Enzymatic Hydrolysis and Fermentation of Pretreated Cashew Apple Bagasse with Alkali and Diluted Sulfuric Acid for Bioethanol Production

Abstract

The aim of this work was to optimize the enzymatic hydrolysis of the cellulose fraction of cashew apple bagasse (CAB) after diluted acid (CAB-H) and alkali pretreatment (CAB-OH), and to evaluate its fermentation to ethanol using Saccharomyces cerevisiae. Glucose conversion of 82 ± 2 mg/g CAB-H and 730 ± 20 mg/g CAB-OH was obtained when 2% (w/v) of solid and 30 FPU/g bagasse was used during hydrolysis at 45 °C, 2-fold higher than when using 15 FPU/g bagasse, 44 ± 2 mg/g CAB-H, and 450 ± 50 mg/g CAB-OH, respectively. Ethanol concentration and productivity, achieved after 6 h of fermentation, were 20.0 ± 0.2 g L⁻¹ and 3.33 g L⁻¹ h⁻¹, respectively, when using CAB-OH hydrolyzate (initial glucose concentration of 52.4 g L⁻¹). For CAB-H hydrolyzate (initial glucose concentration of 17.4 g L⁻¹), ethanol concentration and productivity were 8.2 ± 0.1 g L⁻¹ and 2.7 g L⁻¹ h⁻¹ in 3 h, respectively. Hydrolyzates fermentation resulted in an ethanol yield of 0.38 and 0.47 g/g glucose with pretreated CAB-OH and CAB-H, respectively. Ethanol concentration and productivity, obtained using CAB-OH hydrolyzate, were close to the values obtained in the conventional ethanol fermentation of cashew apple juice or sugar cane juice.