Handbook of Food Science and Technology 3

Table 1.4.
 Average composition of casein micelles in % (w/w) 
The composition of casein micelles varies slightly depending on their 
diameter, which varies between 50 and 600 nm for an average diameter of 
about 150 nm. Regardless of the size of the micelle, the proportion of 
α
S1
and 
α
S2 
casein varies marginally, whereas the ratio of 
β
- to 
κ
-caseins increases 
with the size of the micelle. Micelle organization, or the arrangement and 
distribution of the various micelle components and their types of association, 
is still a subject of intense debate. The non-charged regions of caseins form 
rigid structures maintained by hydrophobic associations and hydrogen bonds; 
colloidal calcium phosphate, in the form of nanoclusters, shields the negative

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From Milk to Dairy Products 13 
charges of phosphoserine clusters and allows the association of casein 
micelles. 
κ
-casein is structured into inhomogeneous clusters almost 
exclusively located on the micelle surface. Without phosphoserine clusters, 
κ
-
casein remains associated to the casein micelle by its hydrophobic N-terminus, 
but prevents further micelle growth. Its charged hydrophilic C-terminus 
protrudes about 5 – 10 nm into the solvent phase, making the micelle appear 
hairy.
Table 1.5 shows some of the properties of casein micelles. Their 
composition and physicochemical properties are highly dependent on the 
solvent phase.
Property Values 
Average diameter (nm) 
150 
Area (cm
2
) 
8 × 10
–10
Volume (mL) 
2.1 × 10
–15
Density (hydrated) 
1.0632 
Hydration (g H
2
O g
-1
of proteins) 
3.7 
Voluminosity (mL g
-1
of proteins) 
4.4 
Molecular weight (hydrated) (Da) 
1.3 × 10
9
Molecular weight (dehydrated) (Da) 
5 × 10
8
Water content (%, w/w) 
63 
Number of caseins per micelle 
2 × 10
4
Number of nanoclusters of calcium phosphate per micelle 
3 × 10
3
Number of micelles per L of milk
10
17
– 10
19
Mean free distance between micelles (nm) 
240 
Zeta potential (mV) 
–13