Fatty Acid Composition
The fatty acids profile of soybean oil was determined by converting fatty acids into their methyl esters (FAMEs). In brief, 0.3 g of oil samples were added to 7 mL of hexane and then methylated with 2 mL of methanolic potassium hydroxide solution (7 N) for 10 min at 50 °C. The gas-liquid chromatography (GC, HP-5890, Hewlett-Packard, CA, USA) equipped with a flame ionization detector (FID) was employed to identify FAMEs. The capillary column used was CP-FIL 88 (Suppl Co., Inc., Bellefonte, PA, USA). The flow rate of carrier gas (nitrogen) was 0.75 mL/min. The temperature of both injector and detector was kept at 250 °C, and that of the oven at 198 °C. The composition of fatty acids was calculated in relative area percentages (Fatemi and Hammond, 1980).