powders was beef fat.This was changed to partly<br />
hydrogenated vegetable oil to avoid the cholesterol content and achieve good storage life.<br />
<strong>Palm</strong> oil is now the preferred (zero trans fats) ingredient; where long-term storage is<br />
required, partly hydrogenated palm oil is used (melting point 40-42°C), providing a low<br />
trans fats option.<br />
Pastry mix<br />
The product consists of a flour-and-fat mix packed as a free flowing powder for home<br />
use. Hydrogenated vegetable oil has been replaced by palm oil or palm oil blended with<br />
10-15% palm stearin. By chilling the fat and the flour and using an appropriate mixing<br />
machine, a free flowing powder is obtained. The user only has to mix in water and roll<br />
out the dough.<br />
While commercial concerns do not usually reveal their formulae beyond the legal labelling<br />
requirements, it is clear from the many reports of development work that reformulation<br />
with palm-based products is a favoured practice towards low trans fats content. This is<br />
borne out by the high levels of palm-based imports by Europe and increasing intake by the<br />
USA. Adverse publicity in the USA from 1986 onwards had reduced palm oil use in foods<br />
to near zero at one time.<br />
For those who do not have the resources to formulate trans-free products from scratch,<br />
a number of suppliers in the USA, Europe and Malaysia offer blends of suitable hard stock<br />
or finished product.These are mainly but not exclusively based on palm-based products.<br />
One refiner in the USA specialises in supplying palm-based products to the domestic<br />
industry.
93<br />
CHAPTER 11: PALM-BASED OLEOCHEMICALS<br />
The production of chemicals from palm oil and palm kernel oil (PKO) is attractive because<br />
the great variety of end products has much higher added value than the commodity oils<br />
themselves.<br />
At the time that Malaysia first ventured into the oleochemical industry in the late 1970s the<br />
industry was mainly located in the USA,Western Europe and Japan. Comments were made to<br />
the effect: 'Why do you want to do that? We already have plenty of capacity'. Nonetheless the<br />
Malaysian industry grew with encouragement from the government and has taken a significant<br />
share of the world market. Malaysia's exports to key destinations are shown in Table 1.<br />
In many products there is direct competition from petrochemicals, but the oleochemicals<br />
have advantages.They are from renewable resources and are much more easily biodegradable<br />
and therefore environmentally friendly.These assets have become much more important<br />
in recent years.<br />
It is estimated that 14% of all oils and fats are available for non-food use.The oleochemicals<br />
market has been growing at 2-3% a year. Malaysia, for example, exported 2.17 million<br />
tonnes of oleochemical products in 2009 (Table 2).<br />
This chapter 1<br />
describes the most important chemical steps to higher value products, and<br />
lists some of the many applications of palm-based oleochemicals.<br />
1<br />
The author acknowledges the collaboration of Prof RJ Hamilton in the preparation of this chapter.
94<br />
THE BEGINNING<br />
The 'splitting' of oils has been described as the 'gateway' to oleochemicals. Splitting was<br />
first achieved with the use of alkali, resulting in the formation of soap and glycerol. Soap was<br />
most likely the first oleochemical made by man, using wood ash from a bonfire as the<br />
source of alkali.This primitive process is still carried on in remote Nigerian villages (Figures<br />
1 to 3).
95<br />
Soap is a worldwide commodity for personal and laundry use. Good quality toilet soap is<br />
formulated with 75-80% of palm stearin or tallow and 20-25% of PKO or coconut oil.The
96<br />
long chain fatty acids give foam stability, while the shorter chain acids of the lauric oils<br />
impart good lathering and detergency. The world market for soap is over 10 million tonnes<br />
a year, with Malaysia having supplied 381,448 tonnes in 2009.<br />
In the industry today, fats are split very efficiently using a catalyst with water under high<br />
pressure (50-60 kg/cm 2 ) and temperatures around 260°C (Figure 4).The glycerol is separated<br />
and concentrated, forming a valuable by-product.<br />
The fatty acids may then be distilled to various levels of purity and marketed as such.<br />
Alternatively they are further processed, as outlined in Scheme 1.
