Handbook of Food Science and Technology 3

1.1. The biochemistry and physical chemistry of milk
 
Milk is a natural emulsion. Fat, which represents approximately 4% of the 
overall composition of cow’s milk (w/w), is present in the form of fat globules 
dispersed in the skimmed milk phase.
The non-fat phase of cow’s milk (skimmed milk) is composed mainly of 
water (90% (w/w) of the overall composition) in which the following are 
dispersed or dissolved: 
– lactose (4.8 – 5% (w/w) of overall composition); 
– protein (3.2 – 3.5% (w/w)); 
Chapter written by Thomas C
ROGUENNEC
, Romain J
EANTET 
and Pierre S
CHUCK
. 
Handbook of Food Science and Technology 3
:
 Food Biochemistry and Technology
, 
First Edition. Edited by Romain Jeantet, Thomas Croguennec, Pierre Schuck and Gérard Brulé.
© ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc.

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4 Handbook of Food Science and Technology 3 
– non-protein nitrogen (NPN) consisting of urea, amino acids and peptides, 
representing about 5% of the nitrogen fraction of milk; 
– inorganic minerals (calcium, phosphate, chloride, potassium, sodium) 
and organic acids (mainly citric acid in fresh milk); 
– water-soluble vitamins.
1.1.1.
 Milk fat 
The fat content of cow’s milk varies between about 3.3 and 4.7% (w/w) 
depending on breed, lactation stage, season, and so forth. Milk fat is mostly 
present in the form of fat globules measuring between 0.2 and 15 µm in 
diameter. Around 75% of fat globules are smaller than 1 µm, but they 
represent less than 10% of the total volume of milk fat. Similarly, there are 
very few fat globules larger than 8 µm; they represent less than 3% of the 
overall volume. Thus, almost 90% of milk fat is in the form of milk globules 
measuring between 1 and 8 µm in diameter. The average diameter of fat 
globules is approximately 4 µm. The core of the fat globule almost exclusively 
consists of neutral lipids, while the fat globule membrane is composed of 
complex lipids and proteins. The amphiphilic properties of these complex 
lipids and proteins facilitate the creation of interfaces and help keep the fat in 
the dispersed state (Figure 1.1).