Classification of fermented soybean paste during fermentation by ¹H nuclear magnetic resonance spectroscopy and principal component analysis

Fermented soybean paste (doenjang, FSP) is a traditionally fermented Korean food produced by fermentation with various microorganisms that is known to exhibit various beneficial bioactivities. To investigate the changes in nonvolatile metabolites of FSP during fermentation, samples produced with six fermentation times were analyzed using an ¹H nuclear magnetic resonance spectroscopy (NMR)-based metabolomics technique. This revealed clear separation of 50% methanol extracts of the FSP samples with different fermentation times in the principal component plots by combining PC1 and PC2, which cumulatively accounted for 94.2% of the variance. Major compounds contributing to the separation of 50% methanol extracts of FSP with various fermentation times were isoleucine/ leucine, lactate, alanine, acetic acid, glutamine, choline, tyrosine, and phenylalanine. In addition, the 1H NMR spectra of chloroform extracts were separated mainly by a combination of PC1 and PC3, which accounted for 72.6% of the variance. The present study suggests the usefulness of a ¹H NMR-based metabolomics approach to discriminate FSP samples subjected to different fermentation times, and this is the first report regarding metabolomic profiling of FSP.