97<br />
Fatty acids<br />
The saturated fatty acids can be made into different metal soaps. Calcium stearate is used<br />
in cattle feed. Zinc, cadmium and lead stearates are used in the rubber, paper and plastics<br />
industries.<br />
Fatty alcohols<br />
A fatty acid can be directly hydrogenated to give a fatty alcohol. Effectively the acidic group<br />
-COOH at the end of the fatty acid chain is changed into the -CH 2 OH group of the alcohol.<br />
The reaction requires a catalyst (for example, copper-chromium oxide), hydrogen at<br />
pressure (200kg/cm 2 ) and a temperature of 300°C. Alternatively the methyl esters may be<br />
hydrogenated.<br />
The fatty alcohols are the first step towards an important group of synthetic detergents,<br />
used in shampoos and washing-up liquids, among others.<br />
Long chain alcohols have also been used to form an impervious layer to reduce evaporation<br />
from water reservoirs in hot climates.
98<br />
NITROGEN COMPOUNDS<br />
The starting point for a range of nitrogen compounds is the formation of a fatty acid nitrile<br />
by heating the acid with ammonia to 300°C with a catalyst such as zinc oxide or alumina.<br />
The further reactions are shown in Scheme 2.<br />
(It should be noted that the nitrogen atom has 3 bonds available for combination, whereas<br />
the carbon atom has 4.)<br />
The nitrile<br />
(1) is hydrogenated stepwise to give first the intermediate<br />
R-CH=NH (2), the aldimine, and again to give R-CH 2 -NH 2 (3) This is a primary amine.<br />
Alternatively the intermediate (2) can be reacted with the primary amine (3) to give the<br />
secondary amine (4).<br />
If intermediate (2) is reacted with (4) we make a tertiary amine (5). All three bonds of the
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nitrogen atom have now reacted with alkyl groups. Further reaction, this time using an alkyl<br />
chloride or an alkyl bromide, gives quaternary ammonium salts (6) and (7).<br />
Product (7) is used as a disinfectant in the food industry, in breweries and in hospitals.<br />
In formulae (6) and (7), R represents a hydrocarbon chain which can be of different lengths.<br />
In product (7), for example, the reagent used in the final reaction has 14 carbon atoms and<br />
is obtained from PKO. Another quaternary, distearyl dimethyl ammonium chloride, is used<br />
in hair conditioners and fabric softeners.<br />
A quaternary is used for concentrating minerals by ore flotation.The finely milled ore<br />
is dispersed in a solution of the quaternary and air is vigorously blown through.
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The ore particles are suspended in the stable foam that forms, and so separated from the<br />
unwanted waste.<br />
Other amines are used as corrosion inhibitors, as anti-static agents in textile manufacture,<br />
as release agents in rubber mouldings and as additives in lubricants.<br />
Fatty amides are water-proofing agents.<br />
Betaines are derivatives of amino acids that occur widely in nature. Synthetic betaines are<br />
used in shampoos, bubble baths and in heavy-duty cleaning agents.<br />
Amine oxides are components of cosmetics and detergents.<br />
Primary amines can be 'ethoxylated' by reaction with ethylene oxide<br />
Ethylene oxide chains can be built up to various lengths.The products form water-in-oil or<br />
oil-in-water emulsions depending on the length of the chain (Scheme 3).<br />
Biologically active fatty acid derivatives<br />
• Methyl epoxystearate, made by oxidising methyl oleate, can be transformed in a<br />
series of reactions to give aziridine, which acts as an anti-tumour agent.<br />
• Fatty nitriles - see (1) in Scheme 2 - can be transformed into tetrazoles with antiviral<br />
activity.
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<strong>Palm</strong> fatty acids for candles<br />
Candles with good performance are obtained when double-pressed stearic acid is blended<br />
with paraffin wax in the ratio of 70:30.<br />
Sulphonated methyl esters as a detergent<br />
The methyl esters of palm stearin are fully hydrogenated and then sulphonated<br />
with sulphur trioxide (SO 3 ) to give sulphonated methyl esters (SME). Their efficiency<br />
as detergents is as good as that of the petroleum derived linear alkyl benzene<br />
sulphonates (LAS). However the SME are much more biodegradable than<br />
LAS.
