Morphological and physicochemical properties of rice grains submitted to rapid parboiling by microwave irradiation

Abstract

This study evaluates the effects of microwave irradiation used for the rapid parboiling process on the morphological, technological, and structural properties of rice grains. Parboiling was performed by microwave under the same temperature and soaking and autoclaving conditions as those used in the conventional process. However, two heating stages were used at different microwave irradiation exposure times: (a) first stage (FS): 10, 20, 30 or 40 min; (b) second stage (SS): 0, 5, or 10 min. The rice grains submitted to the FS of microwave irradiation absorbed more water and lost less leached solids compared to those parboiled using the conventional method. Unlike conventional parboiling, microwave irradiation decreased the cooking time of the rice grains and modified their protein solubility. Furthermore, this technique modified the paste properties, morphology and crystalline structure of grains. These findings suggest a great impact on chemical and physic characteristics of parboiled rice by microwave irradiation. The microwave irradiation in the parboiling process significantly reduced the processing time (one-tenth as long than that required for the conventional process) and allowed obtaining of parboiled rice grains with greater whiteness and with faster cooking.