An integrated untargeted metabolomic approach reveals the quality characteristics of black soybeans from different geographical origins in China

Black soybeans are extensively planted and consumed in China due to their high nutritional value and numerous health benefits. However, very few is known about the characteristic metabolites of black soybeans from different geographical origins in China. In the present study, 31 black soybean samples were collected from 11 main producing provinces in China. A combined metabolomics approach using ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) and gas chromatography coupled to an Orbitrap mass analyzer (GC-orbitrap-MS) was performed for the first time to comprehensively investigate the metabolite variability among the black soybeans from different geographical origins. A total of 48 differential non-volatile metabolites and 14 differential volatile metabolites were identified based on orthogonal partial least squares discriminant analysis (OPLS-DA) coupled with analysis of variance (ANOVA). Higher procyanidin B1, procyanidin B2, epicatechin, malonylated isoflavones, and β-pinene were observed in Gansu black soybeans. Guangxi black soybeans had higher amounts of linoleic acid and its oxidation products of hexanal and pentane. The black soybeans from Xinjiang and Yunnan were found to have higher delphinidin-derived anthocyanins, gamma-glutamyl peptides, and aromatic hydrocarbons. The characteristic metabolites of black soybeans from other geographical origins were also clarified. This study indicated that the integrated untargeted metabolomic approach can be a powerful tool to provide knowledge for developing specialty black soybeans.