Effects of microwave heating were investigated on chemical properties of seed oils in relation to tocopherol contents. For assessing quality of oils (linseed, soybean, corn, olive, and palm) during microwave treatments, peroxide, thiobarbituric acid, carbonyl and anisidine values were determined. As the amount of polyunsaturated fatty acids in oils increased the index for the chemical properties increased. After 8-10 min heating the amount of tocopherols decreased substantially in linseed, olive and palm oils, whereas that in corn and soybean oils was still ca. 90%. Thus, the reduction in tocopherols in oils is not necessarily in agreement with chemical properties of the oils.
The relative stabilities of individual tocopherols during microwave heating were investigated in fatty acid esters and tocopherol-stripped vegetable oils. The rate of tocopherol loss during heating was less from the highly unsaturated ethyl esters or vegetable oils than from ethyl laurate or olive oil. However, changes in chemical properties of the substrates depended on degree of unsaturation of esters and oils. The stability of tocopherols during microwave heating was 6 > p > y > > o, and the order did not change with differences in the type of ethyl esters of fatty acids or oils.
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