Evaluation of the production capacity of bioethanol from sugarcane bagasse hydrolysates by different industrial strains of S. cerevisiae

Abstract

In Brazil, bioethanol is derived from the fermentation broth of sugarcane or molasses, being named first-generation bioethanol. Although this process is well established, increasing its efficiency remains a constant learning and new challenges present themselves to the use of bagasse as a feedstock in the second generation process (cellulosic ethanol). The selection of a strain, stress tolerance to traditional industrial and inhibitors present in hydrolysates of sugarcane bagasse, may have application in ethanol plants already established in the country, where hydrolysates are used along with molasses within technology current fermentation of hexoses. On the face of it, this study aims to evaluate the ability of bioethanol production by different industrial strains of S. cerevisiae, from the acid, alkaline and enzymatic hydrolysis of sugarcane bagasse. The kinetic parameters will be evaluated are: umáx (maximum specific growth rate), Yx/s (biomass yield on substrat ) and Yp/s (product yield on substrate). Also the efficiency of fermentation will be determined by the relationship between Yp/s and the maximum theoretical yield. The fermentations will be carried out in shake flasks under anaerobic conditions at a constant temperature of 30ºC , pH 5.0 and 100 rpm agitation , employing different hydrolysates of bagasse sugarcane (acid, alkaline and enzymatic) as substrate. The sampling will be performed at predetermined periods: 0, 6, 12, 24, 36 and 48 hours of fermentation. The samples will be centrifuged and the concentration of biomass will be determined by gravimetric analysis of dry mass. In the supernatant will be quantified concentrations of reducing sugars (RS), total reducing sugars (TRS) by the method of DNS (3,5- dinitrosalicílico acid) and also the glucose concentration by the enzyme glucose oxidase -peroxidase method (GOD-POD). Besides the sugar concentration will be also determined in the supernatant the ethanol concentration by gas chromatography. Finally, after the end of fermentation will be determine the cell viability of S. cerevisiae strains studied.