Filamentous Fungal Community Structure And Interaction Between Filamentous Fungi And Yeast Associated With Chinese Maotai-flavor Liquor Fermentation

The unique fermentation process of Maotai-flavor liquor has shaped a special microbialcommunities. Within the microbial community, filamentous fungi can secrete a variety ofenzymes and metabolites, which has an important impact on the simultaneous saccharificationand fermentation process and the formation of liquor flavor compounds. Due to the limitationof research methods, the knowledge about the structure and function of fungal communityduring Maotai-flavor liquor fermentation process is still very limited. This study hascombined the culture-dependent and-independent methods to analyze the structure anddiversity of the fungal community, and the functional filamentous fungi associated with theMaotai-flavor fermentation process. Compared the growth and enzyme-producing traits ofseveral fungal strains under different fermentation conditions, we screened the strains withgood quality and studied the interaction between the filamentosu fungi and S. cerevisiae. Inthe end, we applied and tested the strain with the production practice.The main findings are as follows:1) Eight and seven different fungal species were identified by using culture-dependentand-independent methods (PCR-denaturing gradient gel electrophoresis, DGGE) analysis,respectively. The traditional enumeration method showed Daqu provided7fungal species forstacking fermentation. The total population of filamentous fungi increased from3.4×103cfu g-1to1.28×104cfu g-1in the first3days of stacking fermentation, and then decreased tillthe end. Therefore, stacking fermentation is an essential stage for growth of filamentous fungito grow. Paecilomyces variotii, Aspergillus oryzae, and Aspergillus terreus were detected byboth methods, and P. variotii and A. oryzae were the dominant species. Meanwhile, A. oryzaeand P. variotii possessed the ability to yield high α-amylase and glucoamylase activities. Theα-amylase and glucoamylase activities of P. variotii were3,252U g-1and1,417U g-1, and theglucoamylase and α-amylase activities of A. oryzae were2,463U g-1and1,491U g-1.2) The Real-time PCR methods were established and the effectivity was firstly validatedin a simple microbial fermentation system. Then the methods were applied in the complexMaotai-flavor liquor fermentation process. The biomass of P. variotii and A. oryzae wereaccumulated and reached the peak of1.44×104spores g-1and6.15×103spores g-1, respectively.Furthermore, the variation of starch and reducing sugar content was consistent with thegrowth of P. variotii and A. oryzae in Zaopei (fermented grains) during stacking fermentation,which implied the two filamentous fungi played an important role in producing amylase forhydrolyzing the starch.3) A. oryzae XJ10and Saccharomyces cerevisiae were mixed and fermented, themaximum ethanol content was obtained under the initial sugar content of200mg g-1,30Cand pH4.5conditions. Then A. oryzae XJ10and S. cerevisiae were mixed and fermented withdifferent biomass ratio, and ethanol production of mixed fermentation were higher thancontrol group for50~70mg g-1with more yeast biomass. Furthermore, mixed fermentationcan increase the concentration of esters, acids, alcohols, aldehydes, ketones and other flavorcompounds, especially for those important flavor compounds, such as acetate, ethyl benzene, 3-methyl-butanol, acetic acid, which were higher than the control group for4~100times.4) S. cerevisiae and A. oryzae XJ10were made into Fuqu and mixed at the ratio of1:0.5,1:1,1:1.5,1:2before the fermentation. The liquor yield rate of4groups were21.23%,24.50%,27.09%and27.90%, respcetively. The tasting panel marked scores based on theliquor aroma and taste, and the scores were31,31,41and46(out of56points), respectively.When the mixing ratio was1:2, the liquor yield rate improved significantly and maintainedthe best flavor and taste of liquor, which improved the production efficiency.