Chemotaxis And Metabolic Characteristics Of Clostridium Strains Isolated From Strong Aroma Baijiu Pit Mud

Strong aroma baijiu is a popular baijiu type and its quality is closely related to pit mud.Microorganisms in pit mud had an important influence on the formation of strong aroma baijiu flavor substances.Among them,Clostridia can synthesize butyric acid,caproic acid and other key flavor substances,which are important functional microflora in pit mud.Clostridium did not only exist in the pit mud,but also migrate to the fermented grains to participate in the pit fermentation with the change of the conditions in the pit.However,the reasons why Clostridium migrated to fermented grains and what factors affected its migration were not clear.Therefore,in this study,based on the analyzed the differences of microbial community structure,physicochemical properties and volatiles in pit mud as well as the correlation among them.The metabolic characteristics of flavor substances,motility and chemotaxis of Clostridium were analyzed.It can provide theoretical reference for elucidating the mechanism of Clostridium in liquor fermentation.The main results of this paper are as follows:(1)Characterization and correlation analysis of the physicochemical properties,bacterial composition and volatiles in baijiu fermentation pit mud of different ages.Moisture,available phosphorus and potassium,and the key flavor volatiles(caproic acid,ethyl caproate,and ethyl butyrate)in mature pit mud(30 years)were higher than those in growing pit mud(10 years),whereas lactic acid and hexanol showed the opposite trend.The indexes of pit wall mud and bottom mud of the same pit age are close.Proteiniphilum and Petrimonas(Bacteroidia)were most abundant in growing pit mud,whereas Caproiciproducens and Clostridium(Clostridia)were most abundant in mature pit mud.The relative abundance of Clostridia(Caproiciproducens and Clostridium)was positively correlated with the content of caproic acid and ethyl caproate,and negatively correlated with the content of lactic acid.The physicochemical properties of pit mud influenced most species of Clostridia in pit mud.Moisture and available phosphorus and potassium were positively correlated with the content of key volatiles and the relative abundance of Clostridia.(2)Analysis of metabolic characteristics and motility of Clostridium.110 strains of Clostridium in 15 species were isolated from pit mud,among which Clostridium tertium,Clostridium pabulibutyricum and Clostridium intestinale were isolated from strong aroma baijiu pit mud for the first time.The metabolites of the 15 representative strains of Clostridium showed that they all had the ability to produce acids,alcohols,esters,phenols,aldehydes and other substances in different degrees.In addition,the motility analysis of 110 strains of Clostridium showed that 81% of them had motility.(3)Chemotaxis of Clostridium mucilage and its application.A qualitative method of chemotaxis of Clostridium was established by using semi-solid agar plate method.Using this method,Clostridium showed chemotaxis to organic acids such as lactic acid and acetic acid,L-cysteine,glutamic acid,glucose and other substances.The metabolites of 8 Lactobacillus including Lactobacillus pentosus,Lactobacillus paracasei and Lactobacillus plantarum were chemotaxis.In the simulated liquor fermentation system,the addition of the chemotactic agent lactic acid promoted the migration of Clostridium from the low lactic acid area to the relatively high lactic acid concentration area,effectively reduced the lactic acid content in the pit mud of the corresponding area and increased the contents of acetic acid and butyric acid.