乾燥による魚肉蛋白質の変性について

Abstract

In the previous papery1), it was shown that on dehydration of muscle of flatfish or squid, “Myosins s”** were readily denatured -the extractability decreased-, while alubumins remained unchanged. The question, however, was left open whether the proteins extractable after dehydration are the same as before. In order to answer it, the changes in viscosity and streaming birefringence (SB) of extractable proteins during dehydration process were followed, using thin slices of flatfish muscle as material. Since it was found2) that in fish “Myosin”, different from rabbit “Myosins”, viscosity number, In ηr/c (ηr: relative viscosity, c: protein concentration), is not independent to c, viscosity was determined at two protein concentrations, one above and one below 0.7mg/ml, and the result was expressed in viscosity number at concentration 0.7 mg/ml. Each determination was carried out, using the tilting viscometer2), at velocity gradients 200 and 500 sec-1. Streaming birefringence was compared by minimum protein concentration which gives a distinct cross of isocline under crossed Nicols. Results. (i) Viscosity number of salt extractable proteins (L) decreased in parallel to rate of dehydration (Fig. 1, a, b). However, one cannot safely deduce from this the change in viscosity of “Myosins” in the course of dehydration, because “Myosins” content of this fraction vividly decreased on dehydration as shown in Table 2, and because in fish “Myosins” viscosity number lowers with decreasing concentration 2). (ii) Viscosity number of Fraction S2 prepared according to the scheme shown in Table 1, was also found to decrease with dehydration (Fig. 2, a and b). “Myosin” content of this fraction kept nearly constant up to 8 day dehydration (Tables 4 and 5). Therefore, one can safely conclude the decrease in viscosity of “Myosins” with dehydration of meat. (iii) Streaming birefringences of “Myosins” decreased in the course of dehydration of meat (Tables 3 and 6). It may be concluded that dehydration causes not only decrease of extractability of “Myosins”, but also changes in shape of the particles, such as decrease in asymmetry.