where Y is the predicted response; b0 denotes the model intercept; bi, bii and bij represent the coefficients of the linear, quadratic and interactive effect, respectively; Xi, and Xj are the coded independent variables; and k is equal to the number of the tested factors (k = 3). The Pearson correlation coefficients were calculated using the mean values (n = 17) to determine the degree of association between the pairwise variables.