Properties and Mchanisms of Lipid Peroxidation in Fish Skin

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The heat-labile prooxidant substances were extracted an from fresh sardine(Sardinops melanosticta)skin tissues to elucidate the lipid oxidation mechanisms in sardine skin where the specific fishy odors are generated quickly after catch.The chromatography on several columns gave a prooxidant peak with a typical absorption spectrum of heme protein. This peak gave a single band on SDS polyacrylamide gel electrophoresis. The molecular weight was estimated to be approximately 18000 daltons.This prooxidant substance. oxidized exclusively polyunsaturated fatty acids with Z, Z-1, 4-pentadiene structure. However, not only free fatty acids but ester lipids such as triacylglycerols were oxidized efficiently. The analysis of oxidation products from linoleic acid revealed the high selectivity of the reaction which primarily gave 13(S)-hydroperoxide among 8 possible hydroperoxide isomers. These results showed that the prooxidant in sardine skin is a heme-containing lipoxygenase. The involvement of this enzyme in fishy odor generation was suggested because the hydroperoxidelyase activity to form hexanal from linoleic acid was found in the enzyme.