Multiple effects of oil addition and freezing-reheating treatment on the in vitro starch digestibility of rice grains

The objective of this study was to investigate the multiple effects of the addition of oils and freezing-reheating treatment, which are characteristics of frozen rice, on the starch digestibility of rice grains. Either rapeseed oil or its emulsifier was added to the polished grains at a weight ratio of 1.2%, stirred, and cooked. Cooked grains were frozen, stored in a freezer at -20 °C, and reheated in a microwave oven to prepare frozen-reheated grains. While the equilibrium concentration of starch hydrolysis (C_∞) was significantly higher for frozen-reheated grains (98.30%–110.92%) than for cooked grains (95.35%–97.91%), the kinetic constant (k) was significantly lower for frozen-reheated grains (7.39 × 10⁻³–8.98 × 10⁻³ min⁻¹) than for cooked grains (9.16 × 10⁻³–9.45 × 10⁻³ min⁻¹). The eGI ranged from 86.42 to 89.98 and was not significantly affected by the addition of oils, freezing-reheating, or the interaction. The results suggested that C_∞ and k of rice grains was not affected by the addition of 1.2% of oils and interaction but was affected by freezing-reheating.