Statistical optimization of cellulases production by Aspergillus niger HQ-1 in solid-state fermentation and partial enzymatic characterization of cellulases on hydrolyzing chitosan

Abstract

Cultivation conditions of cellulases production by Aspergillus niger HQ-1 in solid-state fermentation (SSF) were optimized. Furthermore, partial enzymatic characterization of the crude cellulases on hydrolyzing chitosan was studied. The moisture content, cultivation temperature, and initial culture pH were identified by Plackett-Burman design (PBD) as the significant factors for cellulases activities. The method of steepest ascent was undertaken to determine the optimal regions of the three significant factors. Box-Behnken design (BBD) and response surface analysis were adopted to further investigate the interaction effects between the three variables on cellulases activities and to determine the optimal values of the variables. The optimal ranges of moisture content, cultivation temperature and initial culture pH were 70.3-70.6%, 33.5-33.7°C and 4.626-4.662, respectively. Under the optimized conditions, endoglucanase activity, filter paper activity (FPA) and β-glucosidase activity were 305.103, 42.432 and 158.527 U/g, respectively. The optimal pH and temperature of the crude enzymes for chitosan hydrolysis were determined to be 5.6 and 50°C, respectively. The chitosanolytic activity was enhanced by metallic ions in order of Mn 2+, Mg 2+, Ca 2+ and K +, but inhibited by Zn 2+, Ba 2+, Co 2+, Fe 3+, Cu 2+ and Ag +. © Springer-Verlag and the University of Milan 2011.