Cassava Pulp Enzymatic Hydrolysate as a Promising Feedstock for Ethanol Production

Abstract

The aim of this study was to produce bioethanol from enzymatic hydrolysates of cassava pulp, a by-product of cassava flour manufacturing, using an alcohol-tolerant Saccharomyces cerevisiae strain. First, the best operational condition of the starch hydrolysis process was determined through a complete factorial design (24), with triplicates at the central point. The independent variables evaluated were: the concentrations of α-amylase (Termamyl 2X) and glucoamylase (AMG 300L) and both liquefaction and saccharification times. The most favorable hydrolysis condition in the assay was achieved using 0.517 mL AMG.g starch-1 and 0.270 mL Termamyl.g starch-1, with liquefaction and saccharification times of 1 and 2 h, respectively. The broth obtained at this hydrolysis condition contained a high glucose concentration (160 g.L-1). Once the best reaction conditions were determined, fermentation tests were carried out in a 3 L bioreactor, in a batch system, at 30 °C, 100 rpm and pH 5.5, using 3 g.L-1 (dry biomass) of yeast as inoculum. After 24 h of fermentation, an ethanol concentration of 68 g.L-1 was obtained, with 0.48 ethanol yield and 2.83 g.L-1.h-1 productivity. These results indicate the potential use of cassava pulp, a by-product of cassava flour industries in Brazil, as a raw material for bioethanol production.