Evaluation of acids and cellulase enzyme for the effective hydrolysis of agricultural lignocellulosic residues

Abstract

AbstractThis paper reports the results of experimentation carried out to compare the ability of mineral acids (HCl and H2SO4) and cellulase enzyme (from Trichoderma reesei QM 9414) in the saccharification of corn‐cob, groundnut shell, sugarcane bagasse and wheat straw. With the exception of corn‐cobs, acids proved to be better saccharifying agents than the cellulase complex, but the former gave a poor substrate for alcoholic fermentation since the saccharified mashes contained large amounts of pentoses which are not metabolized by most strains of yeast. In addition, both acids and enzymes have been found to be substrate specific. Maximal saccharification of groundnut shell, sugarcane bagasse and wheat straw were obtained with sulphuric acid at 15.0, 5.0 and 5.0% (v/v) under 15, 15 and 15 psi pressure for 15, 30 and 30 min, respectively; whereas hydrochloric acid at 7.5% (v/v) with. autoclaving for 30 min at 10 psi resulted in maximum saccharification of corn‐cob. However, the order of susceptibility of substrates to enzymatic attack was corn‐cob > wheat straw > sugarcane bagasse > groundnut shell. Increase in enzyme concentration (1–4 IU ml−1) and treatment duration (12–72 h) improved saccharification, but increases in substrate concentration (>5.0%, w/v) had an inhibitory effect on the hydrolytic ability of the cellulase enzyme complex. Of the various substrate‐acid ratios tested, a ratio of 1:8 was found to be optimal for the eflcient hydrolysis of the substrates under study.