Modelling starch phase transitions and water uptake of rice kernels during cooking

• Starch gelatinization and fusion transitions modelled together for the first time.
• The model parameters were fitted with conservative water content functions.
• Water uptake kinetics of rice kernels were determined between 50 °C and 100 °C.
• Original model of equilibrium water uptake from transition levels is proposed.

To model the cooking processes of rice, starch gelatinization, the level of fusion of the amylose-lipid complex, and equilibrium water uptake have to be known for any given condition. Starch phase transitions were measured by DSC in two milled Korean round rice kernels whose water contents ranged from 0.18 to 4.7 g g−1 db. Two to three partially overlapping transitions were assessed. Starch thermal transitions were modelled using a double step approach. First, a mechanistic double sigmoid model was fitted with DSC data for any water content value. Each parameter of the mechanistic model was then modelled with conservative empirical water content functions. In this way we obtained an explicit form of phase transition levels as a function of both temperature and water content. In parallel, the water uptake kinetics of rice kernels was determined in the temperature range of 50 °C–100 °C. Equilibrium water uptake was found to be linked to starch phase transitions and a model was built to calculate equilibrium water uptake as a function of modelled starch gelatinization and amylose-lipid complex fusion levels.