Influences of freeze-thawing process on the quality of sardine and horse mackerel during refrigerated storage.

In order to obtain information concerning influences of freeze-thawing process on the quality of fish during refrigerated storage, fresh round sardine and horse mackerel were frozen at -20°C and subsequently stored at the same temperature for 35 days. After thawing in water, the fish was stored in a refrigerator of about 5°C for 8 days. During storage, VBN content, K value, TBA value, lipid class composition and fatty acid composition were determined at an appropriate interval and compared with those of the unfrozen fish which was stored under the same refrigerated conditions. As a result, it became clear that freeze-thawing process accelerates 1) deterioration of freshness in horse mackerel but not in sardine and 2) enzymatic hydrolysis of lipids in sardine and both hydrolysis and oxidation of lipids in horse mackerel during refrigerated storage. From these results, it was assumed that disruption of membranes and other tissue structures of the fish flesh due to freeze-thawing process results in acceleration of various reactions involved in the deteriorations of both freshness and lipids during refrigerated storage.