Optimization of enzymatic hydrolysis of water hyacinth by Trichoderma reesei vis-a-vis production of fermentable sugars

Aquatic weed water hyacinth was evaluated for its potential to be used as feedstock for fermentable sugar production via enzymatic hydrolysis. Critical factors (pretreatment of substrate, concentration of substrate, incubation period, pH, incubation temperature) affecting enzymatic hydrolysis of water hyacinth were optimised for maximum production of fermentable sugars. Enzyme (mainly cellulase) produced by Trichoderma reesei ATCC 26921 in a simple medium containing the plant biomass as the sole carbon source was directly used at a particular concentration for hydrolysis. It was observed that acid-alkali pretreated water hyacinth was far more accessible to cellulolytic enzymes than untreated one and hence was hydrolyzed to a greater extent. Maximum hydrolysis (41.7%) was obtained with 4% (w/v) pretreated water hyacinth after 72 h of incubation at pH 5.2 and at a temperature of 45 °C. With a view to enhance the percentage of enzymatic hydrolysis, culture metabolite (enzyme source) of T. reesei was supplemented with enzyme from a β-glucosidase mutant, Aspergillus phoenicis . This β-glucosidase enriched cellulase preparation facilitated further enhancement (49.7%) of hydrolysis at FPase to β-glucosidase ratio of 1:1.2. Gas-liquid-chromatographic analysis of the hydrolyzed broth, thus obtained under optimal conditions, revealed the presence of glucose (12.5 g l−1) as the most predominant fermentable sugar besides having the presence of xylose, arabinose, mannose and galactose. This widens up the feasibility of utilising such hydrolysate as a cheap carbon source (glucose and to some extent xylose) for yeast fermentation to produce fuel ethanol