Characterization Of The Structure And Function Of The Microbial Community In Light Aroma Type Liquor Started By Xiaoqu

Light aroma type Xiaoqu liqour is an important componet of Daqu liqour, and microorganisms in Xiaoqu liqour have different brewing characteristics from that in Daqu liqour. Studying the function, metabolic characteristics and interaction of microorganisms in Xiaoqu liqour, not only have great significance to enrich the research of microorganisms in Chinese liquor, but also have positive and practical value to reform and improve traditional methods in Xiaoqu liqour.Xiaoqu and fermented grains in light aroma type liqour were analyzed for bacteria, yeast and fungi diversity by PCR-DGGE. Extracted DNA was used as a template for PCR to amplify 16S rRNA gene V3 region, 26S rRNA gene D1 region and 18S rRNA gene partial region using universal primers. The main key microorganisms were determined combining culture-dependent and culture-independent methods. Using liquid culturing, physiological, metabolic characteristics of key microorganisms and yeast interaction were measured. Through sutiable inoculation strategy of yeast, content of ethyl acetate increased on the basis of ensuring fermentation efficiency. Mixed fermentations of mold and yeast in solid state have been achieved at last.The result indicated that1) Microbial community in light aroma type Xiaoqu liqour was analyzed by PCR-DGGE, firstly. There was high diversity of bacteria in Xiaoqu and fermented grains, and lactic acid bacterias and Bacillus were dominant groups. Main yeast included Saccharomycopsis fibuligera, Pichia anomala and Saccharomyces cerevisiae. Only Rhizopus oryzae was predominant mould. Although there were differences in growth and death of microorganism, microbial compositions in fermented grains collected in different seasons appeared no significant change. With counting results of yeasts, S. cerevisiae and P. anomala were main alcoholic fermentation and ester-producing yeasts.2) In sorghum juice medium P. anomala grew slowly and required almostly 10 h intervals to achieve the same biomass of S. cerevisiae. Fermentation capacity of yeast declined with increasing ethanol concentration and alcohol tolerance of S. cerevisiae was higher than that of P. anomala. P. anomala had better ability to produce ethyl acetate in sorghum juice medium than that in GPYM or YPD medium. Although the inoculum percentage of P. anomala affected the production of ethyl acetate in the initial stage of fermentation, the content was similar at the end of fermentation.3) Mixed fermentation of S. cerevisiae and P. anomala in sorghum juice medium were investigated. Comparing with monoculture or mixed inoculation of S. cerevisiae/P. anomala, growth of P. anomala wasn't inhibited by S. cerevisiae and two species could reach high biomass using sequential inoculation. At the end of sequential fermentation, ethanol content was 20.17 g/L, which was reduced by 9% than pure culture of S. cerevisiae. The concentration of ethyl acetate was 0.74 g/L, which was increased by 80% compared to P. anomala monoculture. The mixed fermentation of S. cerevisiae and P. anomala produced more esters, less alcohols and fatty acids, and improved flavor characteristics of fermentation products.4) 10⁵ conidia mL^-1 of spore suspension of R. oryzae was inoculated in sorghum medium. After saccharifying 1 d at 30℃, 10⁷ CFU mL^-1of S. cerevisiae and P. anomala seed liquid were inoculated again. As a control, heat-resistantα-amylase and glucoamylase instead of R. oryzae completed saccharification. The concentration of ethanol and ethyl acetate in mixed femrnteation of S. cerevisiae, P. anomala and R. oryzae were always higher than that in the control during the fermentation process, which were increased by about 13 times and 1 times at the end of fermentation, respectively. Comparing with the fermentation of Tuqu, the content of alcohols were decreased by 53% and total content of esters increased by about 1 times.