insignificant (P > 0.05). Among quadratic coefficients only the DPPH
velocity was insignificant (P > 0.05).
The three-dimensional (3D) response surface and two dimensional
(2D) contour plots are shown in Fig. 1. The plots give a better
visualization. The shapes of the contour plots indicate whether
the interactions between the corresponding variables are significant
or not. The elliptical contour plots indicate that the mutual
interactions between the corresponding variables are significant.
The predicted S/N was 81.0 with the following examined
variables: DPPH concentration of 24.70g/mL, DPPH velocity of
0.45 mL/min, reaction tank length of 16.65 m. The optimum parameters
were DPPH concentration of 25.0g/mL, DPPH velocity of
0.45 mL/min, reaction take length of 15.0 m.
In order to verify the applicability of the model equations, a
verification test was carried out under the optimal conditions mentioned
above. Under the optimal conditions the experimental yield
was 76.3 (n = 3), which is consistent with the predicted value of
81.0. The difference between 76.3 and 81.0 (n = 3) were not significant
(P > 0.05) which confirmed that the response model was
accurate and adequate to reflect the experimental data.