Food Chemistry

10.1 Milk 505

Table 10.9.Amino acid sequencesaof genetic variants of bovine milk proteins

Protein Variant Frequencyb Positions of the substitutions

14–26 53 59 192
αs1-Casein A s are lacking
(199 AS) B w Ala Glu Glu
Ci Gly
Ds ThrP
Es Lys Gly
αs2-Casein 33 47 50–58 130
(207 AS) A Glu Ala Thr
B
C Gly Thr Ile
D lacking
18 35 36 37 67 106 122
β-Casein A^1 His
(209 AS) A^2 w, i SerP SerP Glu Glu Pro His Ser
A^3 Gln
Bs His Arg
Cs Ser LysHis
Ds Lys
Es Lys
κ-Casein 97 136 148 155
(169 AS) A x Thr Asp Ser
B w, i Arg Ile Ala
CHis
EGly
10
α-Lactalbumin A i Gln
(123 AS) B w Arg
β-Lactoglobulin 45 50 59 64 78 118 130 158
(162 AS) A x Asp Val
B w, i Glu Pro Gln Gly Ile Ala Asp Gln
CHis
DGln
EGly
FSer TyrGly
GMetGly
acf. Table 10.8.
bw: predominant in the western world (Bos taurus), i: predominant in India (Bos indicus, Bos grunniens), s: rare,

x: not predominant, but not rare.

Normally, κ-casein occurs as a trimer or as
a higher oligomer in which the formation of
disulfide bonds is probably involved. The protein
contains varying amounts of carbohydrates (aver-
age values: 1% galactose, 1.2% galactosamine,
2 .4% N-acetyl neuramic acid) that are bound
to the peptide chain through Thr-131, 133, 135
or (in variant A) 136. κ-Casein is separated
electrophoretically into various components that

have the same composition of amino acids, but

differ in their carbohydrate moiety, e. g., per pro-

tein molecule they contain 0–3 moles N-acetyl

neuramic acid, 0–4 moles galatose and 0–3 moles

galactosamine. Three different glycosyl residues

could be isolated, one of which has the structure

shown in Formula 10.3.