Effect of lipoxygenase-catalyzed oxidation of linoleic acid on the molecular structure and gelation properties (e.g., strength, water-holding capacity) of wheat germ protein

Wheat germ protein (WGP) was incubated with lipoxygenase and linoleic acid to investigate the effect of oxidation on the structure and gelling properties of WGP. Results showed that lipid oxidation induced oxidation of WGP, indicated by increasing of carbonyl group, decrease of free sulfhydryl groups, disulfide bonds and total sulfhydryl groups of WGP. After oxidation, protein solubility increased and zeta-potential decreased. Surface hydrophobicity and the average particle size of WGP first decreased and then increased, suggested that moderate oxidation induced the degradation of original WGP aggregates while excess oxidation promoted the formation of larger aggregates. Oxidative modification induced the unfolding of WGP and further aggregation of WGP through different covalent bonds. For gelling properties, moderate oxidation enhanced the hardness, water-holding capacity and stability of WGP gels, while excessive oxidation decreased the properties of WGP gel, which is probably associated with hydrophobic interaction and disulfide bond.