Abstract
Considered as a promising alternative energy source, agro-industrial biomass needs a pre-treatment step for conversion to sugars, which can release not only hexoses but also pentoses and other sugars, as well as inhibitors. The inhibitory effect of acetic acid, furfural and hydroxymethylfurfural in ethanol kinetics production from Pichia stipitis yeast, in the presence of commercial glucose and xylose and Yeast Nitrogen Base (YNB) is investigated in this work. Fermentations took place in 250 mL Erlenmeyer flasks, at room temperature, 150rpm and 72 h without pH control, with an initial concentration of 109 cells/mL. The mixture of the inhibitorsnegatively influence the process, not observing cell growth, and about 95% of non-viable cells at 48 h of fermentation, despite the consumption of 40% glucose and 35% xylose. In comparison with the control test (without addition of inhibitors), the isolated use of 0.05 g/L hydroxymethylfurfural and 0.25 g/L furfural presented profile slightly lower, with almost complete conversion of xylose and 60% glucose to ethanol, reaching ethanol yield around 40%. Isolated addition of 1.75 g/L acetic acid significantly influenced the process, leading to yield less than 5% and 80% of non-viable cells at 48 h, indicating that this is the main inhibitor of ethanol production.
