Microbial interactions could impact the metabolic behavior of microbes involved in food fermentation, and therefore they are important for improving food quality. This study investigated the effect of Bacillus licheniformis, the dominant bacteria in the fermentation process of Chinese Maotai-flavor liquor, on the metabolic activity of Saccharomyces cerevisiae. Results indicated that S. cerevisiae inhibited the growth of B. licheniformis in all mixed culture systems and final viable cell count was lower than 20 cfu/mL. Although growth of S. cerevisiae was barely influenced by B. licheniformis, its metabolism was changed as initial inoculation ratio varied. The maximum ethanol productions were observed in S. cerevisiae and B. licheniformis at 10(6):10(7) and 10(6):10(8) ratios and have increased by 16.8 % compared with single culture of S. cerevisiae. According to flavor compounds, the culture ratio 10(6):10(6) showed the highest level of total concentrations of all different kinds of flavor compounds. Correlation analyses showed that 12 flavor compounds, including 4 fatty acids and their 2 corresponding esters, 1 terpene, and 5 aromatic compounds, that could only be produced by S. cerevisiae were significantly correlated with the initial inoculation amount of B. licheniformis. These metabolic changes in S. cerevisiae were not only a benefit for liquor aroma, but may also be related to its inhibition effect in mixed culture. This study could help to reveal the microbial interactions in Chinese liquor fermentation and provide guidance for optimal arrangement of mixed culture fermentation systems.

As one of the three major distilled spirits in the world, traditional Chinese liquor has a distinctive aroma and taste. The brewing process typically involves two stages: the Daqu-making process and the liquor-making process. Further, it commonly adopts solid state fermentation in an open environment, which involves diverse microorganisms such as bacteria and fungi. Yeasts, as an integral brewing microorganism, are not only a dominant force in the fermentation process but also play a key role in the quality and character of different flavour liquors. Studies on yeasts associated with Chinese liquor have rarely compared them with those associated with other alcoholic beverages (wine, sake, etc.), especially in the microbiomerelated flavour of the alcoholic beverage. Here, we review the Chinese liquor brewing process, the yeast community in the brewing process, the yeast derived flavour compounds, the interaction between yeasts and other microorganisms and gene level modifications.

Microbes are the major producers of alcohol and aromatic compounds in alcohol beverages. It is believed that, in addition to production techniques and grains, different micro-ingredient compositions yield variations in aromas and tastes. The bacterial communities of the three key phases from Moutai liquor production were profiled with the Illumina sequencing platform. A total of 54 bacterial families were detected and the microbial structure showed clear differences among samples. In the starter-making phase, Leuconostocaceae and Enterococcaceae dominated the shaping stage, and Bacillaceae dominated the mature starter and ripening stages. In the latter two phases, Bacillaceae and Lactobacillales dominated in the early stage of stack fermentation and the anaerobic stage of pit fermentation, respectively. Most of the important microbes (approximately 26 families) might have originated from the starter and greatly affected the bacterial structure of the samples during the early stages of stack fermentation. Production techniques and environmental factors, such as temperature and oxygen, also shaped the unique bacterial composition during different phases.