Physical properties of retrogradation of rice gels produced by high shear during refrigerated storage

Rice gel (RG) is produced by applying high shear to cooked high-amylose rice, whereas rice flour gel (RFG) is prepared by gelatinizing a mixture of rice flour and water. Both gels harden during refrigerated storage because of starch retrogradation; however, the retrogradation behavior of RG remains poorly understood. This study compared the retrogradation behavior of RG and RFG using wide-angle X-ray diffraction, differential scanning calorimetry, dynamic viscoelasticity measurements, and compression testing. Both RG and RFG exhibited increased crystallinity and hardness with storage. Dynamic viscoelasticity measurements revealed that RG reached rheological characteristics comparable to those of a true gel after 7 d of storage, whereas RFG required 14-21 d. The results suggest that the onset of detectable starch recrystallization contributes to true gel network formation. These findings provide new insights into the retrogradation behavior of RG and may aid in developing strategies to suppress quality deterioration during refrigerated storage.