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.

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 5.8S and 26S 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. Y P/S values for the production of ethanol ranging between 0.29 and 0.35 g g -1 were observed under non-optimized conditions.

RESUMO -Estudos voltados para o desenvolvimento de processos biotecnológicos que utilizam biomassas residuais vêm sendo amplamente estimulados nos últimos anos. Neste contexto, o presente trabalho teve como objetivo otimizar o processo de produção de xilanase em fermentação submersa utilizando uma linhagem de Aspergillus tubingensis e torta de algodão como fonte de carbono. A otimização da produção da enzima acima foi realizada por aplicação de uma metodologia de superfície resposta. O extrato enzimático foi caracterizado quanto aos parâmetros de temperatura e pH ótimos, bem como sua estabilidade frente a essas variáveis . A condição ideal para a produção de xilanase foi de 1,25% de torta de algodão num meio líquido contendo 0,9 g/L de NH 4 NO 3 , após 101 horas de fermentação, a qual exibiu valores de 42 U/mL de atividade xilanolítica. No que diz respeito à caracterização bioquímica da atividade xilanolítica foi possível observar uma temperatura ótima de 55 ° C e pH ótimo próximo de 4,0, condição a qual a atividade xilanolítica observada foi de 76,4 U/mL.

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