Sequential statistical optimization of lactose-based medium and process variables for inulinase production from Penicillium oxalicum BGPUP-4.

A statistical tool of response surface methodology was used sequentially to optimise lactose-based medium and process variables for inulinase production from Penicillium oxalicum BGPUP-4. Two-level CCRD with four variables, for each design, was used for the optimization study. The independent variables: lactose 1-3%, NH4H2PO4 0.2-0.5%, NaNO3 0.2-0.5%, pH 5.0-7.0 (design-1); temperature 25-35 °C, incubation time 4.0-6.0 days, inoculum size 1.0-3.0 mycelial agar discs and agitation 100-200 rpm (design-2) were selected for the present investigation. The optimised medium variables (lactose 3.70%, NH4H2PO4 0.35%, NaNO3 0.35% and pH 6.0) produced 44.44 (IU/ml) and 0.38 (g dry wt./50 ml) of inulinase and biomass yield, respectively. Thereafter, the optimization of process conditions (temperature 25 °C, incubation time 5 days, inoculum size 2 mycelial agar discs and agitation 150 rpm), increased the inulinase production 50.45 (IU/ml) and biomass yield 0.26 (g dry wt./50 ml). The good agreement between experimental and predicted values in both the designs, the coefficient of determination (R2 ) greater than 0.90 and very close to 1.0 shows an appropriate fitness of the polynomial quadratic models.