Screening Of Alcohol Yeasts With High Thermotolerance And The Fermentation Process Optimization

The initial yeast strain of alcohol FY-23, which was afforded by stain conservation centre of BBCA Group, was mutated by exposing the protoplasm in the ultraviolet radiation. Then by scanning and purification, a new strain that had high temperature tolerance was obtained.We started our research from the physiological traits, including the conditions of the highest forming and regeneration percentage, such as pre-culture time, concentration of the enzyme and its processing time. The result is, using 1.5% Snailase, to hydrolyse for 25min, the forming percentage of protoplasm and regeneration ratio could be up to 99.54% and 5.1% respectively. Also we studied the fatal curve of protoplasm by exposuring them in the ultraviolet radiation. According to the curve, the plates for regeneration which was illumined for 10, 15 and 20 seconds were selected as candidates for the next TCC tests.After the TCC tests, we got 9 positive colonies whose colors were deeper than any others. After the second round selection in Durham and flask, the strain FY-23-9, which showed better performance in different aspects than other strains, was used to fermentate, in order to discuss the optimum conditions, such as DE value of liquefaction of corn starch, DE value of DE value of saccharification solution, ratio of stock/water, temperature, initial pH and inoculation volume. Some of the conditions were tested by orthogonal method, and the optimum result is, ratio of stock to water, 1:2; DE value of liquefaction, 20%; DE value of saccharification solution, upper than 95%; temperature, 30℃; initial pH, 5.0 and the inoculation volume, 10%. At last, experiments were taken on the 50L full automatic fermenter in order to validate these conditions. 72 hours later, the concentration of the alcohol could be up to 11% (v/v), residual sugar could be decreased to 0.47%, and conversion was 43.21%. This is almost the same as the wild strain FY-23 being. We consider that the optimum strain FY-23-9 could be used in the industrialized scale.