Abstract:

The fatty acids of traditional soybean paste were extracted by Soxhlet extraction and esterified with acid and/or
alkaline, and then the esterified products were analyzed by gas chromatography-mass spectrometry (GC-MS) after extraction
with n-hexane, identified by spectral searching using the NIST11.L mass spectral library combined with organic mass
spectral data and quantified by peak area normalization. Results showed that complete separation of the fatty acid methyl
esters was achieved in 33 minutes after derivatization. Ten kinds of fatty acids were identified by acid esterification, among
which the predominant fatty acids were n-hexadecanoic acid methyl ester (13.62%), oleic acid methyl ester (23.95%) and
linoleic acid methyl ester (48.91%). Four kinds of fatty acids were identified by alkaline esterification, among which the
predominant fatty acids were oleic acid methyl ester (10.42%) and linoleic acid methyl ester (19.63%). Ten kinds of fatty
acids were identified by acid-alkaline esterification, among which the predominant fatty acids were n-hexadecanoic acid
methyl ester (13.64%), oleic acid methyl ester (24.16%) and linoleic acid methyl ester (49.07%). To conclude, the acidalkaline
esterification method allows rapid, accurate and reliable identification of fatty acids in traditional soybean paste
without using reference standards.

Key words: traditional soybean paste, fatty acid, methylation, gas chromatography-mass spectrometry (GC-MS)