Study On The Effects Of Non-Saccharomyces Yeast On Mijiu-Making And Its Application

Chinese traditional rice wine(Mijiu)is a traditional alcoholic beverage with thousands of years of history in China possesses its special flavor and unique production process,which has been widely favored by consumers and developed rapidly in recent years.Due to the difficulty of controlling the natural fermentation process with semi-solid substrate and diversity of microorganisms,the quality of Mijiu is unstable,which seriously affects the production of high quality and the industrialization of Mijiu.For these reasons,the use of enzyme preparations and pure yeasts for liquid fermentation of Mijiu(saccharification and liquefaction process)had been proposed in recent years,but problems such as low content of volatile compounds and bland flavor of Mijiu emerged again.In this study,based on the current development of Mijiu in China,we investigated the effects of pure fermentation of non-Saccharomyces yeast isolated from traditional Mijiu brewing and mixed fermentation with Saccharomyces cerevisiae(Sc)by different liquid fermentation processes,and investigated the mechanism of yeast interaction during mixed fermentations,so as to provide some theoretical and practical basis for the selection and improvement of liquid fermentation processes of Mijiu and the efficient production of high-quality Mijiu.The main findings of this paper are as follows:(1)Eighteen non-Saccharomyces yeast strains were isolated from Jiuyao(traditional saccharification and fermentation starter)and fermentation mash,and identified by 26 S rDNA as mainly Saccharomycopsis fibuligera(Sf)and Candida glabrata(Ca).The ethanol,glucose,temperature and p H tolerance of these two typical non-Saccharomyces yeast,Sf 2,Ca 3 and Ca 6,were examined.The results showed that the ethanol tolerance of Sf 2 was poor and that of Ca 6 was relatively strong.Other tolerance differences were not significant.(2)The fermentation characteristics of non-Saccharomyces yeast were investigated by liquid fermentation processes(saccharification and liquefaction process)under different concentration substrates.The results showed that all non-Saccharomyces yeasts had certain alcoholic fermentation ability,but lower than Sc,and had a better effect on the enhancement of volatile compounds,but there were differences in fermentation characteristics.In the low concentration substrate,Ca had a stronger ability to generate high content of volatile compounds and improve the fermentation efficiency than Sf,while Sf produced a relatively more varieties of volatile compounds.In the high concentration substrate,Ca had a stronger ability to generate volatile compounds,but had a lower efficiency than Sf.Meanwhile,the saccharification process was able to produce higher concentration of ethanol under low concentration substrate,while the liquefaction process had relatively higher fermentation efficiency and generated about 15% vol ethanol under high concentration substrate.(3)The effects of mixed fermentation of Sc and non-Saccharomyces yeast on the fermentation process and flavor of Mijiu were carried out by different inoculation methods and fermentation processes.The results showed that simultaneous inoculation could improve the fermentation efficiency of Mijiu,while sequential inoculation showed lower fermentation efficiency than Sc pure fermentation,and prolonged the fermentation time.On the other hand,the contribution of sequential inoculation fermentation to Mijiu flavor was higher than that of simultaneous inoculation fermentation,and Ca could produce higher content of volatile compounds than Sf.During the mixed fermentations,regardless of the inoculation methods,both the non-Saccharomyces yeasts were inhibited significantly.However,the Sc growth was not significantly affected in the processes.Furthermore,the results of separate fermentation of yeasts without cell-cell contact showed that the contact of non-Saccharomyces yeast with Sc was the main reason for the inhibition,which may affect the mixed fermentation performance.(4)The addition of non-Saccharomyces yeast had significant effects on the fermentation efficiency and flavor of traditional Mijiu.The treatments inoculated with Jiuyao,nonSaccharomyces yeast sequentially significantly increased the fermentation rate,and the efficiency improvement of Sf was better than that of Ca.The treatments inoculated with Ca,Jiuyao sequentially and inoculated with Ca,Jiuyao simultaneously significantly improved the volatile compounds,which increased by 2.1 and 1.5 times respectively.