Research On Liquid Fermentation Of Rice Wine

Rice wine,one of the traditional Chinese brewed wines,is loved by consumers because of its unique flavor.However,rice wine is mostly produced by solid-state fermentation,which is inefficient and difficult to control quality.Liquid fermentation is gradually being used to produce rice wine because of its easy quality control,easy mechanized operation.This study used single factor experiments,response surface experiments and other methods to determine the conditions for the liquefaction,saccharification and liquid fermentation of rice wine.Then,the microbial diversity and flavor substances in the liquid fermentation of rice wine were analyzed by high-throughput sequencing technology(HTS)and gas-phase high-throughput time-of-flight mass spectrometry(GC-TOF-MS).Lastly,the interaction correlation between microbial communities and flavor substances was revealed by correlation and network analysis.The preliminary sterilization conditions of rice wine were also investigated.These studies provided a certain reference for improving the quality of rice wine in the future.The main findings are as follows:(1)The conditions for liquid fermentation of rice wine were determined:liquefaction temperature 100±5?,liquefaction time 20 min and ?-amylase dosage 20 U·g^-1(calculated as glutinous rice)are the best conditions for liquefaction.Saccharification temperature 60?,saccharification time 2.5 h and glucoamylase dosage 200 U·g^-1(calculated as glutinous rice)are the best saccharification.Main fermentation temperature 27?,main fermentation time9.0 d,the inoculation amount of Saccharomyces 2.5‰,post fermentation temperature 15?and liquid material ratio 3.0 are the best fermentation condition.Under these conditions,the higher alcohol content of rice wine is 260.3 mg·L^-1,and the alcohol content is 13.0%vol.In addition,the color of wine is slightly yellow,clear and transparent,and the rice fragrant and the taste of wine is pure,typical rice wine style.(2)After the study of microbial diversity,it is found that there are 92 bacterial genera and53 fungal genera in the liquid fermentation process of rice wine.Acinetobacter,Delftia,Chryseobacterium,Weissella,Lactobacillus and Acetobacter are the dominant bacterial genera in rice wine,and Saccharomyces,Rhizopus and Wickerhamomyces are the dominant fungus in rice wine.The relative abundance of the bacterial in KEGG metabolic pathway first increased and then decreased with the fermentation.Among them,the primary metabolic pathways of KEGG are mainly Metabolism,Environmental Information Processing and Genetic Information Processing.(3)The change of physicochemical indexes and flavor substances were studied during the liquid fermentation of rice wine.Reducing sugars of rice wine continued to decrease,total acid,amino acid nitrogen and alcohol content gradually increased with the fermentation.The number of yeasts first increased and then decreased,and the number of yeast reached the maximum at the end of the main fermentation stage.In addition,72 volatile substances were detected during the fermentation process.And free amino acids gradually increased,in which Leu,Glu,Arg,Pro,Ala,Phe are the main amino acids in rice wine.Moreover,8 kinds of organic acids were detected,in which malic acid,lactic acid,acetic acid and citric acid are the main organic acids.Sensory analysis showed that the style of rice wine gradually formed with the fermentation and the wine body tended to be fuller and taste indicators such as sweet,sour,bitter and astringent weaken.(4)The network interaction relationships between microorganisms and volatile substances were revealed that bacteria and volatile substances are mainly negatively correlated and fungi are positively correlated with most volatile substances.At the same time,preliminary research on the pasteurization conditions of rice wine was conducted and it was determined that the most suitable pasteurization conditions for rice wine were 90?for 5 min.