Resumo

Brazil is one of the world’s largest ethanol producers with approximately 24 billion liters in 2012. During the extraction of sugarcane juice from stem, a substantial amount of sugarcane bagasse (SB) is generated every year. SB has shown the potential as a model substrate for second generation (2G) ethanol production. However, pretreatment and bioconversion of sugars into ethanol are the two key steps for the commercialization of second generation ethanol. Dilute acid hydrolysis using H2SO4 seems an ideal pretreatment strategy for SB which mechanistically depolymerizes hemicellulose fraction of cell wall into mixture of sugars in addition to some undesired products which need to eliminate prior to microbial fermentation. Fermentation tests were carried out in 125 mL Erlenmeyer flasks (30°C, 100 rpm for 96 hrs) containing 50 ml of non-detoxified hydrolysate (NDH) and detoxified hydrolysate (DH) by overlimming i.e. increase of pH until 7.0 with calcium oxide and a reduction to 5.0 with phosphoric acid followed by active charcoal treatment (2.5% w/v). Both hydrolysates (pH 5.5) were supplemented with yeast extract (3.0 g/L), malt extract (3.0 g/L), and peptone (5.0 g/L). Batch fermentation was carried out with 0.5 g/L of Candida shehatae UFMG 52.2 cells as an inoculum. The fermentation assay using detoxified hydrolysate showed 100% of sugars bioconversion within 48h. DH hydrolysate showed ethanol yield (Yp/s) of 0.38 g/g and volumetric productivity (Qp of 0.19 g/L.h). On the other hand, NDH did not show ethanol production due to the presence of inhibitors in the hydrolysate. Detoxification of the Sugarcane bagasse hydrolysate demonstrated its importance in the hemicellulosic ethanol production by the xylose-fermenting Candida shehatae UFMG 52.2 under batch cultivation conditions.