Thermal and Rheological Properties of Hydrogels Prepared with Retrograded Waxy Rice Starch Powders

Abstract

Waxy rice starch dispersed in water (50% solids) was gelatinized by heating the dispersion at 121 degrees C for 20 min, and retrograded by storing the paste at 4 degrees C for 2 days. The starch gel was then freeze-dried and ground into powders. The retrograded starch powders were hydrated at 20-30% solid concentration at different temperatures (4 and 23 degrees C), and then thermal and rheological properties were analyzed using the hydrogels. The gel hydrated at 4 degrees C had an onset temperature of melting at 34.9 degrees C, which was approximately 10 degrees C lower than that observed for the gel hydrated at 23 degrees C. The enthalpy value was greater for the gel hydrated at 4 degrees C (14.2 J/g) than the gel hydrated at 23 degrees C (8.8 J/g). The yield stress and consistency of the hydrogels were proportional to the solid concentration. The hydrogel prepared with 30% retrograded starch powders at 4 degrees C displayed a thick creamy texture with retrograded starch crystals that could melt at a temperature range of 35-51 degrees C. The thermal and rheological properties of the hydrogels exhibited the possibility for the retrograded starch powders to be used as fat mimetic in foods.