| Distiller's grains is the main by-product in Baijiu production,rich in nutrients and flavor substances.How to make effectively use of liquor distiller's grains is of great significance to China's liquor industry development and environmental protection.The paper use pure culture high-yield esters,low-yield higher alcohol Saccharomyces cerevisiae and complex enzyme saccharification and fermentation.Optimize the process of re-fermenting distiller's grains by adding new grains to achieve synchronization of liquor production and fragrance.While using pure culture of lactic acid bacteria and the liquor tail biosynthesis ethyl lactate,produce high-quality Laobaigan liquor,achieve the resource utilization of by-product in Baijiu brewing.The main research contents and results are as follows:(1)By studying on the determination of main acids and esters in the fermented grains of fen-flavor liquor by HPLC,the method of simultaneous determination of lactic acid,acetic acid,ethyl lactate and ethyl acetate in fermented grains by HPLC was established.The results showed that lactic acid,acetic acid,ethyl lactate and ethyl acetate have good linear relationship in a certain range,the correlation coefficient R2>0.9991,and the relative standard deviation(RSD)?2.5%,which has high accuracy and stability.The fermented grains was tested by static extraction with 10%(v/v)ethanol solution for 30 min.It was found that the recovery rates of the four substances were between 93.2%and 104.9%,which was satisfied with the requirements of quantitative detection of the Laobaigan fermented grains.(2)The recombinant strain MY-12 was constructed with overexpressing the alcohol acetyltransferase encoding gene ATF1 and knocking out the ester hydrolase encoding gene IAH1.The results showed that compared with the parent strain AY-12,the fermentation characteristics no obvious distinctions,the ethyl acetate content increased by 20 times,the isoamyl acetate content increased to 49.74 mg/L,higher alcohols reduced by 45.0%.(3)Optimized the process of re-fermenting distiller's grains by adding new grains.The results showed that the optimum fermentation conditions:the ratio of sorghum and distiller's grains was 1:3.0,the inoculum concentration of MY-12 yeast was 0.3 billion/g,and the amount of added acid protease was 30 U/g,KH2PO4 0.18 g/100g,MgSO4 0.14 g/100g,and the fermentation time was 21 days.Under this fermentation conditions,the quality and yield of Baijiu had a big promotion.Whereas the alcohol content in the fermented grains was up to 8.0%(v/w),which is 3-4 times of the alcohol content in the fermented grains of Sancha,and the contents of the main flavor substances ethyl acetate,ethyl lactate and higher alcohol were 16.7 mg/100g,41.7 mg/100g and 14.1 mg/100g,respectively,also the residual starch was reduced by two percentage points compared with the fermented grains of Sancha.(4)Optimized the process of the Lactobacillus casei lactic acid fermentation and the synthesis of ethyl lactate with the liquor tail and lactic acid fermentation broth by Candida antarctica lipase B(Nov-435).The optimal fermentation conditions for Lactobacillus casei:the sugar content of fermentation medium was 12 g/100mL,temperature was 35?,inoculum volume was 10%,after 15 days,the content of lactic acid was 86.02 g/L;The optimum process of high ethyl lactate esterification solution:the volume ratio of 40%vol liquor tail and lactic acid fermentation broth of was 1:1,pH=3.0,the content of enzyme was 0.5%,temperature was 30?,after 21 days,the ethyl lactate content could be to 12.05 g/L.(5)By studying on the application of esterification liquid in Baijiu production found that:the optimum alcohol content of liquor flavor was 45%vol,whereas not only a relatively high content of lactate(17.62 g/L),also the liquor is clear and ester fragrance;Adding the esterified liquid which is equivalent to 10%of the amount of the fermented grains,the amount of ester-flavored substances in the base liquor reached the level of Laobaigan Dacha and Ercha liquor. |
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