Comparative analysis of microbial community structure in the peel and core of Houhuo low-temperature Daqu

Abstract

The varying degrees of browning due to the Maillard reaction result in distinct characteristics across different parts within the cross-section of Houhuo low-temperature Daqu (LTD). However, the microbial community structure of the peel and core of Daqu is still poorly understood. In this study, using a combination of high-throughput sequencing and pure culture techniques, the microbial communities present in the peel and core of Houhuo LTD were compared and analyzed. Bacillus (58.84%) and Saccharomycopsis (87.61%) were the main bacterial and fungal genera present in Houhuo LTD. The abundance and diversity of fungi were significantly lower in peel samples (P < 0.01). At the bacterial genus level, Sphingobium, Staphylococcus, and Streptomyces were significantly enriched in peel samples, while Saccharopolyspora was significantly enriched in core samples (P < 0.05). At the fungal genus level, Saccharomycopsis and Clavispora were significantly enriched in peel samples, while Monascus and Aspergillus were significantly enriched in core samples (P < 0.05). Differences in the layers of LTD block had a greater effect on the correlation between bacterial genera, and the microbial networks in the peel samples were more compact. Some microbial groups were common to the two groups, including the main bacterial genera Bacillus, Saccharopolyspora, Streptomyces, and Staphylococcus and the main fungal genera Saccharomycopsis and Monascus. Pure culture techniques revealed that B. paralicheniformis, Pediococcus pentosaceus, and S. fibuligera were the most abundant strains of Bacillus, lactic acid bacteria, and yeast in all samples, respectively. The findings could support the optimization of the Daqu-making processes and the screening of microbial strains for brewing.