Exploring the regulated effects of solid-state fortified Jiuqu and liquid-state fortified agent on Chinese Baijiu brewing.

Zaopei is the direct source of Chinese liquor (Baijiu). Adding functional strains to Zaopei is a potential strategy to regulate Baijiu brewing, mainly including the two ways of solid-state fortified Jiuqu (SFJ) and liquid-state fortified agent (LFA). Here, to explore their regulated details, the response patterns of Zaopei microecosystem and the changes in the product features were comprehensively investigated. The results showed that SFJ more positively changed the physicochemical properties of Zaopei and improved its ester content, from 978.57 mg/kg to 1078.63 mg/kg over the fermentation of 30 days, while LFA decreased the content of esters, alcohols, and acids. Microbial analysis revealed that SFJ significantly increased Saccharomycopsis and Aspergillus from the start of fermentation and induced a positive interaction cluster driven by the added functional Paenibacillus, while LFA exhibited a community structure near that of the original microecosystem and led to a simpler network with the reduced microbial nodes and correlations. Metabolism analysis found that both SFJ and LFA weakened the flavor-producing metabolism by suppressing some key enzyme pathways, such as EC 3.2.1.51, EC 4.2.1.47, EC 1.1.1.27, EC 1.1.1.22, EC 1.5.1.10, EC 1.14.11.12. As a result, SFJ improved the raw liquor yield by 28.5 % and endowed the final product with a more fragrant aroma, mainly through ethyl (E)-cinnamate, ethyl isovalerate, ethyl phenacetate with the higher odor activity values, while LFA promoted the yield by 13.2 % and resulted in a purer and less intense aroma through the aroma-active ß-damascenone, ethyl heptoate, ethyl phenacetate. These results facilitated the regulated mechanism of SFJ and LFA on Baijiu brewing and indicated that the used functional strains in this study could be applicated in SFJ way for the further industrial-scale application.

The active synergetic microbiota with Aspergillus as the core dominates the metabolic network of ester synthesis in medium-high temperature Daqu.

The active ester-synthesis microorganisms in medium-high temperature Daqu (MHT-Daqu) largely impact the strong-flavor Baijiu quality, while their actual composition and metabolic mechanism remain unclear. Here, to explore how the active microbiota contributes to MHT-Daqu ester biosynthesis, metatranscriptomic and metaproteomic analyses coupled with experimental verification were performed. The results showed that the MHT-Daqu microbiota with the higher ester-forming ability exhibited a more active dynamic alteration from transcription to translation. The genera Aspergillus, Bacillus, Leuconostoc, and Pediococcus could transcribe and translate obviously more ester-forming enzymes. In the ester-synthesis metabolic network, the synergetic microbiota confirmed by interaction analysis, containing Eurotiales, Bacillales, and Saccharomycetales, played an essential role, in which the Eurotiales and its representative genus Aspergillus contributed the highest transcript and protein abundance in almost every metabolic process, respectively. The recombined fermentation verified that their corresponding genera could produce the ester and precursor profiles very close to that of the original MHT-Daqu active microbiota, while the microbiota without Aspergillus caused a polar separation. These results indicated that the synergetic microbiota with Aspergillus as the core dominated the metabolic network of ester synthesis in MHT-Daqu. Our study provides a detailed framework of the association between the active synergetic microbiota and ester synthesis in MHT-Daqu.

Contrasting the microbial community and non-volatile metabolites involved in ester synthesis between Qing-flavor Daqu and Nong-flavor Daqu.

Daqu, a fermentation starter, was important source of key flavors of Chinese Baijiu. The quality of Chinese Baijiu could be significantly affected by the ester-synthesis microorganisms. In order to clarify the microbial community that promoted the ester formation in Daqu, the dynamic changes of microbial community and non-volatile profiles of Qing-flavor Daqu and Nong-flavor Daqu samples through the whole making process were investigated by Illumina MiSeq platform and liquid chromatograph-mass spectrometry (LC-MS). The non-volatile compounds related to ester synthesis were identified by comparing with ester synthesis pathway and partial least squares discriminant analysis (PLS-DA). Correlations between microbial community and non-volatile metabolites involved in ester synthesis of two types of Daqu were disclosed by Pearson correlation analysis. Results showed that a total of 50 key compounds involved in ester synthesis were identified and 25 primary functional microorganisms were screened in 39 samples. Among them, in Qing-flavor Daqu, the top three primary functional microorganisms that had strong correlations with ester-formation precursors were Lactobacillus, Pantoea, and Sphingomonas; Lactobacillus and Pantoea had significantly positive interactions with various microorganisms, but Sphingomonas did not interact with others. In Nong-flavor Daqu, the top three primary functional microorganisms that had strong correlations with ester-formation precursors were Candida, Apiotrichum, and Cutaneotrichosporon. Candida showed strong positive correlation with other microorganisms, whereas Apiotrichum and Cutaneotrichosporon had no interaction with other microorganisms. The study could help our understanding of the microbial metabolism process in Daqu and provided a scientific basis for a controllable and feasible fermentation system.