Bio-Heat Is a Key Environmental Driver Shaping the Microbial Community of Medium-Temperature Daqu

Abstract

"Daqu" is a saccharifying and fermenting agent commonly used in the traditional solid-state fermentation industry (e.g., baijiu and vinegar). The patterns of microbial community succession and flavor formation are highly similar among batches, yet the mechanisms promoting temporal succession in the Daqu microbial ecology remain unclear. Here, we first correlated temporal profiles of microbial community succession with environmental variables (temperature, moisture, and titratable acidity) in medium temperature Daqu (MT-Daqu) throughout fermentation. Temperature dynamics significantly correlated ( < 0.05) with the quick succession of MT-Daqu microbiota in the first 12 d of fermentation, while the community structure was relatively stable after 12 d. Then, we explored the effect of temperature on the MT-Daqu community assembly. In the first 4 d of fermentation, the rapid propagation of most bacterial taxa and several fungal taxa, including ,, and unclassified and species, significantly increased MT-Daqu temperature to 55°C. Subsequently, sustained bio-heat generated by microbial metabolism (53 to 56°C) within MT-Daqu inhibited the growth of most microbes from day 4 to day 12, while thermotolerant taxa, including , unclassified, ,, , and survived or kept on growing. Furthermore, temperature as a major driving force on the shaping of MT-Daqu microbiota was validated. Lowering the fermentation temperature by placing the MT-Daqu in a 37°C incubator resulted in decreased relative abundances of thermotolerant taxa, including ,, and , in the MT-Daqu microbiota. This study revealed that bio-heat functioned as a primary endogenous driver promoting the formation of functional MT-Daqu microbiota. Humans have mastered the Daqu preparation technique of cultivating functional microbiota on starchy grains over thousands of years, and it is well known that the metabolic activity of these microbes is key to the flavor production of Chinese baijiu. The pattern of microbial community succession and flavor formation remains highly similar between batches, yet mechanistic insight into these patterns and into microbial population fidelity to specific environmental conditions remains unclear. Our study revealed that bio-heat was generated within Daqu bricks in the first 4 d of fermentation, concomitant with rapid microbial propagation and metabolism. The sustained bio-heat may then function as a major endogenous driving force promoting the formation of the MT-Daqu microbiota from day 4 to day 12. The bio-heat-driven growth of thermotolerant microorganisms might contribute to the formation of flavor metabolites. This study provides useful information for the temperature-based modulation of microbiota function during the fermentation of Daqu.

Characterisation of physicochemical properties, flavour components and microbial community in Chinese Guojing roasted sesame-like flavourDaqu

“…Previous studies have found that Bacillus are derived from the tools used to make Daqu . Thermoactinomyces have been reported previously in RSF Daqu and may be derived from the raw materials in Daqu , and microbial exothermy also contributes to make it a dominant genus . Thermoactinomyces produce a rich enzyme system that includes esterase and phosphatase and is likely to be relevant to the formation of flavour compounds in RSF Baijiu .…”

“…During Baijiu fermentation microorganisms convert protein into amino acids and starch into glucose, and produce many flavour precursors and flavour components such as esters, pyrazines, aromatic and phenolic compounds. Metabolic heat was a primary endogenous driver to promote Bacillus , which are thermotolerant taxa and commonly found in Daqu . Previous studies have found that Bacillus are derived from the tools used to make Daqu .…”

High throughput sequencing of the bacterial composition and dynamic succession in Daqu for Chinese sesame flavour liquor

“…The brewing of liquor is a process in which microorganisms use raw materials to produce the metabolites that form flavour substances . There are differences in the microbial species and community structures of different flavour liquors, which is one of the factors affecting the formation of different liquor flavours .…”

“…During the fermentation process of Chinese Shaoxing rice wine, ten genera ‐ Bacillus , Leuconostoc , Lactococcus , Weissella , Thermoactinomyces , Pseudomonas , Saccharopolyspora , Staphylococcus , Enterobacter and Lactobacillus ‐ were identified as the main bacteria, with Bacillus and Lactobacillus dominant . Xiao et al reported that metabolic heat was a major driving force promoting the formation of microbiota in medium temperature (MT) Daqu from day 4 to 12. During this period, the heat generated by microbial metabolism (53 to 56°C) within MT Daqu inhibited the growth of most microbes, while thermotolerant taxa including Bacillus , unclassified Streptophyta , Weissella , Thermoactinomyces , Thermoascus , and Thermomyces , survived or continued to grow.…”

Lactic acid bacteria in the brewing of traditional Daqu liquor

“…Wang et al reported finding Lactobacillus , Leuconostoc , Weissella , Lactococcus , and Pediococcus in medium temperature Daqu, when investigating the main source of prokaryotic microorganisms in fermented grains of medium temperature Daqu liquor. Xiao et al explored the effects of temperature on the microbial community of medium temperature Daqu. They isolated Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Weissella , and observed that in the initial fermentation stage (up to day 4), other bacteria could grow rapidly in addition to bacteria such as Leuconostoc .…”