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.