Effect of γ-Ray Irradiation on Eating Quality of Rice and Physicochemical Properties of Rice Starch

In order to investigate the effects of different doses of ⁶⁰Co-γ-ray irradiation on rice, this experiment employed a texture analyzer, a rapid viscosity analyzer, a differential scanning calorimeter, a rheometer, an X-ray diffractometer, and a Fourier transform infrared spectrometer to characterize the eating quality of rice and the physicochemical properties and structure of rice starch. The results indicated that as irradiation dose increased, the water absorption and volumetric expansion of rice during cooking, and the pH, dissolved solid content and iodine blue value of rice broth fell significantly (P < 0.05). High doses of irradiation resulted in a noticeable increase in the total color difference (ΔE) of rice compared with that before irradiation, and a ΔE of 12.53 was obtained at 10 kGy, indicating a significant color change. Also, the irradiation notably affected the hardness of cooked rice. The peak viscosity, setback value, and gelatinization enthalpy of rice starch decreased significantly (P < 0.05) with the increase in irradiation dose; the irradiation also reduced the rigidity, elasticity, relative crystallinity and orderliness of rice starch, with the crystallinity being decreased from 23.68% to 15.69%. The measurement results of cooking indicators, rice soup properties, ΔE, and texture characteristics indicate that higher irradiation doses reduced the edible quality of rice. Moreover, the contents of slowly digestible starch and resistant starch in irradiated rice starch increased, with the latter being increased to 20.22% after irradiation treatment at 4 kGy. Compared with the unirradiated control, the irradiation reduced the hydrolysis rate of starch. Overall, γ-ray irradiation altered the crystalline structure of starch, thereby enhancing its pasting and rheological properties and inhibiting its digestibility, but rice is not suitable for high doses of irradiation treatment. This study provides theoretical guidance for the production of irradiated rice and its products, as well as for the modification of starch.