ratio of fried rice crackers significantly (P < 0.05) depended on frying temperature (X22) as shown in Table 6.
The R2 determination coefficients of moisture content,
oil content and expansion ratio were high (R2> 0.9) with fitted quadratic equations (Table 6). The P values of lack of fit were also large.
This indicated that the quadratic regression model was adequate for optimization.
The contour plots of moisture content (Y1), oil content (Y2) and expansion ratio (Y3) of fried rice crackers as affected by fish powder content (X1) and frying temperature (X2), at fixed frying time (X3¼ 0) are shown in Fig. 4