Study of enzymatic hydrolysis at high-solids loading using deacetylated rice straw and fermentability evaluation of the hydrolysate obtained by Candida guilliermondii

• Grant number: 22/08505-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): November 01, 2022
• Effective date (End): July 31, 2023
• Field of knowledge: Biological Sciences - Microbiology - Applied Microbiology
• Principal Investigator: Ines Conceicao Roberto
• Grantee: Giovanni Henrique Silva
• Host Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil

Abstract

Rice straw is composed mostly of polysaccharides (approximately 70%) with glucose being the main sugar of the cellulosic fraction and xylose of the hemicellulosic fraction. These sugars can be fermented by specific microorganisms, such as Candida guilliermondii, to obtain important products within a biorefinery context, such as ethanol and xylitol. For the production of these bioproducts from lignocellulosic biomass, it is first necessary to convert polysaccharides into fermentable monosaccharides by enzymatic hydrolysis, which can be performed at low-solids loading (between 8% and 15% w/v) and at high-solids loading (greater than 15% w/v). Enzymatic hydrolysis with high-solids loading is desirable due to the higher sugar concentration in the hydrolysate obtained, but the limited amount of water and the fibrous nature of the biomass hinders mass transfer and its saccharification. To circumvent this problem, unconventional reactors with different impeller configurations are developed in order to favor mixing and, consequently, enzymatic hydrolysis. In addition to reactor configuration and solids loading, another important factor in the efficiency of enzymatic hydrolysis is the selection of the appropriate enzyme cocktail for the type and pre-treatment of biomass. Currently, the research group of the Fermentation Laboratory I of the Biotechnology Department of the Engineering School of Lorena, University of São Paulo (EEL/USP), is studying the enzymatic hydrolysis of the cellulosic and hemicellulosic fractions of rice straw conditioned to a mild alkaline deacetylation pretreatment that was developed by the group itself. Despite good cellulose conversion (~85%), the group's experiments demonstrated moderate xylan conversion (~64%). Within this context, the present work proposes to evaluate the effect of xylanase supplementation and the performance of the unconventional reactor with an anchor-type impeller in the enzymatic hydrolysis at high-solids loading of deacetylated rice straw. Additionally, it is proposed to evaluate the fermentative profile of the yeast Candida guilliermondii FTI 20037 using the obtained enzymatic hydrolysate. (AU)