Microwave roasting and phospholipids in soybeans (Glycine max L) at different moisture contents

The effects of microwave roasting on phospholipids in soybeans were investigated in relation to moisture. Whole soybeans at different moistures (9.6, 38.2, and 51.9%) were roasted by exposure to microwaves at a frequency of 2,450 MHz. During microwave treatments, the lower the moisture content, the higher was the internal temperature in soybeans at the end of microwave roasting. Total lipids were extracted from the beans after microwave treatment, and the phospholipids were separated with thin-layer chromatography. Phosphatidylcholine was the principal phospholipid in the extracted lipids from all unroasted and roasted bean samples. After microwave roasting, phospholipids containing an amino group, especially phosphatidylethanolamine, decreased substantially (P < 0.05) in lower-moisture soybeans. However, increasing the moisture content depressed a rise in the internal temperature of soybeans and prevented a reduction in phospholipids and/or polyunsaturated fatty acids in the phospholipids. Based on the changes in the composition and fatty acid distribution of phospholipids in soybeans during microwave roasting, it is necessary to consider the moisture content in soybeans when roasting in a microwave oven.