2009_Book_FoodChemistry

82 1 Amino Acids, Peptides, Proteins
Table 1.37. Emulsifying property of various proteins a
Protein
Emulsifying
Activity Index
(m 2 × g −1 )
pH 6.5 pH 8.0
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
Fig. 1.45. Hydrolysis of a reductively methylated casein
by bovine α-chymotrypsin. Modification extents:
a 0%, b 33%, and c 52%. (according to Galembeck
et al., 1977)
a Protein 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-casein a 96 17 33 27 39
PER b
Casein (10%) 2.46
Casein (10%) + Met (0.2%) 3.15
Casein (5%) + Met-casein a (5%) 2.92
a Covalent binding of methionine to ε-NH 2 groups of
casein.
b Protein Efficiency Ratio (cf. 1.2.5).
Table 1.39. Association of acylated β-casein A
Protein SD a Mono- Poly- S 0 20,w
S 1%
20,w
mer mer
(%) (%) (%) (S·10 13 ) (S·10 13 )
β-Casein A (I) – 11 89 12.6 6.3
Acetyl-I 96 41 59 4.8 4.7
Propionyl-I 97 24 76 10.5 5.4
n-Butyryl-I 80 8 92 8.9 8.3
n-Hexanoyl-I 85 0 100 7.6 11.6
n-Octanoyl-I 89 0 100 6.6 7.0
n-Decanoyl-I 83 0 100 5.0 6.5
a Substitution degree.
Fig. 1.46. Properties of modified wheat gluten. (according
to Lasztity, 1975)
1.4.6.2.2 Alkylation
Modification of protein by reductive methylation
of amino groups with formaldehyde/NaBH 4
retards Maillard reactions. The resultant methyl
derivative, depending on the degree of substitution,
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 Redox Reactions Involving Cysteine
and Cystine
Disulfide bonds have a strong influence on the
properties of proteins. Wheat gluten can be