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.