Metabolomics reveals the effect of garlic on antioxidant- and protease-activities during Cheonggukjang (fermented soybean paste) fermentation

•Garlic caused different metabolic states during Cheonggukjang fermentation.•Garlic added Cheonggukjang showed higher antioxidant activity than Cheonggukjang.•Inhibited protease activity by garlic was related to decreased amino acids content.

We performed mass spectrometry (MS)-based metabolite profiling of Cheonggukjang (CGJ) and three types of garlic (normal, sprouted, and fermented) added CGJ (G-CGJ). Metabolite profiling suggested that the major distinguishing factor between the four types of CGJ lay in whether garlic was added, although different metabolic states were observed in G-CGJ. Among the discriminant metabolites between CGJ and G-CGJ, the levels of four amino acids such as l-valine, l-isoleucine, l-leucine, and glycine were decreased in G-CGJ compared to CGJ because garlic inhibited the protease activity of Bacillus subtilis during fermentation. In addition, the relative contents of l-cysteine, s-allyl-cysteine, s-allyl-cysteine sulfoxide, soyasaponin βg, and soyasaponin γg, which showed positive correlation with antioxidant activities, were high in G-CGJ. These results suggest that MS-based metabolite profiling could be a useful tool for understanding the metabolic differences of fermented foods according to the additives, and their relationship with antioxidant activity.