Effect of Electron Beam Irradiation on the Physicochemical and Structural Properties of Brown Rice Protein Isolates

Electron beam irradiation (EBI) is used to treat cereals, but its effects on isolated proteins recovered after irradiation of intact paddy rice remain unclear. EBI of rice before protein extraction may affect the properties of the recovered protein fraction. Paddy rice from Zhongzao 39 (ZZ39) and Jia 67 (J67) was exposed to 0–20 kGy EBI before dehulling and alkaline protein extraction. Brown rice color and moisture were measured, and the resulting brown rice protein isolates (BRPIs) were characterized using physicochemical, microscopic, spectroscopic, and thermal methods. Grain color varied across treatments, whereas moisture values remained within a narrow range for each rice material. Aqueous protein solubility at pH 7.0 was low and generally decreased after irradiation. Hydrodynamic diameter and surface hydrophobicity showed patterns with variations across the tested dose levels, while the major reducing SDS-PAGE band positions were retained. Fitted amide I profiles, fluorescence intensities, and thermal-transition parameters also differed among treatments. These observations characterize proteins recovered after grain irradiation and subsequent extraction, precipitation, and freeze-drying. The two rice materials showed different descriptive response patterns. Overall, the findings identify changes that should be considered when recovering proteins from irradiated rice. EBI altered BRPI association and conformation without detectable shifts in surface potential or principal reducible subunit distribution. These findings supported the potential of EBI as a physical treatment for modulating brown-rice protein properties, provided that irradiation conditions are selected according to cultivar and the target quality attribute.