The R2 values of models for this study were higher than 0.70, indicating a good fit, as shown in Table 3. All of the lacks of fit tests were not significant, which also showed a good fit between the experimental data and the model. The R2 value reflects the suit-ability of the model to represent the real relationship between the selected reaction parameters. Many statistical analyses were used for fitting the model, to judge the experimental error, the statistical significance of the terms in the model, and the suitability of the model (Sanaei, Mahmoodani, See, Yusop, & Babji, 2013). However, there is no reference value stating that higher R2 suggests a good model and lower R2 suggests a poor model.