Food Lipids: Chemistry, Nutrition, and Biotechnology

the disadvantages are being reported. References 10–13 provide general information
on butter.
Butter is a water-in-oil emulsion consisting of fat (80–82%) and an aqueous
phase (18–20%). The legal limit for water is 16% and the aqueous phase also contains
salt and milk-solids-not-fat. It is made from cow’s milk (3–4% fat), which is
converted first to cream (30–45% fat) by centrifuging and then to butter by churning
and kneading. During churning there is a phase inversion from an oil-in-water to a
water-in-oil emulsion. Details of annual production and disappearance are given in
Table 6. Production of butter, which peaked in the 1980s (6.0–6.4 MMT) has now
fallen below 6 MMT but is predicted to rise steadily to 7.8 MMT in the next 20
years. The biggest consumers are in the Indian subcontinent (India and Pakistan) and
in EU-15 within which France has a consumption equivalent to more than 20% of
total oil and fat disappearance for that country (Table 5).
The composition of milk fat changes between summer and winter according to
changing dietary intake (Table 7). The fat is mainly tricaylglycerols (97–98%) along
with some free acids, monoacylglycerols, and diacylglycerols. Also present are cholesterol
(0.2–0.4%), phospholipids (0.2–1.0%), and traces of carotenoids, squalene,
and vitamins A and D.
Following several thorough examinations, cow’s milk fat is now known to
contain more than 500 different fatty acids. Most of these are present only at exceedingly
low levels but some of these, such as the lactones which provide important
flavor notes, are important. Among the many fatty acids are the following (see also
Table 7):
• Saturated acids in the range 4:0 to 18:0 including some odd-chain members.
• Low levels of iso-, anteiso-, and other branched chain acids.
• A significant level of monoene acids (28–31%) that is mainly oleic but
includes other isomers, among which are some with trans configuration.
• trans acids, produced by biohydrogenation of dietary lipids, are significant
components of all ruminant milk fats (about 4–8%). They are mainly C 16
and C 18 monoene acids of which vaccenic acid (11t-18:1) is the major
component.
• Very low levels of polyene fatty acids and even those cited as linoleic or
linolenic are not entirely the all-cis isomers.
• Trace amounts of oxo (keto) and hydroxy acids and lactones of which the
latter are important flavor components.
The fatty acid composition of milk depends on the diet of the cow, so that in
many countries there is a difference in composition between winter (fed indoors)
and summer (pasture fed), and this can be further modified by controlling the diet.
An exciting development in lipid science in recent years has been the recognition of
the importance of certain octadecadienoic acids with conjugated unsaturation (conjugated
linoleic acid, CLA), which are produced by ruminants and appear in low but
significant levels in the milk and meat of these animals. This topic is important
enough to merit a chapter of its own in this volume (Chapter 21).
The level of butyric acid at around 4% by weight may be considered insignificant,
but it should be recognized that this is equivalent to about 8.5% mol. Since
this acid is likely to occur only once in any triacylglycerol molecule (at the sn-3
position), a quarter of all the triacylglycerol molecules in butter contain butyric acid.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.