Enzymatic hydrolysis of corncob and ethanol production from cellulosic hydrolysate

Enzymatic hydrolysis of corncob and ethanol fermentation from cellulosic hydrolysate were investigated. After corncob was pretreated by 1% H2SO4 at 108 °C for 3 h, the cellulosic residue was hydrolyzed by cellulase from Trichoderma reesei ZU-02 and the hydrolysis yield was 67.5%. Poor cellobiase activity in T. reesei cellulase restricted the conversion of cellobiose to glucose, and the accumulation of cellobiose caused severe feedback inhibition to the activities of β-1,4-endoglucanase and β-1,4-exoglucanase in cellulase system. Supplementing cellobiase from Aspergillus niger ZU-07 greatly reduced the inhibitory effect caused by cellobiose, and the hydrolysis yield was improved to 83.9% with enhanced cellobiase activity of 6.5 CBU g−1 substrate. Fed-batch hydrolysis process was started with a batch hydrolysis containing 100 g l−1 substrate, with cellulosic residue added at 6 and 12 h twice to get a final substrate concentration of 200 g l−1. After 60 h of reaction, the reducing sugar concentration reached 116.3 g l−1 with a hydrolysis yield of 79.5%. Further fermentation of cellulosic hydrolysate containing 95.3 g l−1 glucose was performed using Saccharomyces cerevisiae 316, and 45.7 g l−1 ethanol was obtained within 18 h. The research results are meaningful in fuel ethanol production from agricultural residue instead of grain starch.