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Furthermore SME are compatible with the proteolytic enzymes often added to washing<br />
powders to remove milk, egg and gravy stains, whereas LAS are not compatible. SME based<br />
on palm fatty acids are now in manufacture.<br />
Polyurethane foam<br />
Polyurethane is obtained by reacting a 'polyol', (an alcohol with many -OH groups) with an<br />
isocyanate.The latter is obtained by introducing the functional group N=C=O into toluene.<br />
Research at the Malaysian <strong>Palm</strong> <strong>Oil</strong> Board developed a process for making a polyol based<br />
on palm oil and using it in polyurethane foam.The process has been patented.<br />
Polyurethane foam can be made with flexible, semi-rigid or rigid characteristics and finds<br />
many uses in furniture, insulation of roofs and pipework, and in construction. The world<br />
market is estimated to exceed 10 million tonnes per annum, with the Asia-Pacific region<br />
absorbing one-fifth of this.<br />
Bio-diesel<br />
The transformation of a triglyceride into the methyl esters used as bio-diesel is achieved at<br />
moderate temperature with dry methyl alcohol and an alkali catalyst.<br />
In the case of palm oil, the purification of the esters also yields valuable by-products, mainly<br />
Vitamin E and carotenes.The <strong>Palm</strong> <strong>Oil</strong> Research Institute of Malaysia started a project on<br />
bio-diesel in the 1980s, built a pilot plant (Figure 7) and carried out extensive tests on road<br />
vehicles to prove the effectiveness of palm oil for this application.<br />
Bio-diesel has been promoted in the European Union with the objective of reducing greenhouse<br />
gas emissions and to provide a new market for farmers who grow rapeseed.<br />
European directives require industry to move towards the incorporation of increasing levels<br />
of bio-diesel into the fuel offered to motorists at the pump. At the time of writing, the<br />
level in the UK is 3.25%. In the USA, bio-diesel production from soybean oil has become<br />
significant.<br />
World production of bio-diesel was projected at 3,926 million gallons in 2009 and is estimated<br />
to increase rapidly.The price structure of vegetable oils has made the import of palm<br />
bio-diesel attractive and also the import of palm oil for transformation in Europe.
103<br />
USES OF OTHER FATTY ACID ESTERS<br />
Esters of medium chain fatty acids with medium chain alcohols have various uses. Myristyl<br />
myristate is a component of cosmetics, while isopropyl myristate is used in hair conditioners,<br />
lipstick and eye make-up. Glyceryl monolaurate is used in oil-in-water emulsions.These<br />
esters are sourced from PKO.<br />
A particularly interesting use of fatty acids from PKO is in the synthesis of medium chain<br />
triglycerides (MCT).The following mixture is used:
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The MCT have special nutritional properties. They are broken down in the digestive<br />
system more rapidly than fats of longer chain length. They are then transported<br />
as the free acids in the portal blood stream and rapidly digested. They are<br />
important food sources for patients who have difficulty in digesting normal fats.<br />
Owing to their rapid metabolism MCT have been proposed as energy sources in<br />
the diet of athletes.<br />
Glycerol<br />
A consequence of the production of bio-diesel is a greatly increased supply of glycerol,<br />
which has the following uses:<br />
• As a component of alkyd resins used in paints<br />
• In glyceryl monomethacrylate, which is polymerised and used in solar panels, etc<br />
• In other polymers used by dentists<br />
• In formulations of cleaners and polishes, of leather and textile processing aids<br />
• As a humectant to keep tobacco moist and also as a minor ingredient of cakes and<br />
in 'scoopable' ice cream<br />
• In the explosive nitro glycerine<br />
Potential new uses are the subject of research in a number of laboratories. A project at<br />
a US Department of Agriculture laboratory uses glycerol as feed stock for selected<br />
micro-organisms, one of which produces 'sophorolipids' of potential use in cosmetics<br />
and detergents. Other organisms produce a polymer, poly hydroxyl alkanoate (PHA).<br />
Depending on the bacterial strain used PHA, which is biodegradable, has uses in golf<br />
tees, razor handles and bottles.<br />
Cosmetic applications<br />
Products from palm oil and PKO are used in some cosmetic items (Examples 1<br />
and 2).
