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Xylitol is a building block for a variety of chemical commodities, besides being widely used as a sugar substitute in the food and pharmaceutical industries. The aim of this work was to develop a microbial process for xylitol production using sugarcane bagasse hydrolysate as substrate. In this context, 218 non-Saccharomyces yeast strains were screened by growth on steam-exploded sugarcane bagasse hydrolysate containing a high concentration of acetic acid (8.0 g/L). Seven new Candida tropicalis strains were selected and identified, and their ability to produce xylitol on hydrolysate at low pH (4.6) under aerobic conditions was evaluated.The most efficient strain, designated C. tropicalis JA2, was capable of producing xylitol with a yield of 0.47 g/g of consumed xylose. To improve xylitol production by C. tropicalis JA2, a series of experimental procedures were employed to optimize pH and temperature conditions, as well as nutrient source, and initial xylose and inoculum concentrations. C. tropicalis JA2 was able to produce 109.5 g/L of xylitol with a yield of 0.86 g/g of consumed xylose, and with a productivity of 2.81 g·L·h, on sugarcane bagasse hydrolysate containing 8.0 g/L acetic acid and177 g/L xylose, supplemented with 2.0 g/L yeast nitrogen base and 4.0 g/L urea. Thus, it was possible to identify a new C. tropicalis strain and to optimize the xylitol production process using sugarcane bagasse hydrolysate as a substrate. The xylitol yield on biomass hydrolysate containing a high concentration of acetic acidobtained in here is among the best reported in the literature.

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The saccharification of sugarcane bagasse by enzymatic hydrolysis is one of the most promising processes for obtaining fermentable sugar to be used in the production of second-generation ethanol. The objective of this work was to study the immobilization and stabilization of two commercial enzymes: Endocellulase (E-CELBA) in dextran coated iron oxide magnetic nanoparticles activated with aldehyde groups (DIOMNP) and β-glucosidase (E-BGOSPC) in glyoxyl agarose (GLA) so that their immobilized derivatives could be applied in the saccharification of pretreated sugarcane bagasse. This was the first time that the pretreated sugarcane bagasse was saccharified by cascade reaction using a endocellulase immobilized on dextran coated Fe2O3 with aldehyde groups combined with a β-glucosidase immobilized on glyoxyl agarose. Both enzymes were successfully immobilized (more than 60% after reduction with sodium borohydride) and presented higher thermal stability than free enzymes at 60, 70, and 80 °C. The enzymatic hydrolysis of the sugarcane bagasse was carried out with 15 U of each enzyme per gram of bagasse in a solid-liquid ratio of 1:20 for 48 h at 50 °C. Under these conditions, 39.06 ± 1.18% of the cellulose present in the pretreated bagasse was hydrolyzed, producing 14.11 ± 0.47 g/L of reducing sugars (94.54% glucose). In addition, DIOMNP endo-cellulase derivative maintained 61.40 ± 1.17% of its enzymatic activity after seven reuse cycles, and GLA β-glucosidase derivative maintained up to 58.20 ± 1.55% of its enzymatic activity after nine reuse cycles.

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RESUMO -Lipases são enzimas que atuam na interface orgânica aquosa catalisando a hidrólise das ligações éster-carboxilases presentes em acilgliceróis liberando ácidos orgânicos e glicerol, catalisando reações de esterificação, transesterificação ou interesterificação. A obtenção dessas enzimas é um processo caro devido aos altos custos na produção da lipase. Assim, visando diminuir estes custos, este trabalho tem como objetivo estudar a influência da concentração de melaço de soja (co-produto do processo de secagem da proteína de soja) na produção de lipase por Candida e otimizar o tempo de fermentação. Os testes para otimização do tempo de fermentação foram realizados em meio de cultura com pH 6 e concentração de melaço de soja de 200 g/L. A atividade de lipase foi determinada pelo método de titulação com NaOH 0,05N. Os resultados mostram que o melaço de soja é uma boa fonte de nutrientes na produção de lipase. A atividade lipolítica máxima de 5,25 U/mL foi alcançada em 12 horas de fermentação submersa. Após otimizar o tempo de produção, avaliou-se a influência da concentração de melaço de soja no meio para fermentação, obtendo-se os melhores resultados na concentração de 250 g/L.Palavras chave: co-produto, fermentação submersa, influência.