In this study a two-step approach was applied in order to investigate the effect of seven factors including: concentration of ammonium sulphate، potassium dihydrogen phosphate، date pulp، pH، inoculums size، agitation speed and fermentation time on the pectinlyase production by Aspergillus niger. At first step، the effects of these variables were studied using fractional factorial design. According to obtained results three factors، pH، ammonium sulphate concentration and fermentation time were considered for further study. Second step was carried out by using central composite design (CCD) in order to find optimum conditions of pH، ammonium sulphate concentration and fermentation time. After analysis of CCD، optimum condition for maximization of pectinlyase activity determined as follow: ammonium sulphate concentration 0. 35%، fermentation time، 73. 93 hours and pH، 4. 82. Enzyme activity at this optimum condition was 1. 38 U. ml -1.
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