Acceleration of lipid oxidation in the extract from the skin of fish.

In lipid oxidation during cold storage of fish, the authors found that TBA/kg skin of fatty fish was always higher than that of lean fish; whereas TBA/10g lipid in the skin of lean fish was frequently higher than that of fatty fish. With the purpose of finding the cause of high TBA/10g lipid in the skin of lean fish, we examined the prooxidant in the skin of fishes. The extracts from skins of Pacific mackerel and Plaice accelerated oxidation of linoleate enzymatically. The prooxidant was found to be dioxygenase which had an optimum temperature at 25°C and a pH value of 13 and required Co2+ as a stabilizer and contained Fe3+ in the molecule. The activity of dioxygenase per g of defatted skin was high in the skin of fatty fish and low in that of lean fish but the activity per g of lipid turned out to be the reversal of this order. At the same time the residual activity in the skin of lean fish was higher than that of fatty fish after the storage at -5°C. From these results, the authors concluded that the high TBA/10g lipid in the skin of lean fish during cold storage was caused by the dioxygenase.