The Mechanism Of N-butanol Synthesis In The Process Of Chinese Strong Aroma Baijiu Fermentation And Solutions For Control And Reduction Of It In Baijiu

Higher alcohols(Has)are one of the important flavor components in Chinese strong aroma baijiu,which has critical influence on spirits quality and drinking feelings.The proper content of higher alcohols can enhance the richness and balance of spirits.However,high level of HAs causes headache,dizziness and other adverse reactions upon consumption.N-butanol is one kind of higher alcohols in Chinese strong aroma baijiu.Its taste is bitter and slightly astringent.Thus it may affect the taste if the content of butanol is too high in spirits.Therefore,controlling the content of n-butanol is very important to improve the quality of spirits.Uncovering the mechanism of n-butanol synthesis during Chinese strong aroma baijiu fermentation is of great significance for regulation of butanol synthesis.This study focuses on fermented grains of Chinese strong aroma baijiu.Correlation analysis and fermentation verification were used to reveal the microbial strains related to the production of n-butanol,and the synthesis mechanism of n-butanol was clarified by investigating the butanol production capacity of the strains and the analysis of metabolic pathways.In addition,production of n-butanol during spirits fermentation.The main results are as follows:(1)Synthesis of n-butanol and related microorganisms in the process of Chinese strong aroma baijiu fermentation.There were two n-butanol synthesis stages: 14?21 d and 28?42 d.Pearson correlation analysis of the production of n-butanol and microorganisms from fermented grains showed that Caproiciproducens and uncultured?bacterium?f?Clostridiaceae?1 were significantly positively correlated with the production of n-butanol.By comparing the differences in the microbial composition of the pit mud of the three types of cellars with high,medium and low n-butanol content in baijiu,it was preliminarily determined that the microorganisms related to the synthesis of n-butanol in the fermentation process of Chinese strong aroma baijiu are Clostridium strains mainly come from the pit mud.(2)Uncovering mechanism of n-butanol synthesis in the process of Chinese strong aroma baijiu fermentation.Strains belonging to eight species of Clostridium,including Clostridium beijerinckii and Clostridium tyrobutyricum,were isolated from the pit mud of Chinese strong aroma baijiu.Among them,Clostridium beijerinckii showed the strongest capability to synthesize n-butanol,which was 1 013?8 956 times of that synthesized by other Clostridia.In addition,by strengthening the Clostridium in the spirits solid-state fermentation system,it was found that the fortified Clostridium beijerinckii ignificantly increased the butanol content up to 3.57 times in fermented grains.The more Clostridium beijerinckii in the pit mud,the higher n-butanol content was detected.The main pathway for Clostridium beijerinckii to synthesize n-butanol is the one via the glycolysis(Harris pathway).(3)Control and reduction of n-butanol synthesis during spirits fermentation by interfering with Clostridium from pit mud.In this study,a strain of Clostridium tyrobutyricum ZY-4,which was suitable for regulating the production of n-butanol in spirits solid-state fermentation,was selected from high-quality pit mud with low n-butanol production.Clostridium tyrobutyricum ZY-4 produced acetic acid and butyric acid via branch metabolic pathways,thus reduced the n-butanol synthesis of Clostridium beijerinckii.Addition of Clostridium tyrobutyricum ZY-4 in a simulated Chinese baijiu fermentation system reduced the synthesis of n-butanol by up to 30.05%.And the content of ethyl caproate and ethyl caprylate(the backbone flavor substances)in Chinese strong aroma baijiu increased by25.77% and 22.22%.No significant effect on the production of most of the main volatiles was detected.