Diffusion and thermal stability of phenolic compounds during fortified rice rehydration process

• Mass transfer of phenolics inside rice kernels was governed by Fickian diffusion.
• Leaching of phenolics in rehydration medium followed a 1st order kinetics pattern.
• Phenolics inside rice grains presented good thermal stability during rehydration.
• Fortified rice maintained a great part of its phenolic content after rehydration.

The diffusivity of phenolic constituents in rice as well as the kinetics of their leaching in boiling water were studied during fortified rice rehydration. Phenolic concentrations in fortified rice grains during cooking were modeled using a Fickian diffusion model and seemed to be in good agreement with the calculated data. The apparent diffusivity of 4 specific phenolic compounds was estimated to be in the range of 4.90–16.97*10−10 m2/s and the retention of these compounds in rehydrated rice was found to be at least 24% of their amount in dry fortified rice. This indicates that a significant amount of antioxidants was not released even after intense thermal processing in excess water and this may be a result of strong interactions between rice macromolecules and phenolic antioxidants. Moreover, a great thermal stability of individual phenolic compounds in fortified rice was observed during rehydration at boiling temperatures.