Handbook of Food Science and Technology 3

Table 1.5.
 Average physicochemical properties of casein
micelles at 20°C and pH 6.7 (modified from [MCM 84]) 
1.1.3.3.
 Whey proteins 
Whey proteins are defined as the protein fraction that remains soluble at pH 
4.6. 
β
-lactoglobulin, 
α
-lactalbumin, bovine serum albumin (BSA), 
immunoglobulins and lactoferrin represent more than 90% of all whey 
proteins. They are mostly globular proteins with a high sensitivity to heat 

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14 Handbook of Food Science and Technology 3 
treatment. They are generally rich in sulfuric amino acids and tryptophan 
residues making them highly nutritious.
β
-lactoglobulin has a molecular weight of 18.3 kDa and its concentration in 
cow’s milk ranges from 0.2 to 0.4% (w/w). Its biological function is still 
unknown. There are several genetic variants of 
β
-lactoglobulin, but types A 
and B are the most common. Its secondary structure consists primarily of two 
perpendicular 
β
-sheets forming a central hydrophobic cavity held in place by 
two disulphide bridges and partially closed by an 
α
-helix. The cavity can hold 
a small hydrophobic molecule, which can be a fatty acid, retinol or an 
aromatic molecule. In addition, 
β
-lactoglobulin has a free cysteine residue 
naturally buried in the protein core, which upon input of energy (e.g. heat) is 
exposed to the solvent and can initiate intermolecular exchange reactions. 
β
-
lactoglobulin has a pI of 5.2 and its quaternary structure varies depending on 
pH. Under physiological conditions (pH 6.8), 
β
-lactoglobulin exists mainly in 
the form of non-covalent dimers.
α
-lactalbumin has a molecular weight of 14.1 kDa and a pI of 4.5. Its 
concentration in cow’s milk ranges from 0.1 to 0.15% (w/w). The secondary 
structure of 
α
-lactalbumin consists of four 
α
-helices and a 
β
-sheet; its tertiary 
structure is stabilized by four disulphide bridges and the presence of one 
calcium ion at a specific site on the protein. The affinity of 
α
-lactalbumin for 
calcium and its conformation are highly dependent on pH. A drop in pH below 
4 induces protonation of carboxylic groups involved in the coordination of 
calcium, which results in the release of calcium. 
α
-lactalbumin contributes to 
the regulation of galactosyltransferase activity in the synthesis of lactose.
BSA is present in cow’s milk at a concentration of between 0.01 and 
0.04% (w/w). Its molecular weight is 66 kDa and it has the distinction of 
having 35 cysteine residues, 34 of which are involved in intramolecular 
disulphide bridges. It has an ellipsoidal shape and its surface is comprised of 
hydrophobic pockets allowing the attachment of long-chain fatty acids.
Immunoglobulins are present in cow’s milk at a concentration of 0.06 – 
0.1% (w/w). Their pI is within a pH range of 5 – 8. They are glycoproteins 
derived from blood and have antibody properties. They are synthesized in 
response to stimulation by antigens. Immunoglobulins are comprised of two 
types of polypeptide chains, a light chain with a molecular weight of about
28 kDa and a heavy chain of about 50 – 70 kDa. The basic structure of

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From Milk to Dairy Products 15 
immunoglobulins, the molecular weight of which is close to 160 kDa, consists 
of four subunits linked by disulphide bonds. Each subunit differs in its amino 
acid sequence at the N-terminus, which gives the subunits immunological 
specificity.
Lactoferrin has a molecular weight of 75 kDa and a pI of 8.5. Its tertiary 
structure is stabilized by 16 disulphide bridges. It has two free cysteine 
residues. A molecule of lactoferrin has the ability to bind two iron ions in the 
presence of a synergistic anion (carbonate under physiological conditions). 
Affinity to iron is high at neutral or basic pH (stabilization of iron in basic 
medium), but iron is quickly released in acid medium. Its iron chelating 
property gives lactoferrin antimicrobial activity.