| Rice wine is one of the three ancient wines in the world and the oldest fermented wine in China.In recent years,with the improvement of consumers’sensory requirements for rice wine,it is still very meaningful to study the fermentation bacteria,process improvement,and flavor changes of rice wine during fermentation.In this project,Saccharomyces cerevisiae and Hansenula anomala were used as rice wine fermentation strains to investigate the effect of compound yeast on the fermentation process and product flavor of rice wine.Combined with physical and chemical indicators such as sensory evaluation and alcohol content,a suitable Mixed bacteria fermentation route of rice wine fermentation.The main conclusions are as follows(1)Comparing the fermentation performance of the two yeasts,the initial fermentation sugar content was 18 Brix,the results showed that the alcohol content of Saccharomyces cerevisiae reached the highest content of 10.7vol%after 7 days,and the alcohol content of abnormal Hansenulae reached the highest content of 7.3vol%after 16 days.Saccharomyces cerevisiae is stronger than non-Saccharomyces cerevisiae.On the 16th day,the volatile ester content of Saccharomyces cerevisiae and Hansenula anomaly reached the maximum value,which were 0.56g/L and 2.67g/L,respectively.The volatile ester content of Hansenula anomaly was 4.8 times that of Saccharomyces cerevisiae.The volatile ester content of Hansenula yeast was significantly higher than that of Saccharomyces cerevisiae,and the aroma was more intense.(2)Through the experimental study of mixed bacteria fermentation,after the fermentation,the alcohol content of sequential mixed fermentation(8.1vol%)was slightly lower than that of simultaneous mixed fermentation(8.7vol%),and the content of volatile esters(1.59g/L)was significantly higher than that of simultaneous mixed fermentation.(0.56g/L),indicating that sequential mixed fermentation can better reflect the fermentation advantages of non-Saccharomyces cerevisiae than simultaneous mixed fermentation.Combined with sensory evaluation and physical and chemical indicators such as volatile esters,it is concluded that the sequential mixed fermentation route is better than the simultaneous mixed fermentation route.Next,the effects of different ventilation rates on sequential mixed fermentation were compared.The results showed that different ventilation rates had significant effects on the proliferation of Hansenula anomalies,and the highest proliferation number was SH180(3.26×10~8cfu/m L)>SH100(1.72×10~8cfu/m L)>SH(6.9×10~7cfu/m L),After the fermentation,the alcohol content was SH180(8.3vol%),SH100(8.7vol%),and SH(8.1vol%);the volatile ester content was SH180,(1.66g/L),SH100(1.64g/L),SH(1.59g/L).Combined with physical and chemical indicators such as volatile esters and sensory evaluation,it is more appropriate to choose the sequential mixed static fermentation route.(3)Through the single factor and Box-Benhnken center combined experimental design,three factors of main fermentation temperature,p H value and yeast inoculum were selected for response surface optimization.The results showed that the order of factors affecting the content of volatile esters was:A(main fermentation temperature)>C(inoculation amount)>B(p H value).The inoculum amount was 0.93×10~7/ml,the p H value was 4.18,and the predicted theoretical value was 1.70g/L.C it is suggested that the actual operation of the factory can be adjusted to the fermentation temperature of 31.5°C,the inoculum volume of 1.0×10~7/ml,and the p H value of 4.2.Under these conditions,the volatile ester content of the mixed-sequentially fermented rice wine was 1.66±0.028g/L,which was not much different from the predicted value of 1.70g/L.(4)HPLC and HS-SPME-GC-MS were used to determine the organic acids and volatile components of the mixed sequential fermented rice wine and the traditional The results showed that the organic acid content of sequential mixed fermented rice wine(1028.5 mg/L)>traditional Saccharomyces cerevisiae fermented rice wine(1002.3 mg/L),esters(a total of 11species)and content(235.29 mg/L)were significantly higher than those of traditional brewing.Yeast-fermented rice wine,by comparing the flavor components of the two fermentation processes,it can be seen that the sequential mixed fermentation process can effectively improve the aroma components and flavor of rice wine.To detect the volatile components of the sequentially mixed rice wine in different periods,and a total of 47 kinds of compounds were detected,including 10 kinds of alcohols,16 kinds of esters,12 kinds of acids,4 kinds of aldehydes,2 kinds of olefins,and phenols.2 kinds of substances,1 kind of ketones.Combined with principal component analysis(PCA)and cluster analysis(HCA),the volatile substances were statistically analyzed,and the fermentation process of rice wine was divided into three stages,namely the pre-fermentation(1-4d)and the middle-fermentation(7-15d),late fermentation(20d).Then combined with the factor loading diagram,the characteristic aroma components of different fermentation stages can be known.Finally,through partial least squares discriminant analysis(OPLS-DA)combined with variable projection importance(VIP)analysis,we obtained ethyl acetate(B1),phenethyl alcohol(A5),isoamyl alcohol(A4),isobutyl acetate(B14),octanoic acid(D4),these five volatile components can be used as important volatile substances to distinguish different fermentation stages. |
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