Effect of the Ratio of Soluble and Insoluble Dietary Fiber from Rice Bran with Extrusion Cooking Treatment on Pasting, Thermal, and Structural Properties of Rice Starch Gel

This study aims to investigate the effect of different ratios of soluble and insoluble dietary fiber (0/100, 25/75, 40/60, 55/45, 70/30, 85/15, 100/0) in rice bran treated with or without extrusion cooking on the physicochemical and structural properties of rice starch. As the ratio of soluble dietary fiber (SDF) increases, the PV (peak viscosity), FV (final viscosity), SB (setback value), and BD (breakdown value) of starch are significantly decreased, indicating that a higher SDF ratio can delay the short-term retrogradation of starch. Compared with the unextruded rice bran SDF/IDF starch gel, the content of weak bond water and free water in the extruded rice bran SDF/IDF starch gel is higher while the content of strong bond water in the starch gel is lower at the same SDF/IDF ratio. Meanwhile, for the results X-ray diffraction (XRD) and fourier transform infrared spectrum (FTIR), the rice starch with the extruded rice bran SDF/IDF ratio of 25:75 shows the lowest relative crystallinity of 3.48% and the lowest peak to height ratio of FTIR (1047 cm-1/1022 cm-1) of 1.0746, suggesting that the inhibition effect on rice starch retrogradation is better. This may be beneficial for the utilization of different ratios of SDF/IDF from extruded rice bran and physicochemical properties improvement of rice starch gel. Compared with the unextruded rice bran SDF/IDF starch gel, the PV, FV, enthalpy, and hardness of the extruded rice bran SDF/IDF starch gel are decreased significantly with the increase of the SDF ratio. Rice starch with 25:75 ratio of SDF/IDF from extruded rice bran shows the lowest relative crystallinity, suggesting the stronger inhibition effect on rice starch retrogradation. image