Hydrolytic Performance of Aspergillus niger and Trichoderma reesei Cellulases on Lignocellulosic Industrial Pineapple Waste Intended for Bioethanol Production

Abstract

Purpose: The hydrolytic action of Aspergillus niger and Trichoderma reesei commercial cellulases, alone or combined with A. niger hemicellulase, against industrial pineapple waste as a previous step to produce bioethanol was investigated. Methods: Enzymatic hydrolysis experiments were conducted in static conditions in an incubation oven, by adding the corresponding enzyme mixture to the pineapple waste (combinations of 0, 0.1, 0.2 and 0.4 (w/w) of cellulase from A. niger or T. reesei and hemicellulase from A. niger). pH and total soluble solids were examined along the treatments, and the sugar profile in the final hydrolysates was evaluated by high-performance anion-exchange chromatography. Results: Trichoderma reesei cellulase exhibited a significantly faster initial hydrolysing rate than A. niger cellulase (0.258 ± 0.004 vs. 0.15 ± 0.07, for the maximum enzyme concentrations assayed), although differences regarding soluble sugars increments were not significant at the end of the treatment (0.349 ± 0.009 vs. 0.34 ± 0.05). Glucose, fructose, sucrose, arabinose, xylose and cellobiose were identified in the hydrolysates. Increasing enzyme concentration (cellulase or hemicellulase) produced an increase in total and fermentable sugars released (17 and 11%, respectively, for the maximum enzymatic concentration assayed); besides, a synergistic effect of combining hemicellulase and cellulase was identified. Accumulation of cellobiose (up to 4.4 g/L), which may slow down hydrolysis, evidenced the weaker β-glucosidase activity of T. reesei cellulase. Due to its performance and the lower cost of the enzyme, A. niger cellulase was chosen as an alternative. Conclusions: Commercial A. niger cellulase represents an efficient alternative to T. reesei cellulase for the saccharification of industrial pineapple waste, especially when combined with a hemicellulase. Total sugars present in the final hydrolysates indicated that A. niger cellulase performed similarly at a lower cost, with no cellobiose accumulation. However, if processing time is a limiting factor, T. reesei cellulase could be the one preferred.