Bioconversion of hemicellulosic hydrolysates into ethanol with the desired yields plays a pivotal role for the overall success of biorefineries. This paper aims to evaluate the ethanol production potential of four native strains of Scheffersomyces shehatae (syn. Candida shehatae) viz. S. shehatae BR6-2AI, CG8-8BY, PT1-1BASP and BR6-2AY, isolated from Brazilian forests. These strains were grown in commercial d-xylose-supplemented synthetic medium and sugarcane bagasse hemicellulose hydrolysate. S. shehatae BR6-2AY showed maximum ethanol production [0.48 ± 0.019 g g−1, 95 ± 3.78 % fermentation efficiency (FE)] followed by S. shehatae CG8-8BY (0.47 ± 0.016 g g−1, 93 ± 3.12 % FE), S. shehatae BR6-2AI (0.45 ± 0.01 g g−1, 89 ± 1.71 % FE) and S. shehatae PT1-1BASP (0.44 ± 0.02 g g−1, 86 ± 3.37 % FE) when grown in synthetic medium. During the fermentation of hemicellulose hydrolysates, S. shehatae CG8-8BY and S. shehatae BR6-2AY showed ethanol production (0.30 ± 0.05 g g−1, 58 ± 0.02 % FE) and (0.21 ± 0.01 g g−1, 40 ± 1.93 % FE), respectively.

Many toxic compounds are produced and released in the hemicellulosic hydrolyzates during the acid pretreatment step, which are required for the disruption of the lignocelluloses matrix and sugars release. The conventional methods of detoxification i.e. overliming, activated charcoal, ion exchange or even membrane-based separations have the limitations in removal of these toxic inhibitors in fermentation process. Hence, it is imperative to explore biological methods to overcome the inhibitors by minimizing the filtration steps, sugar loss and chemical additions. In the present study we screened sixty-four strains of yeasts to select potential strains for detoxification of furfural, acetic acid, ferulic acid, 5-hydroxymethyl furfural (5-HMF) as carbon and energy source. Among these strains Pichia occidentalis M1, Y1 0 a, Y1 0 b and Y3 0 showed a significant decrease in the toxic compounds but we selected two best yeast strains i.e. P. occidentalis Y1 0 a and P. occidentalis M1 for the further experiments with an aim to remove the fermentation inhibitors. The yeasts P. occidentalis Y1 0 a and P. occidentalis M1 were grown aerobically in sugarcane bagasse hemicellulose hydrolysate under submerged cultivation. For each yeast, a 2 2 full factorial design was performed considering the variables-pH (4.0 or 5.0) and agitation rate (100 or 300 rpm), and the percentage removal of HMF, furfural, acetic acid and phenols from hemicellulosic hydrolysates were responsive variables. After 96 h of biological treatment, P. occidentalis M1 and P. occidentalis Y1 0 a showed 42.89 and 46.04 % cumulative removal of inhibitors, respectively.