魚肉たん白の冷凍変性に関する研究 : 液体窒素 (-196°C) 凍結と-20°C凍結との比較

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1 The effects of freezing With the view of the denaturation of fish muscle protein, effect of super rapid freezing by immersing fish meat in liquid nitrogen was examined with a reference sample which had been frozen at -20°C. Sea bass, carp and Alaska pollack were frozen at temperatures of -196°C (liquid nitrogen) or -20°C (see Fig. 1) and the “myosins” (a mixture of actomyosin and myosin) extracted from the muscle were examined for their physico-chemical properties. As seen in Table 3, no significant difference was observed in ultracentrifugal characteristics, viscometric behavior, ATP-sensitivity and the amounts of salt extractable proteins, between unfrozen muscle and muscle frozen in liquid nitrogen. On the other hand, there were considerable differences in the characteristics of protein from unfrozen fish and from those frozen at -20°C. Increase of the amounts of the salt extractable proteins and dependence of the viscosity of myosins solution on the protein concentration and decrease of sedimentation constant (S20) value of actomyosin were found in muscles frozen at air of -20°C (Fig. 2, 4 (b), Table 1). 2 The effects of cold storage No distinct change occured in the characteristics of “myosins” in the fish muscle frozen in liquid nitrogen, even after being stored for 1 week at -20°C, however, appreciable changes took place in samples after storage period for longer than 3 weeks at this temperature (Fig. 7, 8). When storage temperatures of -30°C or -80°C were employed, little changes in the ultracentrifugal properties were detected even after 11 weeks (Fig. 10). On the other hand, proteins from muscle frozen and held at -20°C showed drastic changes in ultracentrifugal patterns and S20 value of actomyosin after only 1 weeks storage (Fig. 7, 8). Fine ice crystals were formed inside the muscle fiber when the tissue was frozen in liquid nitrogen and stored at -20°C for 3 weeks. There were pronounced differences in the microscopic structures of tissues frozen and stored at -20°C for the same period (Plate 1). These findings suggest that super rapid freezing by means of liquid nitrogen can control protein denaturation, if sufficiently low storage temperatures (e. g. below -30°C) are used subsequently.
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魚肉たん白の冷凍変性に関する研究 : 液体窒素 (-196°C) 凍結と-20°C凍結との比較

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