105<br />
Example 1<br />
Example 2<br />
The ingredient list for a skin cream includes:<br />
• Isopropyl palmitate<br />
• Triple pressed stearic acid<br />
• Glyceryl monostearate<br />
• Medium chain triglycerides<br />
• Glycerol
106<br />
CHAPTER 12: OILS AND FATS PROPERTIES<br />
The physical properties of oils and fats are basic in relation to their practical use.This chapter<br />
gives definitions of some physical properties and discusses their practical importance.<br />
Density<br />
The density of the oil is of great commercial importance because it is required for the<br />
determination of the weight of oil in shore- and ship's-tanks.<br />
Because it is impractical to physically weigh a shipment of several hundred tonnes of oil, the<br />
volume of oil is measured in tanks that have been calibrated.The weight is then calculated<br />
by multiplying by the apparent density.<br />
The formal definition is the weight of a volume of the oil at a defined temperature divided<br />
by the weight of the same volume of water at 4˚C.This is the Relative Density.The chosen<br />
temperature is 4˚C because water has its maximum density at that temperature.<br />
For practical use in determining the weight of oil in a ship's tank or a storage tank, the<br />
Apparent Density is used.The term 'litre weight in air' is self-explanatory.The measurement<br />
of the density is carried out in the laboratory and corrected to the actual temperature of<br />
oil in the tank.To obtain the weight in the tank, we need to know the volume.The empty<br />
head space in the tank (the ullage) is measured and the volume of oil obtained from a calibration<br />
chart previously prepared for the tank.<br />
The change in density for most oils is 0.00068 per degree centigrade (it is 0.00071 for the<br />
lauric oils) and therefore an error of 1°C represents 340kg of oil, quite a significant amount.<br />
Accurate temperature measurement is made by the surveyor when sampling the tank. He<br />
must make sure the tank contents are fully liquid, with no solid fats at the bottom.<br />
The sampling device is first warmed by filling and emptying it.Then samples are drawn at<br />
three levels and their temperature taken with an accurate mercury-in-glass thermometer.<br />
The sampler should not be exposed to extreme ambient temperatures during this<br />
measurement.
107<br />
Figure 1 shows a temperature measurement being made on top of a shore tank. Note the<br />
undesirable use of a copper or brass implement. Copper is a powerful catalyst for oxidation<br />
of oils.<br />
Colour<br />
The colour of oils enters into trading specifications.The standards and the trade specifications<br />
for the colour of oils use the Lovibond scale. Mr Lovibond was a brewer in the English<br />
country town of Salisbury in the 18 th century. He devised a system of pieces of glass<br />
coloured in red, yellow or blue of increasing intensity to standardise the colour of his production.When<br />
measuring red, yellow or orange colours, only the red and yellow glasses are<br />
needed.<br />
The oil in a glass cell of a standard size is placed in an enclosed box fitted with illumination.<br />
The oil colour is matched by using a suitable combination of the graded glasses. <strong>Oil</strong> colour<br />
is generally given in terms of 'Lovibond red and yellow'. A 5 1 / 4 -inch cell is used for refined<br />
oil, and a 1-inch cell for the stronger coloured crude oils. Most refined vegetable oils have<br />
a near-white colour. Refined palm oil is usually specified at a maximum Lovibond Red of 3.0<br />
in a 5 1 / 4 -inch cell.
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The strong colour of crude palm oil (CPO) is due to its content of various carotenoids<br />
(pro-Vitamin A). These are partly removed with the use of bleaching earth and partly<br />
destroyed at high temperature during refining. Experience shows that poor quality CPO is<br />
difficult - or in extreme cases, impossible - to bleach to the specified colour of 3.0.The difficulty<br />
is not due to carotene residues, but to colour formed due to deterioration of the<br />
oil.<br />
Some laboratories use an empirical bleaching test to decide what treatment is needed<br />
in the factory. A science-based measure to define bleachability of palm oil was developed<br />
by the Malaysian <strong>Palm</strong> <strong>Oil</strong> Board (MPOB) and is now part of the buying specification for<br />
CPO.<br />
It consists of measurements of colour in a spectrophotometer at two wavelengths in the<br />
ultraviolet part of the spectrum. One of these measures the carotene level. Carotene is<br />
gradually destroyed by oxidation.The second measures the increase in oxidation products<br />
of the fatty acids.The ratio of the two is a sensitive measure of the quality of CPO and is<br />
simple and rapid. It is called the Deterioration of Bleachability Index or DOBI.<br />
Another measurement of absorption, this time in the infra-red part of the spectrum, provides<br />
a measure of the trans fats content.<br />
Slip melting point<br />
The melting point of solid fats is a basic characteristic used in specifications. It is particularly<br />
useful for describing hydrogenated fats and different grades of palm stearin and palm kernel<br />
stearin.The conventional method for obtaining the melting point is described in Chapter<br />
2.An instrumental method for determining the melting point was developed by the MPOB<br />
(Figure 2).<br />
Solid fat content (SFC)<br />
The relationship of the SFC with temperature has been used in earlier chapters.The SFC<br />
is much more informative about the character of a fat than the slip melting point. An<br />
example of the marked difference between palm kernel oil - with a rapid change from<br />
hard solid to liquid - and palm oil, where the change is much more gradual, is shown in<br />
Figure 3.
