Enzymic saccharification of sugarcane bagasse pretreated by autohydrolysis–steam explosion

Abstract

AbstractPretreatment of bagasse by autohydrolysis at 200°C for 4 min and explosive defibration resulted in the solubilization of 90% of the hemicellulose (a heteroxylan) and in the production of a pulp that was highly susceptible to hydrolysis by cellulases from Trichoderma reesei C‐30 and QM 9414, and by a comercial preparation, Meicelase. Saccharification yields of 50% resulted after 24 h at 50°C (pH 5.0) in enzymic digests containing 10% (w/v) bagasse pulps and 20 filter paper cellulase units (FPU). Saccharifications could be increased to more than 80% at 24 h by the addition of exogenous β‐glucosidase from Aspergillus niger. The crystallinity of cellulose in bagasse remained unchanged following autohydrolysis‐explosion and did not appear to hinder the rate or extent of hydrolysis of cellulose. Autohydrolysis‐exploded pulps extracted with alkali or ethanol to remove lignin resulted in lowere conversions of cellulose (28–36% after 25 h) than unextracted pulps. Alkali extracted pulps arising from autohydrolysis times of more than 10 min at 200°C were less susceptible to enzymic hydrolysis than unextracted pulps and alkali‐extracted pulps arising from short autohydrolysis times (e.g., 2 min at 200°C). Autohydrolysis‐explosion was as effective a pretreatment method as 0.25M NaOH (70°C/2 h) both yielded pulps that resulted in high cellulose conversions with T. reesei cellulase preparations and Meicelase. Supplementation of T. reesei C‐30 cellulose preparations with A. niger β‐glucosidases was effective in promoting the conversion of cellulose into glucose. A ration of FPU to β‐glucosidase of 1:1.25 was the minimum requirement to achieve more than 80% conversion of cellulose into glucose within 24 h. Other factors which influenced the extent of saccharification of autohydrolysis‐exploded bagasse pulps were the enzyme‐substrate ratio, the substrate concentration, and the saccharification mode.