Aging of low and high amylose rice at elevated temperature: Mechanism and predictive modeling

• Aging of low and high amylose rice at 39.2 °C was monitored.
• Change in protein molecular weight was the major mechanism of rice aging.
• Change in selected quality parameters was fitted with fractional conversion model.
• Rate of the property changes was different among low- and high-amylose cultivars.
• NIR-based models were constructed for 5 quality parameters of fresh and aged rice.

The objective of this research was to study the changes in physicochemical properties of rice during elevated temperature storage. Paddy of three rice cultivars with low amylose content (9–11%) and the other three with high amylose content (23–25%) was stored at 39.2 °C and 43.1% relative humidity up to 31 weeks. Drastic changes in moisture content and some parameters representing cooking qualities, cooked rice texture and pasting properties occurred during the first four weeks of aging. At similar aging time, low amylose rice had higher adhesiveness, peak viscosity and breakdown, but had lower pasting temperature than high amylose rice. Time-dependent change in adhesiveness and pasting temperature was predicted by fractional conversion model (0.60 ≤ R2 ≤ 0.94). Difference among rate constant values of the data from low and high amylose rice was found. Proportion of high molecular weight proteins (>225 kDa) tended to increase over time. However, enthalpy of amylose-lipid complex melting fluctuated during storage. Changes in protein molecular weight pattern could thus be key mechanism of rice aging at elevated temperature. NIR-based predictive models for minimum cooking time, adhesiveness, pasting temperature, peak viscosity, and breakdown of rice samples were established (R2 of calibration ≥ 0.81; R2 of validation ≥ 0.87).