The microbial communities in Zaopeis, free amino acids in raw liquor, and their correlations for Wuliangye-flavor raw liquor production

Wuliangye-flavor liquor (WLFL), a specific Chinese traditional liquor, one of the major type of global distilled spirits, offers a unique flavor system acquired across thousands of years of development. Free amino acids (FAAs), as major health factors, are considered to be primarily derive from the hydrolysis of protein from the Zaopeis (ZPs) by microbial populations during fermentation. Here, we investigated the changes of microbial communities in ZPs and FAAs in raw liquor (RL) directly related ZPs from different ages of WLFL fermentation pits by phospholipid fatty acid fingerprint (PLFA) and high performance liquid chromatography method. Results indicated that the total PLFAs of 20- and 50-year ZPs were significantly higher (p < .05) than 1- and 5-year ZPs. Gram-positive bacteria (G+), anaerobic bacteria, and fungi were dominant in the ZPs. Furthermore, the total of FAAs content was highly increased (p < .05) in RLs of aged fermentation pit (20- and 50-year, 24.86-30.23 mg/g, 28.73-37.15 mg/g) compared with young (1- and 5-year, 20.97-26.46 mg/g, 17.83-28.70 mg/g), while, the different ages of RLs could be distinguished according to 9 biomarkers of FAAs (Variable importance in projection, VIP >1; p < .05), including tyrosine, aspartic acid, leucine, glutamic acid, citrulline, alanine, proline, glycine, and valine. Particularly, the biomarkers of FAAs were positively correlated with gram-negative bacteria (G(-)) and fungi, but negatively correlated with G(+). This is the first report to uncover the microbial communities in zaopeis, free amino acids in RL, and their correlations for Wuliangye-flavor raw liquor production.