Corresponding FAMEs of the oil samples and the lipids extracted
from fat samples were prepared by esterification with potassium
hydroxide following the AOCS Official Method Ce 2-66 (AOCS,1997)
with minor modification. Approximately 10 mg of sample was dissolved in 2 mL of n-heptane in a tube with tight sealing cap, and
0.1 mL of methanolic potassium hydroxide solution (2 mol/L) was
added. The tube was capped tightly and shaken vigorously for
about 30 s. The solution was then centrifuged at 3000 g for 5 min,
and 1 mL of n-hexane upper phase was transferred into 2 mL autosampler
vial for subsequent GC analysis. Monoheneicosanoin
methyl ester (C21:0, 5 mg/mL)was used as the internal standard for
the GC analysis