Food Chemistry

1.4 Proteins 85

Table 1.41.Amino acid composition of various plas-
teins (weight-%)

123456

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;


2. Lys-plastein; 5) Ac-Lys-plastein; 6) Control without
   addition of amino acid ethyl esters.

Table 1.42.PER-values for various proteins and plas-
teins

Protein PER value (rats)

Casein 2. 40
Soya protein (I) 1. 20
Plastein SWa+I(1:2) 2. 86
Plastein-Metb+I(1:3) 3. 38

aFrom hydrolyzate I and wool keratin hydrolyzate.
bFrom hydrolyzate I and Met-OEt. PER (cf. 1.2.5).

Fig. 1.53.Protein enrichment with sulfur amino acids
applying plastein reaction. (according toYamashita
et al., 1971)

Fig. 1.54.Amino acid patterns of some proteins

and their corresponding plasteins. (according toArai

et al., 1978)

Fig. 1.55.Soy globulin enrichment with glutamic

acid by a plastein reaction. (according toYamashita

et al., 1975)

apH 1. 6

bPartial 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

Soya protein has a pronounced solubility mini-

mum in the pH range of 3–6. The minimum is

much less pronounced in the case of the unmod-

ified 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).