Avaliação do hidrolisado hemicelulósico de sabugo de milho suplementado com proteína de farelo de soja solubilizada para a abtenção de bioetanol

Abstract

LOPES, M.M; Evaluation of corn cob hemicelullosic hydrolysate supplemented with soluble soybean meal protein for obtainment of bio-ethanol. 2015. 106p. Dissertation (Master of science) Escola de Engenharia de Lorena, Universidade de Sao Paulo, Lorena, Sao Paulo, 2015. The corn cob, due to its lignocellulosic structure, can be used as a biomass renewable source for soluble sugars can be converted into high value-added products, such as ethanol and others. Acid hydrolysis is the mostly used method to obtain hemicellulosic hydrolysate from lignocellulosic materials, leading to the obtaining of the xylose sugar at the highest concentration, from their hemicellulosic fraction. The xylose fermenting yeast Scheffersomyces stipitis is among the few organisms that utilize both xylose and glucose regulatory systems and exhibits a transition between the respiratory and fermentative processes. This work aims to contribute to the development of a technology to obtain bioethanol by Scheffersomyces stipitis CBS 6054, from the corn cob hemicellulosic fraction, evaluating the nutritional formulation of the fermentation medium. As an alternative of nitrogen source, it was chosen soybean bran. The corn cob hemicellulosic hydrolysate (HHSM) was obtained by acid hydrolysis, vacuum evaporated and treated by pH variation. Hydrolysate of soybean bran was obtained by enzymatic hydrolysis (Alcalase, 60°C, 100 rpm, 3h). The solubility evaluation of the hydrolysate of soybean bran in HHSM (pH 4.0 to 7.0) was performed by 2 2 full factorial design using response surface methodology (RSM). The supplementation of HHSM with solubilized soybean bran protein associated or not with other nutrients (urea and ammonium sulphate) to obtain bioethanol employed a 2 3 full factorial design using RSM. The fermentation was carried out in Erlenmeyer flasks (125 mL) containing 50mL of medium stirred at 150rpm and 30 °C. The inoculum concentration was 1.5 g/L of cells. The results showed that the acid hydrolysis favored removal of the hemicellulosic fraction (88.05%) with little change in cellulose (10.06%) and lignin (27.07%) compared to the in natura material, providing a hemicellulosic hydrolysate rich in xylose (28.30 g/L) with low concentrations of phenolics compounds and furans. Treatment of HHSM reduced protein content in the vaccum evaporated hydrolysate (74.76%) and original hydrolysate (28.53%). Soybean bran had good quality as shown by the protein solubility of KOH of 82.99 % and by urease index of 0.00. The soybean bran enzymatic hydrolysis produced 50.45% more protein than aqueous soybean bran protein extraction, yielding 45 g/L of solubilized protein. In the determination of protein content by the Lowry method was necessary to take into account the presence of interfering species of the HHSM. The maximum soybean bran protein solubility (9.01 g/L) was obtained maximizing the concentration of hydrolysate of soybean bran (5.0 g /L) in HHSM. In the range studied in this work, the pH did not influence the solubility of soybean bran protein in HHSM. For the response surface methodology, the maximum value for the ethanol yield (0.20 g/g.) can be achieved employing hydrolysate of soybean bran in its upper level (5.0 g/L) and urea (3 g/L) and ammonium sulfate (3 g/L) in their center points. The source of soybean bran protein solubilized in HHSM has potential as an alternative nitrogen source for bioethanol production by Scheffersomyces stipitis.