The levels of the independent parameters were based on the preliminary experimental results. A rotatable central composite design was selected for the optimization of process variables at 5 levels with 20 runs, including six replicates at the central point. The range and levels of independent variables were presented in their coded forms in Table 1. The experimental data were fitted to second-order polynomial models, which expressed the yield of TP (Y1), TFA (Y2), ABTS radical scavenging activity (Y3) and DPPH radical scavenging activity (Y4) as a function of the independent variables as follows: