Modeling the hydration step of the rice (Oryza sativa) parboiling process

- Hydration step promoted the endothermic phenomenon of gelatinization.
- The parboiling process does not require subsequent steps to hydration.
- It was possible to simulate the 3-dimensional mass transfer process during hydration of the rice.
- Thermodynamic properties confirmed the hydration process is not spontaneous.

This work deals with the thermal, morphological, and kinetic characteristics of rice during hydration, as well as the modeling of the process. Rice grains were subjected to different hydrothermal conditions and showed no degradation, but presented an endothermic transition corresponding to gelatinization at 53.8 °C. During hydration, the water absorption rate increased with temperature and grain morphological changes were observed only after gelatinization. There was a good agreement between the predictions of the theoretical model based on Fick's second law and the experimental results (maximum error of 2.067%); the phenomenological model built numerically was able to represent (3D and 2D) moisture transfer into the grain with an error of 1.708%. The parameters adjusted to the different models confirmed the effect of temperature on the process, and the thermodynamic properties (enthalpy, entropy, and Gibbs free energy) determined showed that hydration happened with non-spontaneous exothermic transformations.