Quality Changes and Shelf Life Prediction of Extruded Rice at Different Storage Temperatures

To investigate the quality changes of extruded restructured rice during storage at different temperatures, the changes in physicochemical properties, rehydration characteristics, and sensory qualities were analyzed during storage at 25, 35, 45 and 55 ℃. The rehydration time index was fitted by kinetic equations, and a shelf-life prediction model was established in conjunction with the Arrhenius equation. Finally, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were employed to verify the occurrence of starch retrogradation, thereby explaining the cause of the prolonged rehydration time of extruded restructured rice. The results indicated that with the extension of storage time, the L^* value and sensory score of extruded rice gradually decreased, while the b^* value, rehydration time, hardness and chewability gradually increased, and the higher the storage temperature, the faster the rate of change. The increase rates of rehydration time at 25, 35, 45 and 55 ℃ storage at 120 days were 7.14%, 23.86%, 31% and 47.57%, respectively. The kinetic model using rehydration time as the index had the highest fit with the zero-order kinetic model, and the error of the shelf-life prediction model based on this was less than 10%. In addition, XRD analysis confirmed that the starch crystal structure became more ordered of extruded rice during storage, DSC analysis also showed that the gelatinization enthalpy significantly increased with the storage time, and gelatinization enthalpy increased to 1481.33 J/g after 120 days storage at 45 ℃. The apparent morphology of the microstructure became rough gradually. Consequently, rehydration time was considered as the key index of quality deterioration of extruded rice during storage. The shelf-life prediction model established based on this is relatively reliable. The prolongation of rehydration time during storage is related to starch retrogradation.