Screening Of Non-Saccharomyces Cerevisiae With High Ester Yield And Its Fermentation Characteristics In Mixed Fermentation

The mixed fermentation of non-Saccharomyces cerevisiae and Saccharomyces cerevisiae has been proved to improve the types and contents of volatile substances in wine and fruit wine.Because of its good environmental tolerance,Torulaspora delbrueckii has attracted much attention,which has a positive impact on the flavor quality of alcohol.Making full use of local non-Saccharomyces cerevisiae resources and rationally using the mixed fermentation strategy of non-Saccharomyces cerevisiae and Saccharomyces cerevisiae can improve the flavor quality of liquor to some extent.15 strains of yeast were isolated from Luzhou-flavor liquor pits in the early stage of the laboratory.By comparing the ester-producing and ethanol-producing properties of different species of non-Saccharomyces cerevisiae,the characteristics of their mixed fermentation with Saccharomyces cerevisiae were investigated.Torulaspora delbrueckii with high ester yield was obtained,and the interaction between mixed fermentation microorganisms and its influence on the formation of volatile substances in fermentation system were explored.The main conclusions are as follows:(1)With the total ester as the index,15 strains of non-Saccharomyces cerevisiae were preliminarily screened,and four strains of non-Saccharomyces cerevisiae were obtained,including Hanseniaspora uvarum F3,Torulaspora delbrueckii F4,Pichia fermentans F8 and Hansenula anomala F12;Taking ethanol as an index,three Saccharomyces cerevisiae strains were screened to obtain a Saccharomyces cerevisiae strain with high ethanol yield S15.The mixed fermentation of non-Saccharomyces cerevisiae and Saccharomyces cerevisiae which had been screened in different ways was re-screened.All six yeasts were tolerant to p H 3.0and ethanol content of 10%vol,and the total acid and total ester contents of Torulaspora delbrueckii F4 and Saccharomyces cerevisiae S15 were higher after sequential mixed fermentation,which were 6.5 g/L and 12.82 g/L respectively.Therefore,in the follow-up experiment,round Torulaspora delbrueckii F4 and Saccharomyces cerevisiae S15 were selected for sequential inoculation and mixed fermentation.(2)Preferably,Torulaspora delbrueckii F4 and Saccharomyces cerevisiae S15 are mixed and cultured.The results showed that the total acid content increased first,then decreased and then increased during fermentation.The change of total ester content showed an upward trend with the fermentation time,and in 4-5 days,the mixed fermentation exceeded that of single fermentation.With the extension of fermentation time,the reducing sugar in fermentation broth has been decreasing,and the reducing sugar content is less than 4 g/L after fermentation.The ethanol content in the fermentation broth increased with the increase of fermentation time.At the end of fermentation,the ethanol content was D4(15.861%vol),D15(19.718%vol)and H4(10.821%vol)in turn.With the continuous extension of fermentation time,the p H of the fermentation broth decreased,then increased and then maintained a stable trend,and the p H after fermentation was basically the same.The fermentation kinetics model can predict the state in the fermentation process and build the model of substrate consumption in the fermentation process.The results show that the model has high fitting,which can be used to study the substrate consumption process of strains.(3)HS-SPME-GC-MS technology was used to determine and analyze the volatile substances in single and mixed fermentation of Torulaspora delbrueckii F4 and Saccharomyces cerevisiae S15.There are 24 kinds of esters in mixed fermentation,and the content(12.832 mg/L)is almost higher than that in single-strain fermentation.In this study,the content of esters was obviously increased by mixed fermentation,and the types of esters in fermentation broth were increased,which provided some data reference for the flavor enhancement of mixed fermentation of non-Saccharomyces cerevisiae and Saccharomyces cerevisiae.(4)The effects of mixed fermentation of Saccharomyces cerevisiae S15 and Torulaspora delbrueckii F4 with different inoculation ratios on volatile components were studied.When the inoculation ratio was 1:1,the species and total content of volatile substances were the highest(96.059 mg/L),followed by 1:10(43.575 mg/L)and 1:5(30.904 mg/L).The total amount of higher alcohols decreased with the increase of the proportion of Torulaspora delbrueckii,but the esters increased with the increase of the proportion of Torulaspora delbrueckii.The above results provide some guidance for the application of Torulaspora delbrueckii in mixed fermentation research,which is beneficial to improve the flavor substances of alcohol.