Abstract
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.
Highlights
The demand for alternative and sustainable fuel source has been raised in the last few years due to diminishing petroleum resources, regular price hikes of gasoline and environmental pollution
Xylose (16.0 g l-1) was the main component in hemicellulosic hydrolysate followed by arabinose (1.15 g l-1) and acetic acid (1.05 g l-1)
Canilha et al (2005) observed 18.11 g l-1 of xylose in addition to other by-products (7.6 g glucose l-1 and 2.23 g arabinose l-1). These results show the distinctiveness of the chemical composition of acid hydrolysate due to the difference in hemicellulose composition of each vegetal species and the acid hydrolysis conditions employed (Table 1)
Summary
The demand for alternative and sustainable fuel source has been raised in the last few years due to diminishing petroleum resources, regular price hikes of gasoline and environmental pollution. Ethanol derived from renewable biomass has shown promising results for replacing partially or totally gasoline (Goldemberg 2007). Bioconversion of hemicellulosic sugars into ethanol with satisfactory yields is essential for the total ethanol production from lignocellulosic materials (Saha 2003). Dilute acid hydrolysis leads to the generation of some undesired products such as furfural, 5-hydroxymethylfurfural (HMF), weak acid, extractives and phenolic compounds (Chandel et al 2007; Milessi et al 2012). These compounds are toxic to the microorganisms and are required to be removed from hydrolysates to obtain satisfactory ethanol yields during microbial fermentation (Canilha et al 2013)
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