Breeding Of High-yield Alcohol-producing Yeast And Fermentation Process Condition Optimization

Biomass is the most abundant renewable resource in nature, there are many kinds of biomass energy in our country. Cassava is one of the most ideal biomass energy crops and known as "King of starch". After liquefaction and treatment, there is rich in sugar and cassava can be used by microorganisms. Using cassava as raw material to produce fuel ethanol can not only ease the energy and food crisis, but also reduce costs and improve the ecological environment. In order to realize the economic feasibility of biomass fuel ethanol production, the breeding of saccharomyces cerevisiae has become a hot research topic. Thus, it is great of significance to improve the fermentation efficiency and reduce the production cost of biomass fuel ethanol via breeding of Saccharomyces cerevisiae with high yield and other good traits.In this study, we take the industrial brewing yeast NY-1308 as the original strain. After drawing growth curve of strain NY-1308, the original strain during logarithmic phase was chose to carry out the plasma mutagenesis of ARTP. We finally obtained a stable and high yield mutant yeast strain S-12 after TTC screening and shake flask screening. Mutant strains were fermented in the fermentation medium. At the end of fermentation, liquor can reach to be 17.5%, and ethanol production increased by 12.9% compared with the wild strain. The results showed that the mutant strain had the potential to produce fuel ethanol in the industrial production.In order to further improve the fermentation capacity of the mutant strain S-12 and achieve the production of biomass fuel ethanol with high efficiency, we carried out the experiments to optimize the fermentation conditions using single factor and orthogonal test analysis methods. Optimal fermentation process was as follows:Optimal fermentation temperature was 33?, initial pH 5.0, inoculum concentration 20%(V/V), Urea 0.7g/100g, Mg2SO4 0.6g/100g, KH2PO4 1.0g/100g, CaCl2 0.9g/100g, diastatic enzyme 240U/g, four times average addition 0-24h. At the end of fermentation, liquor can reach 18.2%, the starch utilization rate reached more than 92%.In order to realize industrial production, we also used 50 L fully automatic fermentation tank, carried out the simultaneous fermentation test for the strain S-12. We established the optimal fermentation conditions in technological level:Ventilation time 12 h, Ventilation rate 3-5 L/min; Before 12h stirring rate of 300 rpm, Stirring rate of 140 rpm in the fermentation stage, The adding amount of the enzyme was 180 U/g, four times average addition 0-24 h. Finally, the alcohol content reached 18.4% vol,18.7% higher than the original strain in 50 L automatic fermentation tank.