Effects of moisture content and retrogradation on structure and properties of indica rice flour and starch gels

The physicochemical, functional, and sensory attributes of indica rice gels is strongly influenced by starch retrogradation. The objective of this study was to improve the cooking and textural qualities of indica rice gels by controlling retrogradation conditions. Differential scanning calorimetry (DSC), infrared spectroscopy (FITR), small angle X-ray scattering (SAXS), wide angle X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses showed that retrogradation modified the molecular interactions, increased the crystallinity, and altered the microstructure of indica rice gels. Retrogradation of rice gels in the presence of 40% moisture for 12 h significantly improved their cooking and rehydration properties. The rehydration rate of indica rice starch and flour gels increased by around 10.62% and 8.41%, while the cooking loss decreased by about 24.63% and 29.30%, respectively, compared to the non-retrograded controls. The textural attributes of these gels were also influenced by retrogradation: the tensile increased by 23.48% and 37.13%, the hardness increased by 37.30% and 29.86%, the springiness increased by 4.94% and 2.43%, and the adhesiveness decreased by 41.62% and 37.28%, respectively. The presence of protein in the indica rice flour significantly inhibited the degree of retrogradation. The results showed that control retrogradation can be used to enhance the cooking and quality attributes of indica rice gels. This knowledge may be useful for improving the properties of rice-based food gels.