Abstract: Effects of oxidative modification by peroxyl radicals derived from oxidative thermal decomposition of 2,2’-azobis(2-amidinopropane) (AAPH) at different concentrations on the structural and functional properties of rice bran protein were investigated. The results indicated that as AAPH concentration increased, protein carbonyl, disulfide, and dityrosine contents of rice bran protein increased from 2.0 nmol/mg, 12.04 nmol/mg, and 84.54 to 7.09 nmol/mg, 14.69 nmol/mg, and 127.1, respectively, while free sulfhydryl content decreased from 23.97 to 15.29 nmol/mg. Oxidative modification by peroxyl radicals resulted in a decrease in α-helix and random coil content and an increase in β-sheet content. Besides, the content of amino acid side chains firstly increased, and then slightly decreased after this treatment, which also led to a decreased in surface hydrophobicity and intrinsic fluorescence intensity accompanied by a blue shift of the maximum emission wavelength. Nevertheless, oxidative modification by peroxyl radicals had no significant impact on the subunit structure of rice bran protein, but caused polypeptide chain aggregation of rice bran protein accompanied by partial rupture of the major polypeptide chain to form peptides. As AAPH concentration increased, rice bran protein solubility gradually decreased; however, water-holding capacity, oil-holding capacity, foaming activity, foaming stability, emulsifying activity, and emulsiong stability firstly increased and then decreased.

Key words: peroxy radicals, rice bran protein, protein oxidation, structure, functional properties