The effects of gallic acid on the solubility, swelling, gelatinization, and rheological properties of rice starch, and the characteristics of the molecular and crystal structures of gallic acid-starch complexes were investigated. The results demonstrate that gallic acid significantly increased the solubility and reduced the swelling, gelatinization temperature, and gelatinization enthalpy of rice starch (p<0.05). This suggests that gallic acid could inhibit the gelatinization of starch and reduce its thermal stability. Gallic acid decreased the gelatinized viscosity and setback values of the treated rice starch, indicating that gallic acid reduced the cross-linking between the starch chains and inhibited the retrogradation of the rice starch. These gallic acid and rice starch mixtures represent a typical pseudoplastic fluid, and demonstrated the associated shear-thinning characteristics. The addition of gallic acid significantly reduced the storage modulus and loss modulus of starch gels, and the viscoelasticity of gallic acid-starch gel systems. This indicates that gallic acid has a destructive effect on starch gel structure. Infrared spectroscopy showed that the peak intensity ratio of the gallic acid-starch complex, at 1045/1022 cm-1, decreased, suggesting that the addition of gallic acid reduces the order structure of rice starch. In addition, the data suggests that these two products primarily interact via the production of hydrogen bonds. X-ray diffraction demonstrated that these complexes formed a new diffraction peak at 12.7 °, indicating that gallic acid interacts with rice starch to form a unique crystal structure. This study provides theoretical guidance for the application of gallic acid in the improvement of starch-based functional foods.
