Model application: Hydration and gelatinization during rice parboiling

The rate of water absorption of a local rough rice variety at temperatures below and above the corresponding gelatinization temperature was investigat ed. A mathematical model that describes water diffusion and gelatinization within the grain, was used to simulate rice parboiling. The data were proce ssed using a nonlinear regression procedure to calculate the diffusion coef ficients and reaction rate constants in the temperature range 35-95 degrees C. Both coefficients follow an Arrhenius temperature dependency with a brea k point at 77 degreesC, where rapid gelatinization of rice begins. From the comparison between the activation energies for diffusion and reaction it i s concluded that the parboiling process is limited by the reaction of starc h with water below 77 degreesC and by diffusion of water above 77 degreesC.