Mathematical modeling of paddy (Oryza sativa) hydration in different thermal conditions assisted by Raman spectroscopy

Abstract

Hydration is the main step of rice parboiling process because it promotes starch gelatinization. The present study presents empirical and phenomenological models for rice hydration at different thermal conditions, as well as evaluations of changes in functional groups of the rice grain during the process. The empirical models of Weibull, Henderson and Pabis, the phenomenological models of Omoto and a diffusive model based on Fick's second law were considered. Additionally Raman Spectroscopy of the grain during hydration is performed. Among the models, Fick's model presents better adherence to the experimental results. It was observed that its effective diffusion coefficient varies with temperature according to Arrhenius equation, providing an estimate of the activation energy of the hydration process. It was also observed that Raman spectra intensity decreases during the hydration process as moisture increases. This suggests that Raman spectroscopy may be employed for monitoring the industrial rice parboiling process.