The Effect of Acid Treatment and Freeze-Thaw Cycle on Textural Properties and Microstructure of Cooked Aged Rice

This research aims to improve frozen cooked aged rice's textural properties using lime juice, citric acid, and ascorbic acid solutions. Aged (12 months) rice is cooked and freeze-thawed up to 3 cycles. Cooked fresh rice (0.7 months) is used as a reference. Addition of acid significantly decreases hardness but significantly increases stickiness for freeze-thawed, cooked, aged rice (p <= 0.05). Scanning electron micrographs show a rough surface on cooked rice after repeated freeze-thaw cycles, especially for cooked aged rice. However, the microstructure of acid treated cooked aged rice has a smoother surface than untreated. These results correlate with decreased starch retrogradation in acid treated cooked aged rice. Gel electrophoresis shows disulfide bond formation in aged rice protein which restricted granular swelling and gelatinization. Addition of acid did not cleave aged rice protein's disulfide bonds but reduces protein content. These results demonstrate addition of acid improves frozen cooked aged rice's texture.