Resumo

The sweet potato [Ipomoea batatas (L) Lam] would an excellent source of biomass for ethanol production, due to its low production cost and hardiness, but is economically unfeasible because high hydrolysis costs are involved in the process. The activities developed in this study aimed to produce enzymes starch by a strain of the Aspergillus niger isolated from Atlantic rainforest, and evaluating the hydrolyses of five sweet potato cultivars using these enzymes. The best conditions for A. niger amylase production, such as carbon source, pH, temperature and kinetics production were analyzed. Also, the effects of temperature, pH, and reaction time on sweet potato hydrolyses were evaluated. The total reducing sugars were quantified by the dinitrosalicylic acid method and glucose released was quantified by glucose kit enzymatic method. A. niger showed excellent levels of amylase production when grown on Vogel liquid medium supplemented with 1% cassava flour, during 5 days, pH 5.0 and 30 °C. The best conditions for sweet potato cultivar UGA 5 hydrolysis, which showed higher levels of productivity, corresponded to 6 hours of reaction, temperature of 60 °C and pH 4.5. In these conditions, were obtained 0.76 g of reducing sugars and 0.53 g of glucose, from 1 g of potato sweet. When these same hydrolysis conditions were evaluated on the other cultivars, the highest rates of saccharification were obtained by cultivar UGA 56, corresponding to 0.80 g of glucose from 1 g of potato sweet. The bioprocess using A. niger as amylase producer was satisfactory, enabling to reach high levels of sugars in the conversion of starch from sweet potatoes. Future application of this process in industrial scale may substantially reduce the saccharification cost, making the sweet potato ethanol production an economically feasible process.