Effects of protein oxidation induced by rice bran rancidity on the structure and functionality of rice bran glutelin

Rice bran is the primary by-products of rice milling, and presents high nutritional values. However, the unavoidable occurrence of rice bran rancidity will cause protein oxidation, and impact the protein structure and functionality. The aim of this study is to evaluate the changes in oxidation parameters, structure and functionality of rice bran glutelin during rice bran rancidity. The results indicated the prolongation of rice bran storage time caused the formation of carbonyl groups (from 2.31 to 19.50 nmol/mg) and the loss of sulfhydryl groups (free sulfhydryl groups from 7.66 to 2.16 nmol/mg, and total sulfhydryl groups from 54.88 to 38.76 nmol/mg). The increasing storage time also strengthened the aggregation and cross-linking of rice bran glutelin. The FT-IR spectra implied rice bran rancidity led glutelin to form more complex secondary structure. As rice bran was stored for 1 day, the solubility, water holding capacity, emulsion stability and foam stability raised, and then decreased with the storage time further prolonged. The correlation analysis showed the oxidation parameters, the alpha-helix/beta-sheet ratio and surface hydrophobicity were significantly correlated to the functionality of rice bran glutelin.