Optimization of conditions for production of pectinase in solid-state fermentation with Aspergillus flavus using dried Assam lemon peel powder as substrate

Abstract

The culture conditions for pectinase production with Aspergillus flavus by solid-state fermentation (SSF) using dried Assam lemon peel were optimized and the pectinase was used for clarification of grape juice. A central composite rotatable design (CCRD) was used for optimization experiments with moisture content (50–90 %), incubation temperature (20–60 ℃), incubation time (96 h–192 h), and urea concentration (0–1 %) as independent variables, and pectinase activity as dependent variable. The optimum conditions for pectinase production obtained were moisture content of 60 %, incubation temperature of 50 ℃, incubation time of 96 h, and urea concentration of 0.30 % with a pectinase activity of 3.68 ± 0.20 U/mL where one unit of pectinase activity corresponds to number of µmole of galacturonic acid released in one minute in 1 % pectin solution at 37 °C and 4.8 pH. The crude pectinase was found to have maximum activity at a temperature of 40 ℃ and pH 4 and had an apparent V_max and K_m of 6.10 U/mL and 6.62 mg/mL respectively. The grape juice clarified using the crude pectinase showed decreased optical density (1.45 ± 0.06 to 1.17 ± 0.07) and viscosity (1.76 ± 0.10 to 1.46 ± 0.07 mPa.s) and increased reducing sugar content (13.90 ± 0.10 to 16.96 ± 0.06 g/100 mL juice), and total soluble solids (17.77 ± 0.16 to 18.50 ± 0.30 °Brix).