Abstract
The conversion of pentoses into ethanol remains a challenge and could increase the supply of second-generation biofuels. This study sought to isolate naturally occurring yeasts from plant biomass and determine their capabilities for transforming xylose into ethanol. Three yeast strains with the ability to ferment xylose were isolated from pepper, tomato and sugarcane bagasse. The strains selected were characterized by morphological and auxanographic assays, and they were identified by homology analysis of 5.8 S and 26 S ribosomal RNA gene sequences. The identities of two lineages of microrganism were associated with Galactomyces geotrichum, and the other was associated with Candida akabanensis. Fermentative processes were conducted with liquid media containing only xylose as the carbon source. YP/S values for the production of ethanol ranging between 0.29 and 0.35 g g−1 were observed under non-optimized conditions.
Highlights
The lignocellulosic biomass is considered to be the most accessible and abundant renewable raw material existing on the planet (Zhou et al, 2011)
The carbohydrates present in plant cell walls could be transformed into ethanol by a technological route that consists of pretreatment of the lignocellulosic material, hydrolysis of polysaccharides and conversion of the sugars released into alcohol by a fermentative process (Talebnia, Karakashev & Angelidaki, 2010; Bhatia, Johri & Ahmad, 2012)
Both the 26S rDNA regions amplified from the UFVJM-R10 and UFVJM-R150 strains and the 5.8S rDNA regions amplified from the UFVJM-R150 strain presented a probable identity with those of the Galactomyces geotrichum and Geotrichum candidum species when search with BLAST (Table 5)
Summary
The lignocellulosic biomass is considered to be the most accessible and abundant renewable raw material existing on the planet (Zhou et al, 2011). The hemicelluloses comprise the other polysaccharidic fraction, representing 28.5–37.2% of the plant cell wall (Pauly & Keegstra, 2008). The carbohydrates present in plant cell walls could be transformed into ethanol by a technological route that consists of pretreatment of the lignocellulosic material, hydrolysis of polysaccharides and conversion of the sugars released into alcohol by a fermentative process (Talebnia, Karakashev & Angelidaki, 2010; Bhatia, Johri & Ahmad, 2012). Xylose and other pentoses released after the pretreatment of lignocellulosic material are frequently discarded because the microorganisms conventionally used in industry have no capacity to ferment pentoses (Gírio et al, 2010; Claassen et al, 1999). The conversion of the hemicellulose fraction from the lignocellulosic biomass into ethanol could represent an increase of 50% in the production of second-generation ethanol (Nogué & Karhumaa, 2015)
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