390 Chapter 16
- Glycomacropeptides from κ - casein
- Phosphopeptides and caseinomorphins
derived from caseins - Immunomodulating peptides
- Platelet - modifying peptide
- Angiotensin - converting enzyme (ACE)
inhibitor peptide (lowers blood pressure) - Calmodulin - binding peptides
- Bactericidal peptides from lactotransferrin
(Otter, 2003 ).
Both caseins and whey proteins of milk
possess physiological and biological proper-
ties. The biological properties of milk pro-
teins are summarized in Table 16.13.CaseinsCaseins are divided into α (^) s1 - , α (^) s2 - , β - , and
κ - fractions, which, along with the whey pro-
teins β - lactoglobulin and α - lactalbumin, are
gene - derived proteins synthesized in the
mammary gland. All of these proteins are
heterogeneous and exhibit genetic poly-
morphs. There are two to eight genetic vari-
ants differing from each other in one to 14
amino acids. The variants may have an
impact on the protein concentration and func-
tional properties of milk. The γ - fraction orig-
inates from β - casein by the effect of the
native proteolytic enzyme of milk.
Caseins display distinctive structure,
charge, physical, and biological properties as
well as a nutritional role. The interaction of
various caseins and calcium phosphate con-
tributes to the formation of large colloidal
complex particles called casein micelles.
Hydrophobic interactions with calcium phos-
phate and sub - micelles seem to be involved
in the formation of micelles. Micelle compo-
sition consists of 63% moisture and the dry
matter consists of 92% to 94% protein and
6% to 8% colloidal calcium phosphate. Other
associated salts are magnesium and citrate.
The caseins are phosphorylated proteins,
containing one to 13 phosphoserine residues.
The major proteins of milk are casein and
whey proteins in the ratio of 80:20. Casein
further consists of various fractions including
α (^) S1 - casein and α (^) S2 - casein, β - casein, and κ -
casein (Table 16.12 ). Also shown are the
major whey proteins of milk.
A number of proteins found in milk are
now recognized for their physiological activ-
ity, including immunoglobulins, lactoperoxi-
dase, lactoferrin, folate - binding protein,
insulin - like growth factors (IGF - 1 and IGF -
2), mammary - derived growth factors
(MDGF - I and MDGF - II), transforming
growth factors (TGF α 1 , TGF α 2 , TGF β ), fi bro-
blast growth factors, and platelet - derived
growth factors. Peptides derived from milk
proteins are gaining recognition for their bio-
logical and functional roles. For example,
evidence points to physiologically active:
Table 16.3. Contribution of nutrients by dairy
products (except butter) to the United States
per capita food supply of nutrients in 2005.
Nutrient Percent
contribution
Energy 7.6
Fiber 0.4
Protein 18.1
Fat 8.3
Saturated fatty acids 16.6
Monounsaturated fatty acids 5.2
Polyunsaturated fatty acids 1.3
Cholesterol 12.5
Carbohydrate 4.3
Calcium 70.3
Phosphorus 30.1
Zinc 15.0
Copper 2.5
Magnesium 13.9
Potassium 16.0
Sodium 33.2
Iron 1.8
Selenium 9.8
Ribofl avin 25.0
Vitamin A (RAE) 15.7
Vitamin B 12 18.2
Vitamin B 6 6.8
Folate 3.3
Thiamin 4.3
Ascorbic acid 2.5
Vitamin E 1.7
Niacin 1.1
Adapted from Hiza, Bente, and Fungwe (2008)