2009_Book_FoodChemistry

1.4 Proteins 85
Table 1.41. Amino acid composition of various plasteins
(weight-%)
1 2 3 4 5 6
Arg 1.56 1.33 1.07 1.06 1.35 1.74
His 1.07 0.95 0.81 0.75 0.81 1.06
Ile 4.39 6.39 6.58 5.49 6.23 5.67
Leu 20.18 23.70 23.05 23.75 25.28 23.49
Lys 0.20 0.20 0.24 2.14 3.24 0.19
Phe 6.63 7.26 6.82 7.34 7.22 6.98
Thr 2.40 2.18 9.23 2.36 2.46 2.13
Trp 0.38 9.71 0.25 0.40 0.42 0.33
Val 3.62 5.23 5.77 5.53 6.18 6.20
Met 1.58 1.87 1.67 1.89 2.06 2.04
Cys 1.00 0.58 0.88 0.81 0.78 0.92
Ala 7.56 7.51 8.05 7.97 7.93 8.77
Asp 4.61 3.38 3.42 3.71 3.60 3.91
Glu 21.70 12.48 14.03 14.77 12.95 13.02
Gly 1.48 1.15 1.23 1.29 1.27 1.52
Pro 10.93 8.42 9.10 9.73 9.14 9.37
Ser 4.42 3.40 3.89 3.93 3.74 4.28
Tyr 4.73 5.35 4.97 5.00 6.08 5.54
1) Zein hydrolyzate; 2) Trp-plastein; 3) Thr-plastein;
4) Lys-plastein; 5) Ac-Lys-plastein; 6) Control without
addition of amino acid ethyl esters.
Fig. 1.54. Amino acid patterns of some proteins
and their corresponding plasteins. (according to Arai
et al., 1978)
Table 1.42. PER-values for various proteins and plasteins
Protein
PER value (rats)
Casein 2.40
Soya protein (I) 1.20
Plastein SW a +I(1:2) 2.86
Plastein-Met b +I(1:3) 3.38
a From hydrolyzate I and wool keratin hydrolyzate.
b From hydrolyzate I and Met-OEt. PER (cf. 1.2.5).
Fig. 1.55. Soy globulin enrichment with glutamic
acid by a plastein reaction. (according to Yamashita
et al., 1975)
a pH 1.6
b Partial hydrolyzate/Glu-α-γ-(OEt) 2 = 2:1, substrate
concentration: 52.5%, E/S = 1/50, pH 5.5at37 ◦ Cfor
24 h; sample contains 20% acetone
c 0.2mol/Lat25 ◦ Cfor2h
Fig. 1.53. Protein enrichment with sulfur amino acids
applying plastein reaction. (according to Yamashita
et al., 1971)
Soya protein has a pronounced solubility minimum
in the pH range of 3–6. The minimum is
much less pronounced in the case of the unmodified
plastein, whereas the glutamic acidenriched
soya plastein has a satisfactory solubility over the
whole pH range (Fig. 1.56) and is also resistant to
thermal coagulation (Fig. 1.57).
Proteins with an increased content of glutamic
acid show an interesting sensory effect: partial
hydrolysis of modified plastein does not result
in a bitter taste, rather it generates a pronounced
“meat broth” flavor (Table 1.43).