マサバの氷温貯蔵における品質低下に及ぼす凍結・解凍処理の影響

概要

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Fresh round mackerel was frozen at -20°C, subsequently stored at the same temperature for 100 days, thawed in tap water, and stored again at -1°C for 30 days. During storage, VBN content, K value, TBA value, free amino acid composition, lipid class composition, and fatty acid composition of lipids in the white muscle of fish were determined at an appropriate interval and compared with those of the unfrozen fish which was stored under the same conditions, i.e. at -1°C. The results obtained showed that the freeze-thawing process slightly accelerated deterioration in freshness of fish during storage at -1°C. Oxidation and enzymatic degradations of lipids during storage were also accelerated by this processing during the subsequent storage. Contents of most free amino acid increased during storage, while that of histidine decreased. The rate of increase in the content of each of the free amino acids was higher in the freeze-thawed sample than in the unfrozen sample. These deterioration in the quality of freeze-thawed fish seems to be due to disruption of membranes and other tissue structures of the fish flesh caused by freeze-thawing process.