The Dynamic Diversification Of Bacterial Functional Groups And The Flavor Producing Bacteria In The Baiyunbian Liquor Stacking Fermentation Process

As a typical representative of Chinese Maotai-Luzhou flavor liquor,the Baiyunbian liquor stacking fermentation(SF)process learns from the production process of Maotai flavor liquor,which act as a bridge between Daqu making and alcoholic fermentation in the pits.Revealing the dynamic diversification of the bacterial functional groups in this process is of vital importance to unfold the mechanism of Baiyunbian liquor flavor,and improve the quantity and production of traditional Chinese liquor fermentation process.Total of 8 kinds of functional groups were screened by the sole carbon source media and 142 strains of bacteria were isolated from the Baiyunbian liquor SF process,which were divided into 17 species and 2 subspecies.These isolated bacteria could hydrolyze the main carbon resources such as starch,protein,cellulose,lignin and fat as well as produce acetic acid,lactic acid or butyric acid.The starch degrading bacteria possessed the largest biomass of all the fuctional groups.The biomass trend to increase slowly at the beginning and then rapidly to the maximum,after which it decreased slightly.Interestingly,although the bacterial bio-diversity decreased during the SF process,the total bacterial biomass increased at the end,in which the biomass of the starch degrading bacteria was presented dominantly throughout the whole SF process.Through the enrichment,screening and domestication of SF,the beneficial microorganisms were largely enriched while the harmful microorganisms were died at last.Our results indicated that the dynamic variations of the bacterial functional groups revealed their specific functions in the Baiyunbian SF process.It was these functional groups that provided the sufficient fermentation activity for the alcoholic fermentation and contributed to the Baiyunbian liquor flavor formation.Among the identified bacteria,B.licheniformis and B.subtilis contributed the most biomass and functionalities during the Baiyunbian SF process,playing important roles in the formation of the Maotai-flavor and could also produce tetramethylpyrazine.Tetramethylpyrazine is the most important flavor compounds and health factors in Chinese liquor,which can largely impact the liquor quality.Olfactometry was used to screen the solid fermentation products of 98 flavor producing strains with special flavor.Totally 7 strains were selected to analysed the liquid/solid fermentation products by Gas Chromatography and Mass Spectroscopy.The results showed that,liquid fermentation produced hydrocarbons and acids mostly while solid fermentation produced more contents and kinds of pyrazines including tetramethylpyrazine,and B.Subtilis RS51 had a stronger ability to produce tetramethylpyrazine.The diferences between liquid/solid fermentation products indicated that,the stable cindition of solid fermentation is more likely to produce flavor compounds,and the condition of stacking fermentation is beneficial to the transformation of precursor substances to flavor components.Our study revealed the bio-diversity of the bacterial functional groups in the Baiyunbian liquor SF process and the mechanism of the Baiyunbian liquor flavor formation,providing valuable guidance to improve the traditional Chinese liquor fermentation process and development healthy liquor.It could also act as an attempt to turn the experienced manufacturing process to standardized procedures.