Fatty acid distributions of triacylglycerols and phospholipids in peanut seeds (Arachis hypogaea L.) following microwave treatment

Peanut seeds (Arachis hypogaea L.) were roasted for 6, 12, 20 or 30 min at a frequency of 2450 MHz using a microwave oven. The fatty acid distributions of triacylglycerols (TAGs) and phospholipids (PLs) isolated from total lipids in these seeds was investigated. The predominant lipid component was TAGs and the lesser one PLs, while steryl esters, free fatty acids (FFAs), and sn-1,3- and sn-1,2-diacylglycerols (DAGs) were minor ones. Following microwave roasting, a significant increase (P<0.05) was observed in FFAs and in both forms of DAGs. The greatest PL losses (P<0.05) were observed in phosphatidyl ethanolamine, followed by phosphatidyl choline and phosphatidyl inositol. However, the principal characteristics of fatty acid distributions in the TAGs were evident after 20 min of roasting: unsaturated fatty acids, especially linoleic and/or oleic, were predominantly concentrated in the sn-2-position, and saturated fatty acids, especially stearic and/or palmitic, primarily occupied the sn-1-position or sn-3-position of peanut oils during microwave roasting. These results indicate that unsaturated fatty acids located in the sn-2-position are significantly protected from oxidation during microwave roasting.