109<br />
The method of measurement most widely used depends on the response of a sample<br />
to a magnetic field (the Nuclear Magnetic Resonance).The solid part of the fat responds
110<br />
differently from the liquid part. By measuring the fat brought to a range of temperatures,<br />
the familiar curves can be prepared.<br />
Cloud Point and Cold Test<br />
These two empirical measurements are used to characterise liquid oils.To determine the<br />
cloud point, a tube of the oil is placed in a refrigerated bath and the oil temperature measured<br />
at which cloudiness is first observed.<br />
The cold test involves placing a sample in an ice water bath. An oil that remains clear for<br />
5 1 / 2 hours passes the test.The test indicates the ability of the oil to remain clear when kept<br />
in a domestic refrigerator.<br />
Both tests relate to the consumer's wish for a salad or cooking oil to be sparkling clear.<br />
Standard palm olein fails to pass these tests. Double fractionation gives improved results,<br />
but these are still inferior to the more unsaturated oils.<br />
An acceptable cloud point can be obtained by blending palm olein with liquid oil as shown<br />
in Figure 4. A proportion of about 30% of palm olein is suitable. Such blends are already<br />
being marketed. Recently reported research shows that, after interesterification of palm<br />
olein with methyl oleate, the new olein matches the characteristics of liquid oils.
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Smoke Point<br />
The smoke point is of interest in oils to be used for frying.The temperature is measured<br />
while observing the steady evolution of smoke from oil being heated in an open vessel. A<br />
high smoke point is a desirable characteristic. Smaller more volatile molecules, particularly<br />
fatty acids, lower the smoke point and these increase during usage.<br />
Figure 5 shows three curves for the smoke point obtained on oils containing increasing levels<br />
of free fatty acids. Curve 1, taken from a text book, shows the effect of adding fatty acids<br />
to refined oil. Curve 2 was obtained in the same way but using a lauric oil. Curve 3 was<br />
obtained in the MPOB laboratories on used frying oils. It shows that, in addition to free fatty<br />
acids, other breakdown products also affect the smoke point.<br />
The lauric oils have a lower smoke point because of their content of the more volatile<br />
medium and short chain acids.A high smoke point limit is often specified for frying oils since<br />
it indicates a longer life in use.
