Effect of sodium trimetaphosphate modification on the structure and rheological properties of zein

The modification of zein with sodium trimetaphosphate (STMP) as a cross-linking agent was studied. The effects of the mass ratio of STMP to zein (R-S/Z), pH, reaction temperature and time on the rheological properties of modified zein solution (Z-SP) were evaluated. By using response surface methodology, the optimal modification conditions were also determined as following: R-S/Z 0.03, pH 6.8, reaction time 2 h, reaction temperature 25 degrees C. Under these conditions, the observed shear stress of Z-SP solution was 35.0025 Pa, close to the predicted value. Compared with natural zein, the viscosity of Z-SP increased with the increasing shear rate, which was attributed to the structural changes, as evidenced by circular dichroism (CD) and Fourier transform infrared (FT-IR) analysis.