Effects of microwave treatment on the oxidative stability of peanut (Arachis hypogaea) oils and the molecular species of their triacylglycerols

Peanut seeds (Arachis hypogaea) were roasted for 6, 12, 20, or 30 min at a frequency of 2450 MHz using a microwave oven. The quality characteristics and the compositions of the oils, i.e. their tocopherol distributions and the molecular species of the triacylglycerols (TAGs) were investigated. These results were compared with those of an unroasted oil sample. Only minor increases (p <0.05) in chemical and physical properties of the oils, such as the carbonyl value, the p-anisidine value and the color development occurred after a prolonged roasting period. Compared to the original level, more than 92 wt-% tocopherols remained after 30 min of roasting. A modified thin-layer chromatography argentation procedure provided 12 different groups of TAGs, based on both the degrees of unsaturation and the total fatty acid chain-length. Although significant increases (p <0.05) generated in these chemical and physical changes of the oils after 20 min of roasting, no significant loss (p >0.05) was observed in the molecular species of the TAGs during microwave roasting. These results indicate that phospholipids may be attributed to the quality characteristics of peanut oils during microwave roasting.