Constructing simplified microbial consortia to improve the key flavour compounds during strong aroma-type Baijiu fermentation

The ester compounds play key roles in maintaining the sensory characteristics of alcoholic beverages. For strong aroma-type Baijiu fermentation, the volatile acids from pit mud microbes are key precursors for ester synthesis. However, the volatile acids can only be efficiently synthesized by the pit mud microbes in grains which attaches to pit mud. Elevating the ester contents in the upper layer's fermented grains is vital to improve the quality of raw liquor. In this study, we applied top-down strategy and aim to simplify and obtain pit mud microbial consortia to efficiently produce caproate but not off-flavour compounds. The simplified consortia with Caproiciproducens spp. as dominant species can use unsterilized fermentation water as sole substrate for caproate production, and stable caproate production was achieved by inoculating these simplified consortia in scaling-up fermentation. The fermented broth was then applied to facilitate the fermentation of upper layer's grains to prompt ester synthesis. Finally, the contents of variety esters such as ethyl caproate, ethyl pentanoate and ethyl octanoate were markedly increased. Together, this study demonstrates that constructing simplified microbial consortia containing key flavour-producing species is feasible to improve the flavour quality of spontaneously fermented foods.