Title
Optimization of cellulase production under solid-state fermentation by Aspergillus flavus (AT-2) and Aspergillus niger (AT-3) and its impact on stickies and ink particle size of sorted office paper
Authors
DHARM DUTT and ALOK KUMAR

Received December 24, 2012
Published Volume 48 Issue 3-4 March-April
Keywords Aspergillus flavus AT-2, Aspergillus niger AT-3, solid-state fermentation, cellulase activity, stickies, ink particle size

Abstract
Out of 12 fungal strains, two fungal strains, namely Aspergillus flavus AT-2 and Aspergillus niger AT-3, were found to produce maximum cellulase production. The CMCase activities of A. flavus AT-2 and A. niger AT-3 under state solid fermentation (SSF) conditions were of 42.69 and 40.08%, respectively, which was higher than those obtained under submerged fermentation (SmF) conditions. A fungal inoculum dose of 5%, incubation period of 5 days, temperature and pH of 30 °C and 4.8 for A. flavus AT-2 and 35 °C and 5.3 for A. niger AT-3, respectively, solid substrate:moisture content 1:3, rice straw (treated) as carbon source, (NH4)2SO4 + yeast extract as nitrogen source, KH2PO4 as phosphorus source, succinic acid as source of organic acid, Tween-80 as surfactant and cellobiose as source of soluble sugar might be taken as optimal for cellulase production for both fungal strains. The optimum CMCase (17.24 IU/mL), FPase (1.92 IU/mL), β-glucosidase (0.69 IU/mL) and xylanase activities (5.73 IU/mL) and fungal protein concentration (2.90 mg/L) for A. flavus AT-2 and CMCase (24.32 IU/mL), FPase (2.47 IU/mL), β-glucosidase (0.82 IU/mL) and xylanase activities (4.80 IU/mL) and protein concentration (3.07 mg/L) for A. niger AT-3 were taken as optimal under SSF conditions. A. flavus AT-2 and A. niger AT-3 were found active in the pH range of 4.0 to 7.5 and maximum cellulase activity was obtained at pH 5.0 for A. flavus AT-2 (17.31 IU/mL) and at pH 5.5 for A. niger AT-3 (24.50 IU/mL). The optimum temperature for the crude cellulase activities of both fungal strains (A. flavus AT-2, IU/mL and A. niger AT-3, IU/mL) was of 50 °C, and beyond it cellulase activities were found to decrease. Deinking of sorted office paper with cellulase reduced stickies level by 4%, compared to control and concoctions of different enzymes, i.e. cellulose, xylanase, amylase and lipase in different combinations, were capable of removing ink particles of all sizes from the pulp.