GC × GC-TOF/MS and UPLC-Q-TOF/MS based untargeted metabolomics coupled with physicochemical properties to reveal the characteristics of different type daqus for making soy sauce aroma and flavor type baijiu

Daqu is the starter for making baijiu (Chinese liquor). Daqu impart distinctive flavors to baijiu, but understanding of the metabolite composition and factors affecting fermentation performance of yellow, white and black daqu are limited. In this study, the relationship between the physicochemical properties of daqu and their metabolic profiles was determined. A total of 647 compounds were identified in daqu, including 401 volatile compounds, mainly aromatic compounds and pyrazines, and 246 non-volatile compounds which were mainly organic and amino acids. Correlation analysis showed that liquefying power, saccharifying power and pH were the main physicochemical properties accounted for the differences in metabolic profile between the three types of daqus. A group of 48 biomarkers (mainly alcohols, aromatics and non-volatile organic acids) selected by multivariate statistical analysis, could clearly distinguish between different types of daqu. Different metabolite phenotypes in three types of daqu were mainly caused by 21 metabolic pathways.