VITAMIN-E STATUS AND TISSUE FATTY-ACID COMPOSITION IN RATS FED A MODERATELY OXIDIZED SOYBEAN OIL AT LOW OR HIGH VITAMIN-E SUPPLY

This study was performed to investigate the effect of feeding a modera tely oxidized soybean oil on vitamin E status and tissue fatty acids i n rats. Therefore, growing malt: rats were fed diets containing either a mixture of coconut oil and soybean oil (19:1, w:sv), fresh soybean oil, or heated and air-treated soybean oil as sources of dietary fats over a period of 40 days. The lipids of those diets had a peroxide val ue of 5.1, 9.5, and 74 mEq O-2/kg, respectively, on average over the w hole feeding period. Additionally, according to a bifactorial design, the vitamin E supply of the animals was varied (11 versus 511 mg alpha -tocopherol equivalents per kg of diet). In order ro evaluate the effe cts of dietary fat and vitamin E supply on the vitamin E status, the t ocopherol concentrations in plasma, liver, kidney, heart and adipose t issue were measured. As expected, the vitamin E supply had a marked ef fect on the vitamin E status. In contrast, feeding the moderately oxid ized soybean oil did riot considerably affect the vitamin E status rel ative to feeding the fresh soybean oil. A slight drop in tocopherol co ncentrations was observed only in liver and plasma (at the low dietary vitamin E level) and in kidney (ar the high dietary vitamin E level) whereas the tocopherol concentrations in the heart and adipose tissue remained completely unchanged by feeding the oxidized soybean oil in c omparison to feeding the fresh soybean oil. The type of fatty acids in gested was a more important factor influencing the vitamin E status. I n this respect, rats fed the coconut oil at both dietary vitamin E lev els exhibited a slightly:ly higher vitamin E status than those rats fe d fresh or oxidized soybean oil. The fatty acid composition oi liver t otal lipids was only slightly influenced by feeding the oxidized oi, a nd that of the erythrocyte membrane total lipids remained completely u nchanged. by feeding the oxidized soybean oil in comparison with feedi ng the fresh,soybean oil. This suggests that the dietary oxidized oil did not influence the fatty acid metabolism. On the other hand, among the groups fed soybean oil, a low dietary vitamin E level reduced leve ls of PUFA relative to a high dietary vitamin E level. This suggests a loss of PUFA by lipid peroxidation in rats fed a low vitamin E diet a t a high intake of PUFA. Although feeding the oxidized soybean oil did not affect the fatty acid composition and the ratio between cholester ol and erythrocyte membranes, it increased the osmotic resistance agai nst hemolysis during incubation in hypotonic solutions, regardless of the dietary vitamin E level. In conclusion, the study shows that a mod erately oxidized oil has little effect on vitamin E status and fatty a cid metabolism; however, as shown bt; the model of the osmotic fragili ty of erythrocytes, membrane properties can be influenced even by mode rately oxidized oils.