Nutritive and Health Attributes of Dairy Ingredients 403Some miscellaneous bioactive factors are
being discovered. Specifi c proteins for
binding vitamin B 12 , folic acid, and ribofl avin
may assist in enhancing bioavailablity from
milk and other foods. A fat globule mem-
brane protein called butyrophilin is a part of
the immune system. Other growth factors in
milk may help gut repair after radiation or
chemotherapy.
Whey Proteins
Whey proteins, also called serum proteins,
provide an excellent balance of essential
amino acids. The amino acid profi le resem-
bles that of skeletal muscle, making them
effective in stimulating protein synthesis in
adult muscle. Thus, they preserve muscle
mass and enhance health. Whey proteins also
enhance fat loss. Whey proteins contain more
branched - chain amino acids than any other
protein, which are metabolized (to generate
energy) in the muscle rather than in the liver.
This property makes them suitable for use by
endurance athletes such as marathon runners.
In general, whey proteins enhance humoral
immune response. The sulfhydryl - containing
amino acids cysteine and glutathione are
related to immune response. The branched -
chain amino acids stimulate muscle gluta-
mine synthesis, which is involved in immune
function. Glutathione formation is facilitated
by the high cysteine content of whey pro-
teins, which in turn controls signifi cant anti-
oxidant defenses and immune function in the
body.
Whey proteins are especially rich in cys-
teine. β - lactoglobulin contains 33 mg of
cysteine/g protein, while α - lactalbumin and
bovine serum albumin contain 68 and 69 mg
cysteine/g protein, respectively. The – SH
compounds are also involved in quenching
toxic free - radicals.
In sports nutrition, the high content of
arginine and lysine amino acids of whey pro-
teins may help in stimulating release of
growth hormones, leading to an increase in
muscle mass and a decline in body fat.
Furthermore, glutamine protects the immune
system from decline caused by overtraining.
Whey proteins consist of β - lactoglobulin
and α - lactalbumin, bovine serum albumin,
immunoglobulins (mainly IgG1, IgG2, and
IgM), lactoferrin, proteose - peptone, and a
number of diverse enzymes.β - Lactoglobulin
β - Lactoglobulin, a major whey protein of
milk, displays the presence of four genetic
variants. In addition to the two genetic vari-
ants A and B, variants C and D also have been
reported. β - lactoglobulin is rich in sulphur
amino acids, containing fi ve cysteine resi-
dues. It exists as a dimer linked by 1 – 3 disul-
fi de bonds. β - lactoglobulin is a fairly heat
labile protein. It stimulates lipolysis and
thereby generates rancidity. It also acts as a
carrier of vitamin A. The large numbers of
lysine residues can result in lactosylation and
accompanying changes in the physical prop-
erties of the protein.α - Lactalbumin
α - lactalbumin is a major protein in human
milk, but in cow ’ s milk it is second in pre-
ponderance to β - lactoglobulin. Three genetic
variants are reported, but the milk of western
cows only contains variant B. This protein is
rich in tryptophan and the sulphur amino
acids cysteine and methionine. There are four
disulfi des in the molecule, and it exists as a
monomer. α - lactalbumin has 54 amino acid
linkages identical with the enzyme lysozyme.
It is a glycoprotein as well as a metallopro-
tein. One mole of calcium is bound to each
protein molecule, which confers heat stabil-
ity on α - lactalbumin. This protein has a
physiological role in the synthesis of lactose
in the mammary gland. It is a component of
lactose synthetase along with uridine
diphosphate - galactosyl transferase, catalyz-
ing the transfer of galactose to glucose to
form lactose.
α - lactalbumin is a calcium - binding pro-
tein, thereby enhancing calcium absorption.