112<br />
Flash Point and Combustion Point<br />
As the oil continues to be heated, smoke evolution increases until the gases can catch light<br />
and support combustion. Over-heated frying pans are a major cause of domestic fires, and<br />
are also a problem in restaurants.<br />
The flash point and combustion point are measured by heating the oil in a small closed vessel<br />
with a sliding door at the top (Figure 6).The vessel is fitted with a thermometer pocket<br />
and a stirrer. During heating, the door is momentarily opened while a flame is applied to<br />
the opening.The temperature at which the evolving gases momentarily light up is the flash<br />
point. On further heating the gases will support the flame.This is the combustion point.<br />
A modified apparatus is used for solvent-extracted oils to test that any solvent residues,<br />
which have a very low flash point, are not at a dangerous level.<br />
Polymorphism<br />
The desirability of the small crystals of the beta prime (β') formed in shortenings and margarines<br />
has been discussed in earlier chapters.<br />
The term polymorphism is applied to the existence of a triglyceride in several crystal forms.<br />
When a molten pure triglyceride is cooled quickly, the alpha (α) form is first obtained. If
113<br />
this is gently warmed it melts, but solidifies again to give the β' form. On further gentle heating,<br />
the β' form melts and re-solidifies in the beta (β) form.This is the final and stable form.<br />
The reason for this behaviour is that the rather long fatty acid chains have difficulty in packing<br />
together in the tidy structure that is a crystal.The same behaviour applies to the mixture<br />
of triglycerides that is a natural fat. Figure 8 shows the disposition of the α, β' and β<br />
forms of tristearin.<br />
Each triglyceride molecule looks like a chair, with two fatty acids facing one way and the<br />
third in the opposite direction.The fatty acids are attached to the glycerol molecule, which<br />
forms the seat of the chair, as it were.<br />
In the α form, they are stacked vertically. In the β' form, they are stacked somewhat more<br />
tightly at an angle to the vertical. The fatty acid chains are in zig-zag form, with adjacent
114<br />
chains at right angles. This is indicated in the diagram, where the middle chains zig-zag at<br />
right angles to the plane of the paper. In the β form, the fatty acids are all aligned.<br />
The different arrangement of the three forms is also evident when we look at the arrangement<br />
of the glycerides end on, in cross-section (Figure 9).<br />
In the α form, their position is rather random. In the β' form, the layers are aligned at alternate<br />
angles, whereas in the most stable beta form, they all face in the same direction and<br />
are closer together.
115<br />
Figure 10 shows how the layers of glycerides build up into a crystal. The example shows<br />
the most stable form of trilaurin with the 12-carbon lauric acid chains.
116<br />
The distance between the glycerides within the layer and the distance between the layers<br />
are measured by means of x-ray diffraction. A narrow beam of x-rays is deflected at angles<br />
determined by the spacing between the glycerides.The measurements tell us that the glycerides<br />
in the α form have the most freedom of movement, while those in the β form have<br />
the least.<br />
The melting points of the three polymorphic forms of some simple glycerides are given in<br />
Table 1.<br />
The crystallisation behaviour of cocoa butter is more complex than that of other fats. It<br />
has six polymorphic forms, of which four are unstable and readily transform into the<br />
more stable form V that is required.The main glycerides contain two saturated and one<br />
oleic acid.<br />
The final most stable arrangement arrived at is shown in Figure 11, where tristearin is<br />
compared with 2-oleodistearin.The bend at the double bond of oleic acid is accommodated<br />
in the crystal by aligning with an oleic acid from the adjacent 2-oleodistearin. So,<br />
instead of the dimension of a layer being roughly the length of two fatty acids chains, it<br />
is the length of 3.<br />
The melting points of the six polymorphs of cocoa butter are shown in Table 5, Chapter 8.<br />
Refractive Index<br />
The speed of light is lower when it is passing through a medium, such as glass, water or<br />
other liquid, than it is in vacuum. As a result a ray of light is bent at an angle in the medium.The<br />
ratio of the speed of light in a vacuum to that in the medium is the refractive index
117<br />
(RI) of the medium. It is also the ratio of the sine of the angle of incidence to the sine of<br />
the angle of refraction.The RI varies with the temperature.<br />
The measurement is made in a refractometer where the sample is placed between glass<br />
prisms, which are maintained at a constant temperature by water circulated through a<br />
jacket.<br />
The RI varies somewhat depending on the wavelength of light and this is conveniently controlled<br />
in the laboratory by using a sodium lamp, which has a strong yellow line called the<br />
D line in its spectrum.
118<br />
The RI also varies with the chain length of the fatty acids and their unsaturation and it<br />
therefore has some value as an identity characteristic. It is listed in Codex Alimentarius and<br />
other standard specifications, though for identification purposes it is somewhat outdated.<br />
However, it is used for control of the hydrogenation process. The measurement is very<br />
rapid and can be easily carried out close to the plant in the factory, or a continuously<br />
recording refractometer can be fitted on the hydrogenation vessel.<br />
A change of 0.00116 in the RI is equivalent to 10 units of Iodine Value, and the accuracy of<br />
measurement enables a change of one unit of Iodine Value to be observed.This is sufficient<br />
for most purposes.<br />
It may be noted incidentally that, due to the need to minimise trans fats, hydrogenation is<br />
much less practised than it was. Hydrogenation is now often used to saturate all double<br />
bonds, so producing a zero trans fat which is then used by interesterification with oils to<br />
produce consistent fats.