Screening and identification of an aroma-producing yeast and optimization of fermentation conditions for ester production

In this study, a superior aroma-producing yeast was isolated and screened from distillers' grains, Jiuqu, grape, persimmon, fermented grains and sauerkraut samples by traditional culture and separation method, smelling method and total ester yield determination, identified by morphological observation, physiological and biochemical tests and molecular biology techniques, and its tolerance was studied. Using total ester content as response value, the fermentation conditions of the screened strains were optimized by single factor tests and response surface tests. The results showed that a total of 64 yeast strains were isolated and purified, and a strain of yeast S1 with superior aroma production property was screened from persimmon samples, which was identified as Pichia kluyveri. The optimal growth temperature of strain S1 was 28 ℃, the optimal growth pH was 6, which could tolerate temperature 40 ℃, pH 2 and 10, ethanol with a volume fraction of 10% and acetic acid of 1.0%. The optimal fermentation conditions of P. kluyveri S1 for ester production were fermentation temperature 32 ℃, inoculum 5%, and fermentation time 5 d, and the total ester content was 1.69 g/L under these optimal conditions, which was 14.19% higher than that before optimization.