Biological detoxification of the hemicellulosic hydrolyzates of sugarcane bagasse for using in fermentative processes

Durante a etapa de pre-tratamento acido, necessaria para o rompimento da matriz lignocelulosica e liberacao de acucares, diversos compostos toxicos sao formados e liberados no hidrolisado hemicelulosico. Estes compostos afetam negativamente o processo de fermentacao, sendo necessaria uma etapa de destoxificacao do hidrolisado hemicelulosico. Este trabalho teve como objetivo contribuir para o desenvolvimento de um metodo de destoxificacao biologica do hidrolisado hemicelulosico. Com este proposito foram selecionadas leveduras, em meio de cultura sintetico, capazes de utilizar furfural, 5- hidroximetilfurfural (HMF), acido acetico, acido ferulico e siringaldeido como fontes de carbono e energia. As leveduras Issatchenkia occidentalis M1 e Issatchenkia occidentalis Y1\'a foram as que demonstraram os melhores resultados de remocao destes compostos em meio de cultura sintetico e consequentemente foram as selecionadas para os experimentos que foram realizados em hidrolisado hemicelulosico de bagaco de cana-de-acucar concentrado. Em um segundo momento, foi verificado a eficiencia na destoxificacao biologica do hidrolisado hemicelulosico para futuras aplicacoes em processos fermentativos de producao de etanol. Para cada levedura selecionada foi realizado um planejamento fatorial completo 22, com tres repeticoes no ponto central. As variaveis, pH (4,0 ou 5,0) e agitacao do sistema (100 rpm ou 300 rpm), foram avaliados e como variavel resposta foi considerada a porcentagem da remocao de HMF, furfural, acido acetico e fenois do hidrolisado hemicelulosico apos 96 horas de tratamento biologico. A partir dos resultados obtidos constatou-se que para a estirpe de Issatchenkia occidentalis M1 o experimento 4 (pH 5,0 e 300 rpm) foi o que possibilitou uma remocao mais eficiente de cerca de 42,89% dos compostos toxicos totais, sendo 94,77% de HMF 99,19% de furfural, 29,17% de fenois e 100% de acido acetico. Para a estirpe de Issatchenkia occidentalis Y1\'a o experimento 3 (pH 4,0 e 300rpm) foi o que permitiu uma remocao mais significatica de cerca de 46,04% dos compostos toxicos totais, sendo 97,68% de HMF, 96,06% de furfural, 27,15% de fenois e 100% de acido acetico. Os resultados obtidos neste trabalho demonstram o potencial das leveduras Issatchenkia occidentalis M1 e Issatchenkia occidentalis Y1\'a no tratamento biologico do hidrolisado hemicelulosico para a remocao de compostos toxicos liberados pela etapa de pre-tratamento acido.During the acid pretreatment step, required for the disruption of the lignocelluloses matrix and sugars release, several toxic compounds are produced and released in the hemicellulosic hydrolyzates. These compounds negatively affects the fermentation process, being necessary an additional step for detoxification of the hemicellulosic hydrolysates. The present work aimed to contribute for the development of a biological detoxification method of the hemicellulosic hydrolysates. For this purpose yeasts were selected, in synthetic culture medium, capable to metabolize furfural, 5- hydroxymethylfurfural (HMF), acetic acid, ferulic acid and syringaldehyde as carbon and energy sources. The yeasts Issatchenkia occidentalis M1 and Issatchenkia occidentalis Y1\'a demonstrated the best results to remove these compounds present in medium and they were selected to the experiments that had been carried through in concentrated sugarcane bagasse hemicellulosic hydrolyzates. In a second moment, the efficiency of the biological detoxification of the hemicellulosic hydrolyzates was verified for future applications in fermentative processes for ethanol production. For each selected yeast, a 22 full factorial design was carried out. The variables, pH (4.0 or 5.0) and agitation rate (100 rpm or 300 rpm), had been evaluated and as response variable was considered the percentage of HMF, furfural, acetic acid and phenols removed from hemicellulosic hydrolyzates after 96 hours of biological treatment. According with the results, was evidenced that Issatchenkia occidentalis M1 strain, in the experiment conditions 4 (pH 5.0 and 300 rpm), was more efficient removals (about 42.89% of total toxic composites), being 94.77% of HMF, 99.19% of furfural, 29.17% of phenols and 100% of acetic acid. For the Issatchenkia occidentalis Y1\'a strain, in the experiment conditions 3 (pH 4.0 and 300 rpm) was observed significant removal (about 46.04% of total toxic composites), being 97.68% of HMF, 96.06% of furfural, 27.15% of phenols and 100% of acetic acid. The results demonstrate the potential of the yeasts Issatchenkia occidentalis M1 and Issatchenkia occidentalis Y1\'a in the biological detoxification of the sugarcane bagasse hemicellulosic hydrolyzates for removing the toxic compounds released during the acid pretreatment step