Physicochemical Factors Affecting Microbiota Dynamics During Traditional Solid-State Fermentation of Chinese Strong-Flavor Baijiu

Abstract

Spontaneous solid-state fermentation (SSF) of Chinese Baijiu involves diverse microbes from Daqu and pit mud (PM). Given that the transfer of interphase microflora during the fermentation is a continuous and dynamic process, longitudinal studies are essential to provide ecological insights into community stability and response to consecutive disturbances in the process. In this context, this study aimed to generate a comprehensive longitudinal characterization of the microbiota during the fermentation processes of Chinese strong-flavor Baijiu (CSFB) differing in cellar ages with consideration for potential relation to physicochemical variables. The microecology variations observed during the 6-years cellar SSF (SCSSF) and 30-years cellar SSF (TCSSF) processes reveal that fungal composition contributes to a larger extent than bacterial composition to such variations. Orders of Lactobacillales, Anaerolineales, Enterobacteriales, Bacillales, Eurotiales, and Saccharomycetales dominated (average relative abundances >10%) the microbiota in both SCSSF and TCSSF processes but with a different percentage in the operational taxonomic unit (out) abundances. Compared with the SCSSF process, TCSSF possessed slower microbial succession rates, which were in accordance with the profile of physicochemical properties. From a network perspective, the microbial community structure observed in the TCSSF processes was more stable than that in the SCSSF. This may benefit from the milder physicochemical conditions of the TCSSF processes, especially the temperature, which is also more beneficial to the growth of some groups that have negative effects on fermentation, such as Staphylococcus, Pseudomonas, and Acinetobacter.

Characteristics of the Microbial Community in the Production of Chinese Rice-Flavor Baijiu and Comparisons With the Microflora of Other Flavors of Baijiu

“…At the late stage of fermentation, the anaerobic environment is dominant, the nutrient content decreases, and the acidity and alcoholic content increases, which inhibit the growth of some microorganisms and lead to a decrease in species diversity. The changing pattern of microbial diversity is consistent with that in the brewing of strong- ( Tan et al, 2019 ; Guan et al, 2020 ), mixed- ( Liu and Miao, 2020 ), and light-flavor baijiu ( Dong et al, 2020 ).…”

“…Generally, Rhizopus plays major roles in the saccharification stage, and gradually decline in the fermentation stage due to the decrease in oxygen content, while the abundance of other acid-tolerant and alcoholic anaerobic fungi, such as yeast, gradually increases ( Wu H. et al, 2017 ; Yin et al, 2020a ). However, in this study, Rhizopus maintained high abundance from the beginning to the end of fermentation, which was very different to the microorganisms in the brewing of light- and strong-flavor baijiu ( Guan et al, 2020 ; Hu et al, 2021b ). The main fungi in light-flavor baijiu brewing are Saccharomyces , Aspergillus , Rhizopus , Pichia , Candida , and Wickerhamomyces ( Hu et al, 2021b ).…”

“…The main bacterial genera in the Xiaoqu light-flavor baijiu were Lactobacillus , Acetobacter , Weissella , Lactococcus , and Bacillus ( Dong et al, 2020 ; Hu et al, 2021a , b ). In strong-flavor baijiu, the main bacteria genera were Kosakonia , Lactobacillus , Weissella , Pediococcus , Pantoea , and Bacillus , which accounted for more than 86% of the bacterial abundance ( Guan et al, 2020 ).…”

“…In addition, Rhizopus produces glucoamylase and proteases as well as important flavor substances, such as lactic acid, other organic acids, and aromatic series. Yeasts can produce aldehyde esters, β-phenylethanol, and other higher alcohols during fermentation, and form flavor substances with ethyl acetate as the main ester ( Guan et al, 2020 ). Among the many microbial groups, only the core microorganisms can drive the fermentation process, and they not only produce various flavor substances, but more importantly, they can maintain the interactions among microorganisms, which together determine the quality of baijiu ( Song et al, 2017 ).…”

“…It is currently unclear whether there are differences in the composition of the microbial communities in the production of these two flavor types of baijiu. In addition, there have been more studies of the brewing microorganisms of light- ( Dong et al, 2020 ; Hu et al, 2021b ), strong- ( Guan et al, 2020 ), and sauce-flavor baijiu ( Dai et al, 2020 ), but less of rice-flavor baijiu, and its brewing microbial composition has yet to be resolved. Therefore, in this study, high-throughput sequencing technology was used to analyze the microbial communities in the starters and production processes of rice-flavor baijiu to identify the core microbiota and study their effects on the microbial communities by combining with changes in physicochemical factors, such as flavor components.…”