Preparation of FAME
After the heating process, the sample oil was methylated using a KOH−methanol solution based on the AOCS official Method Ce 2-66 with a slight modification [10]. In detail, 10 mg of each oil sample was transferred into a stoppered glass tube with 10 μL of C21:0TAG (5 mg/mL) as an internal standard. Then 2 mL of n-heptane was added to dissolve the sample, followed by addition of 1.0 mL of 0.5 mol/L KOH−methanol. The tube was closed and shaken vigorously for 2 min. After 30 min, the upper layer was transferred to a test tube, followed by addition of a small amount of anhydrous sodium sulfate to remove excessive moisture, and then the dry heptane solution was transferred to a 1.5-mL glass vial for the following analysis.