Lignocellulosic biomass holds remarkable potential for conversion into commodity products presenting dual advantage of sustainable resource supply and environmental quality. Though their utilization does not compete with food and feed demand, its bioconversion and utilizability is facilitated by pretreatment. The effect of the substrate pre-treatment using acid and alkali at two different concentrations (0.5 and 2 M) for two different residence timings (1 and 3 h) on cellulase production from corncob, corn straw and bagasse was studied using Aspergillus niger AH3. The strain was inoculated into 10 g/L of the processed pre-treated lignocellulosic substrates previously added to batches of the Mandels basal medium. The pH of the medium was adjusted to optimum (4.8) and the flasks with the contents autoclaved, thereafter fermentation begun. Samples of each flask were taken aseptically at regular interval (24 h) throughout the growth phase until the enzyme activity peaked off (between 110 and 170 h), centrifuged and the clear supernatant was used for the enzyme assay. Enzyme expression in all the pretreated biomass increased steadily from day one and peaked off at day four or five for the alkali pretreated residues whereas it was at day six for acid pretreated residues. Generally for the alkali treated residues irrespective of residence time, maximum cellulase yield was at day 5 while for the acid treated residues, maximum cellulase yield was at day 6. Enzyme yield from residues treated for longer period (3 h) using alkali when compared to those using acid under the same condition of fermentation was highly significant. The alkali treated residues showed higher cellulase yield than the acid treated residues. Highest cellulase activity (0.06777 IU/ml/min) was displayed by the organism grown on bagasse substrate pretreated with 2M NaOH for one hour. The proximate analysis of the cellulosic residues differed from one substrate to another, with the bagasse being the best. Pulverized substrates syndicated with alkali pretreatment using 2 M NaOH for one hour was optimal for cellulase production from the cellulosic residues.
Key words: Lignocellulosic biomass, utilization, pretreatment, cellulase, substrates, Aspergillus niger AH3, fermentation, supernatant, substrate
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