Food Chemistry

82 1 Amino Acids, Peptides, Proteins

Table 1.37.Emulsifying property of various proteinsa

Protein Emulsifying
Activity Index
(m^2 ×g−^1 )
pH 6.5pH8. 0

Yeast protein (88%) succinylated 322 341
Yeast protein (62%) succinylated 262 332
Sodium dodecyl sulfate (0.1%) 251 212
Bovine serum albumin – 197
Sodium caseinate 149 166
β-Lactoglobulin – 153
Whey protein powder A 119 142
Yeast protein (24%) succinylated 110 204
Whey protein powder B 102 101
Soya protein isolate A 41 92
Hemoglobin – 75
Soya protein isolate B 26 66
Yeast protein (unmodified) 8 59
Lysozyme – 50
Egg albumin – 49

aProtein concentration: 0.5% in phosphate buffer of

pH 6.5.

Table 1.38.Feeding trial (rats) with modified casein:
free amino acid concentration in plasma and PER value

Diet μmole/100 ml plasma

Lys Thr Ser Gly Met
Casein 101 19 34 32 5
Met-caseina 96 17 33 27 39

PERb

Casein (10%) 2. 46

Casein (10%) + Met (0.2%) 3. 15

Casein (5%) + Met-caseina(5%) 2. 92

aCovalent binding of methionine toε-NH
2 groups of
casein.
bProtein Efficiency Ratio (cf. 1.2.5).

Table 1.39.Association of acylatedβ-casein A

Protein SDa Mono- Poly- S^020 ,w S1% 20 ,w
mer mer
(%) (%) (%) (S· 1013 )(S· 1013 )

β-Casein A (I) – 11 89 12. 66. 3
Acetyl-I 96 41 59 4. 84. 7
Propionyl-I 97 24 76 10. 55. 4
n-Butyryl-I 80 8 92 8. 98. 3
n-Hexanoyl-I 85 0 100 7. 611. 6
n-Octanoyl-I 89 0 100 6. 67. 0
n-Decanoyl-I 83 0 100 5. 06. 5

aSubstitution degree.

Fig. 1.45.Hydrolysis of a reductively methylated ca-

sein by bovineα-chymotrypsin. Modification extents:

a 0%, b 33%, and c 52%. (according toGalembeck

et al., 1977)

Fig. 1.46.Properties of modified wheat gluten. (accord-

ing toLasztity, 1975)

1.4.6.2.2 Alkylation

Modification of protein by reductive methylation

of amino groups with formaldehyde/NaBH 4

retardsMaillardreactions. The resultant methyl

derivative, depending on the degree of substitu-

tion, is less accessible to proteolysis (Fig. 1.47).

Hence, its value from a nutritional/physiological

point of view is under investigation.

1.4.6.2.3 RedoxReactionsInvolvingCysteineandCystine.............

Disulfide bonds have a strong influence on the

properties of proteins. Wheat gluten can be