Handbook of Food Science and Technology 3

Table 1.2.
 Fatty acid composition of milk and distribution on 
 the three positions of glycerol (adapted from [CHR 95]) 
Milk fat is characterized by: 
– a high proportion of short-chain fatty acids (chain lengths of four to ten 
carbons) synthesized from acetate and 
β
-hydroxybutyrate produced by 
microorganisms during cellulose degradation in the rumen. These fatty acids 
are preferentially in the Sn3 position of triacylglycerols. They are easily 
released by the action of microbial or milk lipases, and are actively involved in 
the flavor of dairy products due to their volatility at acidic pH;
– a high proportion of saturated fatty acids (with 14, 16 and 18 carbon 
atoms), some of which come from the hydrogenation in the rumen of 
unsaturated fatty acids originating from food;

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From Milk to Dairy Products 7 
– unsaturated fatty acids from either the diet or the desaturation of saturated 
fatty acids by 
Δ
9-desaturase in epithelial cells;
– unsaturated fatty acids whose double bonds are in 
trans
configuration 
and/or are conjugated resulting from the hydrogenation of fatty acids in food 
by microorganisms;
– the presence of bacterial fatty acids (fatty acids with odd numbers of 
carbons, branched-chain fatty acids). 
Fatty acids determine the physical properties of fat (melting point, 
crystallization properties) by the length of their carbon chain, their level of 
unsaturation and their position on the glycerol molecule. Milk fat has a
broad melting profile that varies throughout the year, mainly due to diet.
At -30°C, milk fat is completely solid and at 40°C it is completely liquid. 
Between these two temperatures, liquid fat, located mainly in the core of the 
globule, and solid fat, forming a solid shell located at the periphery of the 
globule, coexist. 
1.1.1.2.
 Milk fat globule membrane 
The milk fat globule membrane (MFGM) accounts for 1 – 2% (w/w) of 
total lipids. It is primarily composed of proteins (butyrophilin, xanthine 
oxidase, several enzymes, etc.), phospholipids (phosphatidylethanolamine, 
phosphatidylinositol, 
phosphatidyl-serine, 
phosphatidylcholine, 
and 
sphingomyelin), neutral lipids (triacylglycerol) and a small proportion of other 
components (cholesterol, cerebrosides, 
β
-carotene, etc.). Its structure is closely 
linked to the mechanisms involved in the formation of lipid droplets in 
secretory cells and to their method of secretion in the alveolus of the 
mammary gland. It is composed of an inner layer of proteins and polar lipids 
from the endoplasmic reticulum, allowing the lipid fraction to be dispersed as 
lipid droplets in the cytoplasm of secretory cells. These lipid droplets, when 
secreted, are surrounded by the phospholipid bilayer membrane of secretory 
cells (Figure 1.2). A portion of the cytoplasm from the secretory cells can be 
trapped in the MFGM. The membrane is typically around 40 nm thick. The 
MFGM is composed of lipid rafts, consisting of rigid domains rich in 
sphingomyelin, which move in a continuous bilayer made of the other 
phospholipids. The size of the lipid rafts depends on the temperature and time 
of milk fat globule handling.

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8 Handbook of Food Science and Technology 3