Abstract
Wheat-originated microbes play an important role in shaping the quality of high-temperature Daqu which is commonly used as a starter for producing sauce-flavor Baijiu. However, the shifts of microbiota from raw material to fresh Daqu and then to mature Daqu remain unclear. Hence, in the present study, the inner and outer of fresh and mature Daqu were collected to explore the correlation between microbiota and metabolites as well as the source of the microbiota in Daqu. Results indicated that the activities of amylase and protease between the inner and outer of fresh Daqu varied significantly while both parts became similar after maturation. The predominant bacteria shifted from Saccharopolyspora (outer) and Staphylococcus (inner) to Kroppenstedtia (both outer and inner), while the predominant fungi shifted from Thermoascus (both outer and inner) to Byssochlamys (outer) and Fusarium (inner). A combining analysis of headspace solid-phase micro extraction-gas chromatography-mass spectrometry, headspace gas chromatography-ion mobility spectrometry, and nuclear magnetic resonance was employed to detect the metabolites. The network analysis was conducted to perform the relationships between microbes and metabolites. The results showed that the bacteria, especially Saccharopolyspora, Bacillus, and Acinetobacter, had a strong correlation with the productions of esters, amino acids and their derivatives, and sugars and their derivatives, while most fungi such as Thermoascus, were negatively correlated with the phenylalanine, trimethylamine n-oxide, and isovalerate. SourceTracker analysis indicated that wheat was the important source of the Daqu microbiota, especially, the microorganisms in the inner of Daqu might be the drivers of the microbial succession during maturation. This study provided a comprehensive exploration to understand the microbial sources and shifts in high-temperature Daqu during maturation.
Highlights
Baijiu is a fermented alcoholic beverage and plays an important role in the history of Chinese food culture for 3000 years (Jin et al, 2017)
Wheat-originated microbes were an important source for the microbial community formation of Daqu, especially the inner of Daqu
The difference in the bacterial community between the inner and outer of Daqu decreased and the predominant microbes shifted from Saccharopolyspora and Staphylococcus of fresh Daqu to Kroppenstedtia of mature Daqu, in which was indicated by the difference in metabolites
Summary
Baijiu is a fermented alcoholic beverage and plays an important role in the history of Chinese food culture for 3000 years (Jin et al, 2017). The popularity of Baijiu to a great extent is due to its rich tastes and characterized flavors, both of which are produced in the complex production processes, including solid-state fermentation, distillation, storage, and blending (Xu et al, 2010). Fermentation plays an important role in the production of volatile flavors and critical secondary metabolites (Zheng et al, 2011). Daqu production needs a series of steps, including moistening, breaking, mixing shaping, spreading, incubating, and maturation (Zheng et al, 2011). Maturation is the vital step that involves microbial enrichment, primary and secondary metabolic processes, and changes in diverse microbes and metabolites (Fan et al, 2019)
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