Effect of different retrogradation conditions on the physicochemical and sensory properties of rice

Starch retrogradation significantly compromises the quality of ready-to-eat rice products. A systematic understanding of how retrogradation conditions affect different rice varieties is crucial for quality control and product development. This study investigated the effects of different retrogradation conditions (4 °C and 25 °C for 12, 24 and 36 h) on the physicochemical and sensory properties of three rice varieties: japonica (14.51 % amylose), indica (20.68 % amylose), and glutinous rice (1.16 % amylose). The results indicated a significant decrease in the quality of retrograded rice compared to fresh rice. The extent of quality deterioration upon retrogradation varied significantly among the varieties. Indica rice exhibited the most pronounced changes in textural and sensory properties, while glutinous rice showed the greatest stability. The rice quality varied under different retrogradation conditions. At the same retrogradation temperature, all three types of rice showed a tendency of deepening color, increasing hardness and chewiness, and decreasing adhesiveness and springiness with the extension of retrogradation time. Meanwhile, a gradual increase in the contents of slowly digestible starch (SDS) and resistant starch (RS) was observed. Under the 4 °C condition, both the RS content and hardness of japonica, indica, and glutinous rice reached their maximum values after 36 h of retrogradation. The RS contents were 16.13 %, 19.56 %, and 12.25 %, while the hardness values were 1794.89, 1984.89, and 1397.49, respectively. The bound and immobile water contents gradually decreased, the free water contents increased, the short-range ordering and relative crystallinity increased. At the same retrogradation time, the rice retrogradation at 4 °C exhibited darker color, higher hardness and higher RS content compared to the rice retrogradation at 25 °C. The study elucidated the changes in physicochemical and sensory properties of rice under varying retrogradation conditions, providing a theoretical basis for the research and development of aseptic convenience rice, short-shelf-life instant rice, and other ready-to-eat rice products.