Variations in the composition of various acyl lipids, tocopherols and lignans in sesame seed oils roasted in a microwave oven

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Seeds from various strains of cultivated Sesamum indicum Linn (colour of seeds: black, brown and white) were exposed to microwave roasting for 16 and 30min at a frequency of 2450 MHz and were studied not only for different acyl lipids and their fatty acid compositions, but also for the contribution of anti‐oxidants to the oxidative stability of the oils. Lipids from all‐seeded strains were comparable in their total fatty acid composition, with linoleic, oleic, stearic and palmitic acids as the major acids. The total lipids were isolated by thin‐layer chromatography into the following five fractions: triacylglycerols (TAG), diacylglycerols, free fatty acids, polar lipids and steryl esters. The TAG were slightly and randomly hydrolysed by microwaves, but was still representing 900 g kg−1 of the total lipids at 30min of roasting. Although burning and bitter tastes occurred at the time, the tocopherols and lignans still amounted to over 80% of the original level. The results suggested that the oxidative stability of the oils would probably be due to the synergism between endogenous antioxidants and browning substances produced during microwave roasting.