2009_Book_FoodChemistry

14.4 Processing of Fats and Oils 661
crude lecithin (approx. 0.25%). Diet margarines
have higher levels of emulsifiers. Skim milk
or skim milk powder suspended in water (milk
proteins, 1%; 2% in semi-fat margarine) is added
in the production of high quality retail brands of
margarine. The casein assists the action of the
emulsifiers and, together with lactose, provides
the desired browning when heated.
The aqueous phase of the margarine acquires
apHof4.2–4.5 by addition of citric and lactic
acids. This not only affects the flavor, but protects
against microbial spoilage. In addition, traces
of heavy metal ions are complexed. Margarine
also contains the aroma substances typical of
butter, which can be produced by microbiological
souring (cf. 10.2.3.2). Readily available synthetic
compounds, such as diacetyl, butyric acid, lactones
of C 8 –C 14 hydroxy-fatty acids (cf. 5.3.1.4)
and(Z)-4-heptenal,mayalsobeusedforaromatization.
Common salt (0.1–0.2%) is used to
round-off the flavor. Margarine is colored with β-
carotene or with gently refined, unbleached palm
oil. Attention is also given to maintaining the
presence of 1 mg of α-tocopherol per g of linoleic
acid. High quality products are vitaminized by
the addition of about 25 IU/g vitamin A and
1IU/gvitaminD 2 . The authenticity of margarine
is verified in some countries by an indicator substance
added to it. This is required by legislation.
Gently refined sesame oil (for its detection, see
Table 14.22) is one of these substances.
14.4.5.2 Manufacturing
Margarine is manufactured continuously by
a process consisting essentially of three steps:
• Emulsification of water within the continuous
oil phase.
• Chilling and mechanical handling of the emulsion.
• Crystallization, preserving the type of w/o
emulsion by efficient removal of the released
heat of crystallization.
The triacylglycerols should preferentially crystallize
in their β ′ -forms (cf. 3.3.1.2). The higher
melting β-forms are not desired since they cause
a “sandy” texture. The transitioin β ′ → β-form is
inhibited by addition of 1% saturated diacylglycerols.
14.4.5.3 Varieties of Margarine
The characteristic features of some varieties of
margarine are summarized in Table 14.19.
14.4.6 Mayonnaise
Mayonnaise is an “oil in water” or o/w emulsion
(cf. 8.15.1) consisting of 50–85% edible oil,
5–10% egg yolk, vinegar, salt and seasonings
(cf. 11.4.2.3). The emulsion is stabilized by egg
yolk phospholipids. Products with a lower oil
content (<50%) may contain thickening agents
such as starch, pectin, traganth, agar-agar, alginate,
carboxymethylcellulose, milk proteins or
gelatin. Sorbic acid, benzoic acid or the ethyl
ester of p-hydroxybenzoic acid are added as
preservatives. The stable emulsion is produced
in a combinator with a homogenizer and then
packed.
14.4.7 Fat Powder
In contrast to fats and oils, fat powders have better
stability against autoxidation and, in some
food products such as dehydrated soup powders
or broths, are easier to handle. They are manufactured
from natural or hardened plant fats, sometimes
with the addition of emulsifiers and protein
carriers. Butter and cream powders are also produced.
Two basic flow diagrams of the production of fat
powders are shown in Fig. 14.6.
In a cold-spray process, the melted fat is sprayed
under high pressure into a cooled (−35 ◦ C) airblast
crystallization chamber, where the fat particles
solidify. After being recrystallized, the particles
are coated to avoid clumping.
In a spray-drying process, the fat is homogenized
with emulsifiers, water and skim milk, spray dried
and subsequently crystallized.
14.4.8 Deep-Frying Fats
Traditionally, the fats used for deep frying are
those whose stability against autoxidation have