found similar results in soy-based extrudates. The regression equation for the relationship between L value
(YL) and independent variables in terms of coded variables is presented in Table 3, 2FI model was selected according to Design Expert 6.0, the “a” and “b” value did not yield any significant model, so only Lwas selected as the color variable. ANOVA analysis showed that linear term of protein content, and interaction between protein content and moisture content significantly affected the L value. The response surface plot of L value of extrudates are presented in Fig. 4.
They showed that the protein content had a negative impact on L value. But L value increased with deceasing feed moisture when the protein content was at low, and L value also increased with increasing processing temperature. This may happened due to Maillard reaction between amino groups and carbonyl groups, which leads to browning in the extrudates. Low feed moisture and high processing temperature are good candidates for the Maillard reaction