Effect of ingestion of thermally oxidized frying oil on peroxidative criteria in rats.

Thermally oxidized rapeseed oils (4 levels of deterioration; used by a manufacturer of fried fish paste in a conventional manner) were fed to rats at a practical level of concentration. Rats were fed a diet ad libitum for 13 weeks that contained 15% of a test oil. The effects of the diet on several biochemical criteria related to peroxidative alterations were investigated. In groups given thermally oxidized oils relative liver weight, relative kidney weight, thiobarbituric acid-reactive substances (TBA-RS) in the liver and reduced glutathione content were increased significantly in proportion to the degree of deterioration of the oil, compared with the group given fresh oil. Tocopherol contents in both serum and liver were decreased considerably in proportion to the deterioration level of the supplied oils. The above criteria correlated well with various deterioration indices of the oil. For instance, TBA-RS was well correlated (p less than 0.001) with petroleum ether-insoluble oxidized fatty acid (r = 0.9191), column chromatographically separated polar fraction (r = 0.9056), glyceride dimer fraction (r = 0.9023) and carbonyl value (r = 0.8647).