Community-level bioaugmentation results in enzymatic activity- and aroma-enhanced Daqu through altering microbial community structure and metabolic function

Using the previous batch of fermented product to initiate fermentation (i.e., community-level bioaugmentation) is a common production technique for fermented foods. As the saccharification, fermentation, and aromaproducing agent in strong-flavor Baijiu brewing, medium-temperature Daqu is usually produced by spontaneous fermentation without any exogenous microorganisms inoculated. Here, we selected Daqu from day 12 (FerDq) and day 30 (MatDq) of the previous batch as starters to perform bioaugmentation. Bioaugmentation enhanced total acidity, enzymatic activities, and volatiles, particularly alcohols and pyrazines. Metagenomics revealed that bioaugmentation with 5% or 10% (w/w) FerDq enhanced the relative abundances of Staphylococcus and Bacillus, whereas bioaugmentation with 5% or 10% (w/w) MatDq enriched Bacillus, Aspergillus, Talaromyces, and Rasamsonia. The increase in liquefying activity in MatDq groups was due to the increase in alpha-amylase and glycogen phosphorylase abundances, mainly caused by the enrichment of Aspergillus, Talaromyces, and Bacillus. Bioaugmentation with FerDq significantly increased the gene abundance of carboxyesterase and esterifying activity of Daqu via Staphylococcus and Bacillus. The enriched Bacillus, Staphylococcus, and Paenibacillus in FerDq groups facilitated the production of pyrazines. The metabolic pathway of phenylethyl alcohol biosynthesis varied among different groups. In the control group, it was mainly produced by aryl-alcohol dehydrogenase, which originated from Lactobacillales, while in the bioaugmented groups, it was mainly produced through alcohol dehydrogenase and formaldehyde dehydrogenase, which were derived from Rhizopus and Bacillus in the FerDq groups and from Rasamsonia, Talaromyces, Rhizopus, and Bacillus in the MatDq groups. This study revealed the feasibility of producing enzymatic activity- and aroma-enhanced Daqu through communitylevel bioaugmentation.