Study On Improving The Content Of Characteristic Aroma Substances In Rice Wine By Screening Multi-strain Fermentation

Chinese liquor is brewed in an open environment.Many different kinds of microorganism and the interaction among them affect the quality of liquor.Therefore,the study of interactions between microorganisms can help understand the mechanism of action of various microorganisms in liquor brewing,and contribute to further regulate the species and quantity of microorganisms in the process of liquor brewing with the purpose of raising the content of targeted components in liquor.In addition,the flavoring liquor needs to be produced to increase the aroma,for the content of some flavor compounds are low in the brewing process of liquor,so as to improve the quality of liquor.This paper centered on three flavor compounds in the rice wine,which are ethyl acetate,ethyl lactate and ?-phenylethanol respectively.The interaction between Saccharomyces cerevisiae and Acetobacter pasteurianus was investigated under liquid fermentation conditions.At the same time,the effects of mixed strains fermentation on rice wine flavor compounds were investigated,and a kind of flavoring liquor of high ?-phenylethanol was developed by two-step process.The main results were as follows:1.The interaction between S.cerevisiae and A.pasteuriae was studied.The results indicated that A.pasteurianus have small impact on the growth and metabolism of S.cerevisiae in the early stage of the fermentation in Synchronized mixed inoculation.Besides,the alcohol fermentation of S.cerevisiae in anaerobic environment inhabited the growth of A.pasteurianus and the synthesis of ethyl acetate in the mixed culture.At the late stage of the fermentation,the growth of A.pasteurianus and the production of acetic acid accelerated the decay of S.cerevisiae,but promote the synthesis of ethyl acetate,with the highest content of 595.72 mg/L,which was 10.1 times compared to the pure fermentation of S.cerevisiae.In sequential mixed inoculation,the content of ethyl acetate also increased significantly up to 341.54 mg/L,but it was lower than Synchronized mixed inoculation;inoculating A.pasteurianus after 24 h had greatest impact on the metabolism of S.cerevisiae,and its alcohol content decreased by 22.98% than the control group.And the content of ethyl acetate in the sequential inoculation was lower than that in the synchronous inoculation modes.A.pasteurianus was inoculated synchronously in rice wine by semi-solid fermentation medium.At the end of the fermentation,the content of ethyl acetate reached 1666.99 mg/L in rice wine,which was increased 21.7 times than that in the control group.The content of acetic acid increased by 11.5 times,and the content of acetaldehyde decreased by 36.59%.2.Aspergillus niger and Rhizopus oryzae were acted as saccharifying agent when S.cerevisiae,Lactobacillus plantarum and A.pasteurianus were added to rice wine fermentation system.Single factor experiment was conducted to optimize distiller's yeast added proportion,malt content,L.plantarum inoculum,liquid saccharifying enzyme content,fermentation time and A.pasteurianus inoculum,then a orthogonal experiment was designed to get the optimal fermentation conditions.The optimal fermentation conditions were: distiller's yeast added proportion 3%(g/g),liquid saccharifying enzyme 0.01%(V/mL),fermentation time 12 d and A.pasteurianus inoculum 0.01%(V/g).The results of the experiments according to this optimized condition were as follows: the alcohol content changed from 45.4%vol to 47.6%vol,increasing by 4.85%;the ethyl acetate content increased from 165.93 mg/L to 629.35 mg/L,a 2.8-fold increase;ethyl lactate content changed from 147.63 mg/L to 245.73 mg/L,an increase of 66.45%;?-phenylethanol content was 79.24 mg/L,basically unchanged.The results showed that the quality of rice wine was improved significantly.3.?-phenylethanol flavoring liquor was developed by UV mutant,aerobic fermentation and two-step process of feeding anaerobic fermentation for the advance the quality of rice wine which is based on previous research of synthesizing ?-phenylethanol with L-phenylalanine by S.cerevisiae.A mutant strain UV-15-15 was screened out by two-round UV-induced mutagenesis when S.cerevisiae GIM2.35 as original strain.Its ?-phenylethanol synthesis ability increased by 13.6% compared to the original strain.The results of single factor experiments showed that the optimal aerobic fermentation condition was wort 11°P,L-phenylalanine 5 g/L,fermentation time 24 h;the optimum feeding anaerobic fermentation conditions were feeding ratio 1:4,feeding solution L-phenylalanine 5 g/L,A.pasteurianus inoculum 3%(V/V),fermentation time 8 d.After fermentation,the alcohol content of the distilled liquor was 11.2%vol,acetic acid content was 0.37 g/L,?-phenylethanol concentration was 1.17 g/L,and the sensory evaluation score was 8.9.In addition,using the distiller's yeast as saccharification and fermentation agent,high ?-phenylethanol rice wine fermentation process optimization conditions were static saccharification time 6 h,aerobic fermentation time 18 h,anaerobic fermentation medium L-phenylalanine 1 g/L.The yield of ?-phenylethanol was 1.13 g/L after the fermentation,reaching a target of 1.00 g/L or more.