Seiichi Hiratsuka

Fatty acid compositions in muscles of wild and cultured ocellate puffer Takifugu rubripes

Lipid contents and fatty acid compositions were compared among 110 muscle samples of Japanese wild, Japanese cultured, and Chinese cultured ocellate puffer Takifugu rubripes. The effects of diet on muscle lipids in cultured ocellate puffer were also investigated. There was no noticeable difference between the wild and cultured fish with regard to the lipid content, but there were significant differences in the fatty acid composition ratio such as C16:0, C16:1n-7, and C20:4n-6. Moreover, the percentages of the fatty acids C18:2n-6 and C22:5n-3 were correlated with those in the diet. These results suggest that the muscle lipid content was not affected by diet, whereas fatty acid composition was affected. There were significant differences in fatty acid composition among Japanese wild fish, Japanese cultured fish, and Chinese cultured fish. The results suggest that the fatty acid composition is applicable as a tool to distinguish between wild and cultured ocellate puffer as well as those cultured in Japan and China.

Phospholipase A1 activity of crude enzyme extracted from the ovaries of skipjack tuna

The phospholipid class composition, fatty acid composition and phospholipase A1 (PLA1) activity from the ovaries of skipjack tuna were compared with those of six other species of marine fish. In the skipjack ovaries, the lysophosphatidylcholine (LPC) proportion for the phospholipid, the docosahexaenoic acid (DHA) percentage for the total fatty acids of the phospholipids and the PLA1 activity of the crude enzyme were the highest among those of the seven species. The optimum pH and temperature for the PLA1 activity of the crude enzyme from the skipjack ovaries were in the range of pH 6–7 and 20–30°C, respectively, and calcium ions were not required. As a substrate, phosphatidylcholine was more easily hydrolyzed than phosphatidylethanolamine by this enzyme, and the plasmalogen-type phospholipid was much lower than the acyl-type phospholipid. After a 6-h hydrolysis reaction of the purified phospholipid extracted from the mixed ovaries of skipjack and yellowfin tuna by this enzyme, the LPC ratio of the phospholipid increased from 20 to 72.6% and the percentage of DHA for the total fatty acids of the phospholipid also increased. Thus, skipjack ovaries might possibly be used as a source of PLA1.