Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 degrees C and 37 degrees C, respectively. Pasting study indicated that rice samples stored at 37 degrees C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 degrees C, aged rice (stored at 37 degrees C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 degrees C caused a significant increase in the amount of cell wall remnants along the storage at 37 degrees C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties. (C) 2016 Published by Elsevier Ltd.