Comparative Degradation Effects of Sesame and Soybean Oil during Heating using Microwave Irradiation

Changes of quality parameters upon heating were evaluated at different times of microwave heating on refined sesame and soybean oil high and compared to the results obtained for standard chemical indices (free fatty acids, peroxide, p-anisidine, nonenal content). Soybean oil was more extensively oxidised by microwave heating than the other oil probably as a consequence of absence of natural antioxidants. Microwave heating also induced alterations in heating profiles of the oils [Acid value of (0.67±0.04) and (1.8±0.01); peroxide value of (1.86±0.09) and (37.83±0.23); p-anisidine value of (16.46±0.12) and (18.23±0.23) after 10 minutes at high power for sesame and soybean oils respectively]. Presence of frying components in soybean oil like polyunsaturated fatty acids (almost 58%) enhanced thermo-oxidation and resulted in its poor stability. The analysis of heating profiles and related thermal properties like response to nonenal appeared to be a valuable tool to assess different degrees of lipid oxidation induced by microwave heating in vegetable oils. Nonenal content of (13.08±0.02) µmol/gm for sesame oil and (17.28±0.08) µmol/gm for soybean oil at high power showed their comparative thermal stability.