Effect of rice ageing and freeze‐thaw cycle on textural properties of cooked rice (Oryza sativaL.) cv. Khao Dawk Mali 105

Abstract

Summary This study investigated the effect of rice grain ageing (0.7–12 months) and freeze‐thaw 1–5 cycles on the textural properties of cooked rice. The cooked rice from aged rice grains was freezing and thawing up to five cycles. Ageing of the rice grain increased the hardness and decreased the stickiness of the cooked rice. Repeated freeze‐thaw cycles caused an increase in hardness and a decrease in stickiness of aged cooked rice. Scanning electron micrographs showed a rough surface on the cooked rice after repeated freeze‐thaw cycles, especially for cooked rice from rice aged for 12 months. Differential scanning calorimetry and X‐ray diffraction showed increased starch retrogradation with increased freeze‐thaw cycles. The gelatinisation temperature and gelatinisation enthalpy increased when rice was aged for longer periods. Thus, ageing of rice and the number of freeze‐thaw cycles influence the textural properties of cooked rice.

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

“…The enthalpy of melting retrograded amylopectin (Δ H ) for cooked rice after three freeze‐thaw cycles showed an increase with longer rice aging. Similar results have been reported by Katekhong and Charoenrein . Moreover, treating cooked aged rice with 3 g kg −1 citric acid or ascorbic acid solutions revealed a significant ( p < 0.05) decrease in Δ H value when compared to the untreated cooked aged rice.…”

“…The hardness value of all samples increased, while the stickiness decreased after repeated freeze‐thaw cycles, especially for cooked aged rice. These changes were partially due to the retrogradation of starch granules . Treatment with citric acid and ascorbic acid solutions decreased the hardness value and increased the stickiness value of cooked 12 month aged rice as compared to the untreated cooked 12 month aged rice.…”

“…An increase in the hardness and a decrease in the stickiness of cooked rice after repeated freeze‐thaw cycles could have resulted from amylopectin retrogradation . Therefore, a DSC was used to determine the enthalpy of melting retrograded amylopectin in unfrozen and freeze‐thawed cooked rice samples.…”

“…Moreover, the refreezing‐thawing process caused by temperature fluctuation may produce defects in the texture of frozen products making them unacceptable to consumers. Therefore, consumers prefer cooked fresh rice over frozen cooked aged rice subjected to multiple freeze‐thaw cycles because of the extremely hard texture of cooked aged rice …”

Evaluation of Physical, Thermal, Pasting Characteristics and Mineral Profile of Pigmented and Nonpigmented Rice Cultivars

“…In a previous study, Yu et al (2009) stated that the hardness was positively correlated with the amylose contained in rice grain. Rice with higher amylose content was liable to leach more into the cooking water and formed a coating on rice grain, which increases the hardness and leads to significant decreases in stickiness of the cooked rice (Leelayuthsoontorn and Thipayarat 2006;Katekhong and Charoenrein 2014). Amylose, on the contrary, is easier to retrograde and increased the hardness of the cooked rice in a short period.…”