EFFECTS OF LOW- AND ULTRALOW-TEMPERATURE FREEZING ON RETROGRADATION AND TEXTURAL PROPERTIES OF RICE STARCH GEL DURING STORAGE

Impact of Low-Temperature Storage on the Microstructure, Digestibility, and Absorption Capacity of Cooked Rice

This study examined the effects of low-temperature storage on the microstructural, absorptive, and digestive properties of cooked rice. Cooked rice was refrigerated and stored at 4 °C for 0.5, 1, 3, 5, and 7 days, as well as frozen and preserved at −20, −40, and −80 °C for 0.5, 1, 3, 5, 7, 14, 21, and 28 days. The results indicated that the stored rice samples generally exhibited a higher absorption capacity for oil, cholesterol, and glucose than the freshly cooked rice. In addition, after storage, the digestibility of the cooked rice declined, namely, the rapidly digestible starch (RDS) content and estimated glycemic index (eGI) decreased, whereas the slowly digestible starch (SDS) and resistant starch (RS) content increased. Moreover, the increment of the storage temperatures or the extension of storage periods led to a lower amylolysis efficiency. Scanning electron microscopy (SEM) analysis indicated that storage temperature and duration could effectively modify the micromorphology of the stored rice samples and their digestion. Moreover, microstructural differences after storage and during simulated intestinal digestion could be correlated to the variations in the absorption capacity and digestibility. The findings from this study will be useful in providing alternative storage procedures to prepare rice products with improved nutritional qualities and functional properties.

Studies on effect of temperature and time on textural and rheological properties of starch isolated from traditional rice cultivars of Kashmir (India)

In the present study, the effect of storage temperature and time on the textural and rheological properties of starch gels from seven different rice cultivars having higher amylose content than the hybrid rice varieties were evaluated. Water solubility and swelling power increased with every 10C increase in temperature due to granule swelling and solubilization of starch wherein the maximum solubility was found in starch of Koshkari rice cultivar (0.721 to 13.50) and swelling power in starch of Zag rice cultivar (3.688 to 10.806). However, syneresis in the analyzed rice starch gels had shown a fluctuating trend for each individual cultivar at different storage periods in which the cultivars Zag had shown the highest values of syneresis during storage (4.123 to 4.957%). In the texture profile analysis of starch gel of these cultivars, Mushki Budgi had the highest value of hardness (0.723N), gumminess (36.262) and chewiness (31.056). The turbidity values of gelatinized starch suspensions from different rice cultivars increased progressively during the first 4 days of storage followed by a decrease in the 5th day coupled with slight increase in the 6th day. The highest turbidity was found in Zag ranging from 1.47 to 1.67 during refrigerated storage after 6 days. The rheological analysis revealed that Zag indicated the highest value of TG' (76.96C) whereas cultivars Koshkari and Mushki Kandi had shown the lowest value of TG' (74.34C) upon heating cycle.

PRACTICAL APPLICATIONS

Rheological properties of starch are affected by amylose contents, lipid contents, branch chain length distribution of amylopectin. The starch from different varieties depicted variable textural and rheological properties at various time: temperature combinations. No research has been reported to explore the effect of time and temperature on the textural and rheological properties of starch isolated from these traditional rice cultivars. The starches from traditional rice cultivars (native or indigenous rice cultivars of a region) indicated novel characteristic as compared to other cultivars in terms of their higher amylose content, starch yield, purity, clarity, solubility, syneresis, turbidity, and rheology. The novelty of this research was to exploit the desirable properties of starch obtained from traditional rice cultivars that had better characteristics than the hybrid varieties. This in turn led the various agencies to motivate the farmers to encourage their cultivation, provide an essential platform to scientists to inherit their valuable characteristics.

Impact of Emulsifiers Addition on the Retrogradation of Rice Gels during Low-Temperature Storage

Rice and its products are widely consumed in Asian countries; however, starch retrogradation decreases the quality and shortens the shelf-life of rice foods particularly at low temperature. In this study sucrose ester (SE), glycerol monostearate (GMS), and sodium stearoyl lactylate (SSL) were added to rice flour and corresponding rice gels. Then, gelatinization properties, retrogradation characteristics, texture, and water content of these rice gels were investigated at 4°C and −20°C storage, respectively. The results demonstrated that the rice gels with 0.2% GMS had the lowest retrogradation index (ΔHr/ΔHg) (11.84%) and hardness (1359 g) at 4°C for a 10 d period, which was significantly lower in comparison to control and the other two emulsifiers (P<0.05). Adhesiveness and water content were increased compared to the other samples. Furthermore, the retrogradation of rice gels stored at 4°C was comparatively rapid compared to gels stored at −20°C. Gel samples stored at −20°C were still acceptable for more than 15 days. Thus it was revealed that GMS has the potential to retard starch retrogradation and produce high-quality rice products in preservation.