Research On Nutritional Flavor Substances Of Green Tea Craft Beer And Utilization Of Yeast Slurry

China is a big producer of beer.Although the total amount is huge,there are still many deficiencies in individuation and specialty.With the increasing consumption demand of Chinese people,the demand for characteristic flavored beer is becoming increasingly strong.At the same time,how to utilize the byproduct yeast of beer brewing industry in high value is also a hot issue to be solved.Green tea is widely grown in many places in China and is loved by people for its unique flavor and health benefits.In this paper,green tea is applied to beer brewing,and a strain of saccharomyces cerevisiae with excellent performance is selected,combined with the optimization of brewing process,to brew a unique flavor of green tea craft beer,and its nutritional value is further studied.At the same time,the yeast mud produced by brewing was broken and applied to the synthesis of Polysialic acid(PSA).The main research contents are as follows:(1)In this chapter,S.cerevisiae BKS-03 was used as the starting strain for UV and ARTP complex mutagination,and S.cerevisiae QLJJ72 with excellent characters was obtained.S.cerevisiae QLJJ72,S.cerevisiae BKS-03 and four strains of(S.cerevisiae S189,S.cerevisiae BE-134,S.cerevisiae K-97,S.cerevisiae W34/70)for comparison of biological characteristics and fermentation indices.The results showed that S.cerevisiae QLJJ72 obtained by mutagenesis was a good choice for brewing green tea beer..(2)Based on S.cerevisiae QLJJ72 obtained by screening,the appropriate brewing process of green tea beer was explored.In this chapter,single factor experiment was used to investigate the effects of raw wort concentration,tea amount,fermentation temperature and yeast inoculation amount on the sensory effects of green tea beer.On this basis,response surface method was used to optimize the brewing process of green tea beer.The fermentation parameters of green tea beer were determined as follows: tea dosage 3.17g/L,yeast inoculation amount 9%,fermentation temperature 22.32℃.Under these conditions,the sensory score predicted by the model was 93.2284 points.The physical and chemical indexes of green tea beer brewed with this fermentation parameter are as follows: Diacetyl 0.0864 mg/L,total acid 1.68 m L / 100 m L,alcohol content 3.9%vo L,original wort concentration 11 °P,carbon dioxide 0.67%,color 11.68 EBC,bitterness 9.37 IBU,pH 4.15,bubble retention 270 s,fermentability 66.89%,It is a high quality beer in line with national standards.(3)Compared and analyzed the difference of nutrition and flavor substances,antioxidant strength and sensory evaluation between the finished green tea beer brewed by the above process and the three beers purchased on the market.In this chapter,the nutrients and flavor substances in the four kinds of beer were determined.The results showed that the green tea beer brewed in this study was more diversified in nutrients,and contained more minerals and amino acids than other green tea beers.Compared with German wheat beer,green tea beer contains more flavor substances,including tea spirane and nerolol,etc.During beer storage,green tea beer shows stronger antioxidant power in the changes of total phenols and antioxidant indexes,which can make the beer has higher biological stability.In terms of sensory evaluation of the four kinds of beer,the green tea beer brewed in this experiment scored better in all aspects.(4)The brewed yeast mud is subjected to wall breaking treatment.Based on its cytidine triphosphate(CTP)regeneration ability,it can be used for PSA synthesis to realize high value utilization of beer yeast mud.In this chapter,the freeze-thaw wall breaking parameters of brewer’s yeast mud were studied,and the optimized freeze-thaw wall breaking parameters were obtained as follows: adding 20% water and freeze-thaw 4times,and the yeast wall breaking rate was 45.58%.The appropriate reaction conditions for CTP conversion were explored,and the high conversion conditions were cytidine monophosphate(CMP)30 mmol/L,glucose 150 mmol/L,phosphate 250 mmol/L,yeast0.3 g/m L,and conversion time 80 min.Under these conditions,the conversion rate of CTP can be as high as 59.11%.When applied to PSA synthesis,the yield of PSA increased from 0.361 g/L to 0.425 g/L after adding yeast mud.