EFFECT OF UV IRRADIATION ON LIPID-PEROXIDATION IN EDIBLE FATS

Free radical reactions generated by ultraviolet light during 20 min an d 6 h treatment were investigated in soy oil, sunflower oil, olive oil , margarine and lard. The control samples were not treated. Lipid pero xidation characteristics, fatty acid composition, tocopherol and oxidi zed derivatives of cholesterol were measured. Treatment by ultraviolet light for 20 min had no detectable effect on fatty acid composition a nd tocopherol in the samples. The chemiluminescence intensity, the per oxide value and the thiobarbituric acid reactive substances increased slightly but significantly. Significant expansion of lipid peroxidatio n was found after treatment for 6 h, The concentration of free radical s measured by chemiluminometry increased significantly as a consequenc e of ultraviolet light, as well as the peroxide value and the concentr ation of thiobarbituric acid reactive substances. Tocopherols decrease d considerably in the oils and margarine. Formation of a small amount of oxidized cholesterol derivatives was observed in lard. The degree o f change in lipid peroxidation characteristics was influenced by the f atty acid composition and tocopherol content in fats. Soy oil contains about 7% linolenic acid that is oxidized hundred times faster than ol eic acid. In spite of this fact, soy oil did not show an extremely hig h sensitivity in lipid peroxidation induced by ultraviolet light, sinc e half the amount of tocopherols originally present in oil remained af ter 6 h. Strongly significant correlation was observed between chemilu minescence intensity and peroxide value, chemiluminescence intensity a nd thiobarbituric acid reactive substances (TEARS), peroxide value and TEARS in various edible fats.