Study On The Influence Of Brewing Koji And Strain On The Flavor Of Semi-solid Fermentation Rice-flavor Liquor

Rice-flavor liquor has a long history and is an important part of Chinese liquor.To a certain extent,the liquor brewing process and brewing microorganisms determine the flavor of liquor.At present,the research on rice-flavor liquor is mainly focused on the production process,and there are relatively few studies on its flavor substances.The research studies on the change characteristics of microorganisms and flavor substances during the processing of rice-flavor liquor have rarely been reported.In this thesis,the flavor characteristics of the rice-flavor liquor were studied,and the brewing process of semi-solid fermentation rice-flavor liquor was optimized.Based on the best brewing process,the change characteristics of microbial community and main flavor substances during the brewing process of semi-solid fermentation rice-flavor liquor and the correlation between the microbial community and main flavor substances were studied.The main conclusions are as follows:(1)The volatile flavor compounds in rice flavor liquor were extracted by headspace solid phase microextraction(HS-SPME)and detected by gas chromatography-mass(GC-MS).14 main volatile flavor substances of rice-flavor liquor were analyzed and quantified.Combining with odor activity value(OAV)analysis,it was found that acetaldehyde,isobutanol,ethyl acetate,n-butanol,ethyl lactate,ethyl nonanoate,nonanoic acid,isoamyl alcohol,caprylic acid,acetic acid,n-propanol,β-Phenylethanol were the important aroma component of rice-flavor liquor.Combined with the taste activity value(Do T)analysis of bitter substances in rice flavor liquor,it was found that isobutanol contributed the most to the bitterness of rice flavor liquor,followed by isoamyl alcohol.The main dizzy components of rice-flavor liquor were isoamyl alcohol,isobutanol and n-propanol.(2)Lactobacillus plantarum subsp.Plantarum CICC 6009 and Zygosaccharomyces mellis LGL-1 were used to produce semi-solid fermentation rice-flavor liquor combined with rice-flavor traditional koji.Based on the single factor test,the total ester and ethyl lactate were used as response values,the brewing process of semi-solid fermentation rice-flavor liquor was optimized by response surface test.The results showed that the best brewing process of semi-solid fermentation rice-flavor liquor was as follows: 4 ‰ laobachi koji and 7% lactic acid bacteria were added in the solid culture stage,cultivation at 36 ℃ for 46 h.120% water and 12% yeast were added,and fermentation at 32 ℃ for 16 d.Under the brewing process conditions above,the total esters and ethyl lactate were 0.46 g/L and 42.88 mg/L respectively.(3)The high-throughput sequencing technology was used to analyze the microbial community structure during the brewing process of semi-solid fermentation rice-flavor liquor.The result showed that the diversity of bacteria was greater than the diversity of fungi during the brewing process of semi-solid fermentation rice-flavor liquor.There were80 bacterial genera and 7 main bacterial genera including Bacillus,Lactobacillus,Clostridium sensu stricto 5,Weissella,Lactococcu,Staphylococcus,Acinetobacter identified during the brewing process.The addition of lactic acid bacteria and yeast reduced the diversity of bacteria,the number of bacterial genera and the main bacterial genera were reduced,and Lactobacillus became the absolute dominant bacterium in the brewing process.Five species of fungi and 3 main fungal genera including Rhizopus,Saccharomyces,Aspergillus were identified during the brewing process.During the brewing process of semi-solid fermentation rice-flavor liquor,Rhizopus and Saccharomyces were always the dominant flora.Lactic acid bacteria and yeast had little effect on the community structure of fungi.(4)The change rule of main flavor substances during the brewing process of semi-solid fermentation rice-flavor liquor was discussed.The result showed that pyruvate,acetaldehyde and organic acids were mainly produced in the cultivation stage.These three substances were rapidly consumed to produce alcohols and esters in the fermentation stage,and this process mainly occurred in the early 4～6 days of the fermentation.In the later stage of fermentation,the main flavor substances of semi-solid fermentation rice-flavor liquor slowly changed and gradually stabilized.The bitter substances and dizzy components of semi-solid fermentation rice-flavor liquor were mainly produced in the early stage of fermentation.The addition of lactic acid bacteria and yeasts during the brewing process of semi-solid fermentation rice-flavor liquor can promote the formation rate of flavor substances.Alcohols and bitter substances reached the highest value 3 days in advance.Ethyl lactate had started to accumulate during the saccharification stage.However,the addition of lactic acid bacteria and yeasts did not affect the content of main flavor substances in semi-solid fermentation rice-flavor liquor.(5)Cytoscape software was used to analyze the correlation between the main flavor substances and the microbial flora,and it was found that the influence of the same microorganism on the flavor substances in different microbial environments was different and cannot be generalized.Among them,the same microorganism in different microbial environments had consistent effects on flavor substances,including Weissella and isobutanol were positively correlated,Bacteroides were positively correlated with acetaldehyde and nonanoic acid,Acinetobacter was negatively correlated with lactate,Bacillus and ethyl lactate was positively correlated,Lactobacillus was negatively correlated with ethyl lactate.