Effect of release of free fatty acids by enzymatic hydrolysis of phospholipids on lipid oxidation during storage of fish muscle at -5.DEG.C.

The relationship between release of free fatty acids (FFA) by lipolytic hydrolysis and lipid oxidation was studied in Pacific mackerel and carp. For this purpose, the minced ordinary muscles were stored for four weeks at -5°C, where enzymatic hydrolysis of phospholipids was the most pronounced at 0°C to -20°C. The changes in TBA number and TBA37°C-2h, susceptibility of muscle to lipid oxidation, and the changes in antioxygenic activities of extracted lipids against linolenate oxidation were followed during storage. Besides, the effect of phospholipase A2 (PLase A2) treatment on TBA37°C-2h was examined on the fresh muscles. In Pacific mackerel TBA number and TBA37°C-2h increased during storage, whereas in carp TBA number scarcely increased and TBA37°C-2h slightly decreased. However, PLase A2 treatment did not bring about any depression in TBA37°C-2h of both fresh muscles in spite of increases in FFA contents. Moreover, the antioxygenic activities of extracted lipids decreased in weight gain or in coupled oxidation of β-carotene during storage of the muscles. These results indicated that the release of FFA with PLases did not lead to an inhibition of lipid oxidation in the muscles, although there was a possibility to promote it.