Breeding Of Saccharomyces Cerevisiae Strain Of Cassava Alcohol Fermentation,Pilot And Industrial Test

Fuel alcohol from cassava is currently the only true sense non-food biofuel alcohol in our country. However, the raw material prices for alcohol production have been soaring for competing with the cassava starch products and most alcohol production enterprises in Guangxi province have experienced the pain of downtime to be produced stage. So the primary task for them is to seek low-cost fermentation technology and processes. The high alcohol-producting, low reducing sugar and fast fermentation Saccharomyces cerevisiae strain with its fermentation process can meet the demand to reduce the raw material, overall production and operating costs and maintain normal production enterprises.In this study,200 samples were collected from different environments which contain high sugar such as sugar factories, farms and sales sites of sugar. The samples were put into 10%（V/V） alcohol in natural storage 60 d to eliminate the strains with low Alcohol tolerance in initially. After rescreening by propagation and fermentation characteristics, two strains were got which can rapid produce high concentration of alcohol with low residual sugars. The results of fermentation experiments showed that the two strains could achieve higher concentration of alcohol with low residual sugars in 48 h.However, the residual sugars of the two wild strains are still high for industrial production. To obtain low residual sugars and high alcohol-producing mutants, the two strains protoplast were treated by UltraViolet （UV）-nitrosoguanidine （NTG） composite mutation,⁶⁰Co mutagenesis, respectively. The experiments results showed that UV-NTG composite mutation was better than ⁶⁰Co mutagenic. A mutant strain was obtained through primary screening and confirmed screening. The final alcohol concentration of the strain could reach to 16.39%（V/V） with the fermentation temperature at 37℃ and the residual sugars were reduce. The strain could remain steady the traits of fast growth and fermentation, low residual sugars through many times subculture.The mutant strain was tested five batches fermentation in 50 L fermentor and three batches fermentation in 500 L fermentor. The average final alcohol concentration of 50 L fermentor could reach to 16.7 %（V/V） in 48 h under the simulaged fermentation conditions of alcohol production. The fermentation time was reduced by 20% than Faerkai active dry yeast with fermentation 60 h. The average final alcohol concentration of 500 L fermentor could reach to 14.98%（V/V） in 40 h with the residual sugars 0.72 g/100 mL. These results showed that the strain could meet the requirements for alcohol large-scale production.The mutant strain was also tested three batches fermentation in 100,000 t fermentor of Guangxi Xintiande energy company. The fermentation crafts and conditions were the same in the situation of the company and the fermentation pattern was used in semi-continuous fermentation. The results showed that the indicators of yeast gradually stabilized with the yeast number of 2.45×108/mL and budding rate of 17.48%. The final alcohol concentration could reach to 14.7%（V/V） in 52 h in 200 m3 single fermentation tank, with the residual reducing sugars of 0.69%（g/100 mL） and the residual total sugars of 1.46%（g/100 mL）.In order to facilitate evaluation the excellent characteristics of the tested strains, the fermentation assessment indicators of companies were amended and the fermentation efficiency as the main assessment indicators were presented in this paper. The fermentation assessment indicator not only provides the technical references for alcohol production enterprise, but also provides an opportunity for the promotion of good strains.