Changes in microbial community during fermentation of high-temperature Daqu used in the production of Chinese 'Baiyunbian' liquor

Daqu is a fermentation starter used in the production of Chinese liquor. The present study investigated changes in the microbial community during the fermentation of Baiyunbian high-temperature Daqu during a cycle time of 140 days. Two methods were used, a culture-dependent method (viable cell counting) and a culture-independent method (high-throughput sequencing of bacterial 16S rRNA gene and fungal internal transcribed spacer region). It was found that thermotolerant microorganisms such as Bacillus, Thermomyces and Actinobacteria were dominant in all stages of Daqu fermentation, especially during the high-temperature period of days 7-38. In the initial 110 days of fermentation, operational taxonomic units and number of bacteria were higher than those of fungi, but the opposite was observed towards the end of fermentation (day 140). In mature Daqu, the predominant bacterial species were Bacillus and unclassified Thermoactinomycetaceae, followed by Thermoactinomyces, Kroppenstedtia and Saccharopolyspora; the predominant fungi were Aspergillus, unclassified Trichocomaceae, Thermomyces, Rhizopus, Monascus and Candida, among others. It is possible that the addition of mother Daqu, temperature and storage time played critical roles in the microbial composition of Daqu. Collectively, the above findings provide important information that can be used to optimize conditions for largescale production of Daqu. Copyright (C) 2017 The Institute of Brewing & Distilling