Kinetic analysis of rice grain firmness during soaking and its relationship to textural-related properties

This study investigated the relationship among textural-related properties (moisture content, leached material content, and grain dimensions), tissue structure, and surface and overall firmness of rice grains during soaking, together with a kinetic analysis of firmness changes. Polished rice grains were soaked in distilled water at 30–90 °C for 0–60 min. Temperature dependence was evaluated using the Arrhenius equation by fitting both exponential and Page models. Surface and overall firmness were significantly correlated with the textural-related properties and were affected by the presence of a gelatinized starch layer and internal voids. Both models fit the experimental surface–firmness data across all temperatures. The rate constant of surface-firmness reduction exhibited a linear temperature dependence, with the activation energies of 51.3 kJ mol −1 (exponential model, R 2 = 0.89) and 21.3 kJ mol −1 (Page models, R 2 = 0.95). • Rice grain firmness decreased rapidly with soaking temperature and time • Firmness correlated with moisture and leached material contents • Cracks, voids, and a gelatinized layer governed temperature-dependent softening • Surface-firmness kinetics were well described by exponential and Page models • Arrhenius analysis quantified the temperature sensitivity of rice grain softening.