Isolation,Identification And Application Of Mould In Daqu Of Nongxiangxing Baijiu

Daqu is an important prerequisite for the production of nongxiangxing baijiu.The mould community in Daqu,as the dominant flora,can produce a large number of extracellular enzymes and flavoring products in the fermentation process,which can be used as saccharifying agent,starter and flavoring agent in the fermentation process.Therefore,it is necessary to isolate and identify the mould in Daqu,screen the mould with high yield of esterification enzyme,glucoamylase and acid protease,study the culture conditions of enzyme production of target strains,and apply them to Daqu to improve the quality of baijiu.The main findings are as follows:(1)Aspergillus A with high glucoamylase yield was obtained by screening.Through experiments,it could be found that the most suitable carbon source of Aspergillus A was sorghum powder,and the best nitrogen source was peptone.The optimum culture temperature was 31℃,culture time was 75 h,pH value was 5.0,inoculation amount was6%,and glucoamylase activity was 210 U/mL.When the initial pH value was 3,the activity of glucoamylase could still reach 63.39% of the maximum value,and it had strong acid resistance.The glucoamylase activity of Aspergillus A strain was dependent on the environment with low alcohol concentration,and the strain had high alcohol tolerance.Through molecular biological identification and physiological and biochemical analysis,it was found that the strain was Aspergillus niger.(2)Aspergillus C with high acid protease production was obtained by screening.It could be observed that the most suitable carbon source of Aspergillus C was bran,and the best nitrogen source was peptone.The optimum culture temperature was 38℃,culture time was 73 h,pH value was 4.0,inoculation amount was 6%,and acid protease activity was 358 U/mL.When the initial pH value was 2.5,the activity of acid protease could still reach 64.43% of the maximum value,and it had strong acid resistance.When the alcohol content was 15% vol,the activity of acid protease produced by the strain was about 56.92%of the peak value,and it had strong tolerance to alcohol.Through molecular biological identification and physiological and biochemical analysis,it could be concluded that the strain was Aspergillus oryzae.(3)Aspergillus B with high esterification enzyme yield was acquired by screening.According to the results of experiments,the most suitable carbon source of Aspergillus B was corn flour and the most suitable nitrogen source was soybean flour.The optimum culture temperature was 34℃,culture time was 99 h,pH was 6.0,inoculum amount was8%,and the esterification ability was 214 U/g.When the initial pH value was 4,the esterification ability could still reach 82% of the peak value,and it had strong acid resistance.The optimum initial alcohol concentration ranged from 0% vol to 6% vol.Through molecular biological identification and physiological and biochemical analysis,it was determined that the strain was Monascus.(4)The functional koji samples were prepared by three selected functional strains,and then mixed functional koji samples were prepared according to the proportion.Furthermore,Box-Behnken response surface was used to optimize the addition amount of functional koji samples.The optimum combination was 16.93% of glucoamylase,6.34%of acid protease and 12.70% of esterification enzyme.Besides,the total ester content reached the theoretical peak of 287.393 mg/100 mL.The theoretical data were verified,and the addition amount of each functional koji sample was set to the best combination,and the solid-state simulated fermentation experiment was carried out three times.The average total ester content was 292 mg/100 mL,which was close to the predicted value.(5)The fermentation process of nongxiangxing baijiu in industrial production was simulated.The experimental group strengthened the specific functional strains in the fermentation environment by mixing functional koji samples,and monitored the physical and chemical indexes of fermented grains in the fermentation process.According to the research results,the addition of mixed functional koji was conductive to improving the saccharification ability of raw materials and the formation of flavor substances,and promoting the quality of baijiu.