The Origin Study Of Off-odor Compound P-cresol In Chinese Strong Aroma Type Liquor

It is a complex system of volatile flavor compounds and microbes in Chinese liquor. Studying corresponding relationship between volatile flavor compounds and microbes is import to improve the quality of liquor. Pit mud odor is a common peculiar smell in strong aroma Chinese liquor, which is mainly caused by p-cresol(PC). In order to identify the source of pit mud odor, and provide the theoretical foundation for controling PC content in liquor, the change rule of PC in brewing process, the microbial structre in pit mud, the microbial source of PC, and the influence of nutriment for producing PC were analyzed and studied.The main research contents and results are as follows:(1) PC content were detected in saccharogenic sorghum, Daqu and pit mud, and PC was mainly from pit mud. PC content in pit bottom was higher than in pit wall. Fermented grains could produce little PC. Microorganism in pit mud could produce PC; hunagshui soaked pit mud and PC was dissolved in huangshui; huangshui was contacted with fermented grains while huangshui rised; PC was into fermented grains; fermented grains were distilled after fermentation and PC was into base liquor.(2) PC content increased from upper pit mud to bottom pit mud in pits. The microbial communities of different parts of pit muds were detected by high throughput sequencing technology. The bottom pit mud had higher microbial richness than upper pit mud. The microbes belonged to 21 phyla, 41 classes and 108 genera. Firmicutes and Bacteroidetes(>90%) dominated pit mud. PC was positive correlation(>0.95) with Syntrophomonas, Caloramator, Clostridium, Tepidimicrobium, Sporanaerobacter and Coprococcus by EXCEL CORREL function. The six genera all belonged to Clostridiales, and were most likely the main microbial source of PC.(3) Pit mud was cultured by hexanoic acid bacterium medium, reinforced Clostridium medium and beef extract-peptone medium. Clostridium dominated fermentation liquor. Base on the PC concentration and microbial structure of three mediums, C. tyrobutyricum, C. sporosphaeroides, C. amylolyticum, C. swellfunianum and C. mangenotii may produce PC. C. subterminale, C. populeti, C. acetobutylicum, C. amylolyticum, C. argentinense and C. sporogenes could not produce PC.(4) 34 strains were isolated from pit mud. 11 species were identified by 16 S r RNA. 4 species could produce PC, Eubacterium contortum, C. tyrobutyricum, Clostridium butyricum and Clostridium aminovalericum. Clostridium accounted for 5.23% in the bottom pit mud. PC mianly was produced by Clostridium and C. tyrobutyricum was one of the main microbial source. Strains which could produce PC also produced other important flavor substances, for example, butyric acid, caproic acid, acetic acid. Phylogenetic analysis revealed that strains belonged to Clostridia Cluster I. Fe2+ and ethanol could promote mixed microbes in pit mud to produce PC.(5) Pit mud and huangshui contained some tyrosine and phenylalanine. Correlation analysis showed that PC had positive correlation with free tyrosine. PC content increased after adding tyrosine into medium. Tyrosine may be main precursor to produce PC.