Effects of oxidative modification by 13-hydroperoxyoctadecadienoic acid on the structure and functional properties of rice protein.

13-hydroperoxyoctadecadienoic acid (13-HPODE) was selected as lipid peroxidation primary products during rice ageing to investigate the effects of lipid hydroperoxide modification on the structural characteristics and functional properties of rice protein. Incubation of rice protein with 13-HPODE resulted in protein carbonylation and loss of protein sulfhydryl groups in a concentration-dependent manner. FT-IR evaluated the effects of 13-HPODE on rice protein, and the results indicated increasing concentration of 13-HPODE resulted in continuous loss of α-helix, β-turn and random coil structure, and increase in β-sheet content and amino acid side chains. The content of soluble protein aggregates gradually increased, accompanied by protein crosslink via disulfide bonds. 13-HPODE had a negative impact on the solubility, water holding capacity, foaming capacity, and foam stability of rice protein. 13-HPODE could promote oil holding capacity of rice protein. With the concentration of 13-HPODE below 0.1 mmol/L, emulsifying activity index (EAI) and emulsifying stability index (ESI) of rice protein gradually increased, which due to gradual increase in rice protein surface hydrophobicity and flexibility. However, at relatively high concentration of 13-HPODE (above 1 mmol/L), the adverse effect in EAI and ESI was observed, which might be attributed to a decrease in surface hydrophobicity and protein aggregates formation.