Influence of inhibitors compounds on ethanol production by Scheffersomyces stipitis ATCC 58376

The hydrolysis of lignocellulosic biomass, in particular acid hydrolysis, generates toxic compounds that affect microbial growth and ethanol production. In order to know the effects of the major inhibitors present in hemicellulose hydrolysates on the metabolism of Scheffersomyces stipitis ATCC 58376, this yeast was grown in synthetic medium (g/L: xylose 40, glucose 5.0, peptone 6.0, yeast extract 3.0 and malt extract 3.0) with different concentrations of the inhibitors furfural, HMF, acetic acid, vanillin and syringic acid, according to a factorial design Plackett and Burman, at 30°C, 200 rpm, for 96 hours. Among the factors evaluated for the response cell growth, only acetic acid was significant (at the 10% level) at 72 and 96 hours. The acetic acid effect was negative (-2.445 and -2.728) at 72 and 96 hours, respectively. This result indicates that for the concentrations of acetic acid evaluated (2.0, 4.0 and 6.0 gL/), the degree of inhibition of cell growth was more severe than the other compounds tested. Regarding the response ethanol production, among the factors evaluated, only the effect of furfural was not significant. Acetic acid and HMF had negative effects, whereas vanillin and syringic acid promoted a positive effect on ethanol production. The maximal ethanol concentration (14 g/L) was observed in the test 9 (g/L: furfural 0.025, HMF 0.01, acetic acid 2.0, vanillin 0.90 and syringic acid 0.75) after 72 hours. In the tests with 6 g/L acetic acid, the yeast metabolism of was completely inhibited.