Abstract: Two tannin-tolerance mutant strains P05 and P18 were obtained by UV irradiation, tannin gradient domestication and screening with Pachysolen tannophilus 1770 as the starting strain and the ethanol yield rate as screening factor. The tannin and ethanol tolerances of P18 and the original strain P. tannophilus 1770 were studied. The fermentation of acorn starch for ethanol production were also compared. The results showed that the genetic characters of P05 and P18 were stable. After generation through five passages, the ethanol concentrations in the fermentation liquid of P05 and P18 with 70 g/L acorn starch reached 71.30 and 77.07 g/L, and increased by 13.95% and 23.17% than that of P.tannophilus 1770, respectively. Compared with P.tannophilus 1770, P18 had better tannin tolerance and ethanol tolerance, the biomass of P18 increased 53.33% in the medium of 2.00% tannin, and increased 43.48% in the medium of 2.50% tannin. On the other hand, the ethanol tolerance of P18 increased 8.82% with the medium of 2.00% ethanol. By using P18, the extraction process in fermentation could decrease from 5 to 3 times. This simplify the production process and reduce the ethanol production cost. The optimal fermentation conditions of the acorn starch extracted for 3 times using P18 were determined as temperature 30 ℃, the pH value 5.5, and the inoculation quantity 6.0%-8.0%. The ethanol concentration in the fermentation liquid reached 85.18 g/L under these conditions, and the ethanol yield reached 0.37 g/g.

Key words: Pachysolen tannophilus, tannin-tolerance, UV irradiation, domestication