Generating Fermentable Sugars from Rice Straw Using Functionally Active Cellulolytic Enzymes from Aspergillus niger HO (original) (raw)

Among the three Aspergillus spp. (A. niger, A. oryzae, and A. f umigatus) screened for cellulolytic enzyme production potential, A. niger produced cellulolytic enzyme in relatively higher concentrations than the other two isolates. Enzyme produced by all three isolates was optimally active at pH 5.0. Cellulases from A. niger and A. f umigatus were optimally active at 55°C, while the enzyme from A. oryzae showed optimum activity at 50°C. Cellulase from A. niger and A. f umigatus retained more than 80 and 70% activity, respectively, while cellulase from A. oryzae could retain only 20% activity at 55°C after 12 h. Cellulase from A. niger exhibited better stability at higher temperatures than the enzyme from the other two Aspergillus spp., showing half-life (t 1/2) of about 5 and 3 h at 70 and 80°C, respectively. Zymogram revealed multiple forms of endoglucanase, cellobiohydrolase, and β-glucosidase with molecular mass ranging between 28 and 154 kDa for cellulase from all three isolates. Hydrolysis of rice straw at 12.5% (w/v) with crude cellulase from A. niger HO resulted in fermentable sugar concentration and productivity of 66.2 g L −1 and 2.75 g L −1 h −1 , respectively, showing potential for the reported enzyme in biofuel industry.