Primary and secondary metabolite profiling of doenjang, a fermented soybean paste during industrial processing

In this study, a comprehensive metabolite profile analysis of doenjang, a fermented soybean paste, at various steps of its industrial 5-step production process was conducted, by combining gas and liquid chromatography-mass spectrometry techniques with multivariate analysis. From the partial least squares discriminant analysis of primary and secondary metabolites, the patterns were clearly distinguishable between the various processing steps (step 1: steaming, step 2: drying, step 3: meju fermentation, step 4: brining, step 5: doenjang aging). Of the primary metabolites, most of the monosaccharides, amino acids, and fatty acids increased in steps 3-5. Isoflavone and soyasaponin derivatives were major secondary metabolites identified during the processing of doenjang. Isoflavone glycosides gradually decreased after step 1, while isoflavone aglycones distinctly increased in steps 4-5. Soyasaponins generally decreased during processing after step 2. Increased isoflavone aglycones, such as daidzein, glycitein, and genistein, were observed in steps 4-5 showed the strongest positive correlation with doenjang's antioxidant potential and total phenolic content.