Optimization of cellulase production by Aspergillus nidulans: application in the biosoftening of cotton fibers

The enhancement of the cellulase activity of Aspergillus nidulans by combinational optimization technique and the usage of cellulase for the biofinishing of cotton fibers were investigated in this study. The strain isolated from decayed, outer shell of Arachis hypogaea was compared for the first time for its ability to produce cellulolytic enzyme in shaken cultures using the optimized media formulated by combinational statistical approach using one factor at a time methodology (OFAT), Plackett Burmann Methodology (PB) and response surface methodology (RSM). A four-factor-five-level central composite design (CCD) was employed to determine the maximum activity of cellulase at optimum levels of carboxy methyl cellulose (CMC), ammonium nitrate and potassium dihydrogen phosphate at varying pH values. The cellulase activity is the best so far obtained with this strain of Aspergillus nidulans. The optimum values of the parameters studied were found to be 0.75 mg/l, 1.5 mg/l, 0.01 mg/l, and 2.15 g/l for KH₂PO₄, NH₄NO₃, Thiamine HCl and CMC, respectively at pH 6.0. This optimization led to the fine tuning of the cellulase production, thereby enhancing the cellulase activity from 4.91 to 60.54 U/ml. This cellulase of higher activity was employed in the biofinishing of the cotton fibers. The results of the scanning electron microscope (SEM) analysis after the treatment favored the fact that maximum surface finishing was achieved at a cotton fiber concentration of 15% (w/v) at 45°C and pH 5.0 using cellulase (60.54 U/ml) at 16th hour of the treatment. A probable mechanism of enzymatic finishing of cotton fibers has also been represented.