Statistical optimization of cellulases production by Penicillium chrysogenum QML-2 under solid-state fermentation and primary application to chitosan hydrolysis

Abstract

Solid-state fermentation conditions for cellulases production by a newly isolated Penicillium chrysogenum QML-2 were investigated using statistical methods. At first, significant variables for cellulases production including (NH(4))(2)SO(4), initial pH and inoculum size were screened by using Plackett-Burman Design. Then the optimal regions of the significant variables were investigated by using the method of steepest ascent. Finally, central composite design and response surface analysis were adopted to determine the optimal values of the significant variables and investigate the combined effects of each variable's pair on cellulases production. The results showed that the optimal ranges of (NH(4))(2)SO(4) concentration, initial pH and inoculum size for three types of cellulases activities were 1.97-2.15 g, pH 4.32-4.41 and 13.3-13.7% (v/w), respectively. Using the mixture of corn stover powder and wheat bran (CSP/WB, 1/1) as carbon source, the optimization resulted in 370.15, 101.76 and 321.56 U/g for maximal endoglucanase activity, filter paper activity and β-glucosidase activity, respectively. Compared with maximum values of cellulases activities (endoglucanase activity 85.21 U/g, filter paper activity 16.62 U/g and β-glucosidase activity 67.68 U/g) obtained under unoptimized conditions, the optimization resulted in 3.34, 5.12 and 3.75 folds improvement for endoglucanase activity, filter paper activity and β-glucosidase activity, respectively. For chitosan hydrolysis, the crude cellulases had the optimal temperature of 55°C, pH of 4.4 and exhibited Michaelis constant (K (m)) value of 8.34 mg/ml and maximum velocity (V (max)) of 2.21 μmol glucosamine/min by 1 ml of the crude cellulases.