Impact of different ionic strengths on protein-lipid co-oxidation in whey protein isolate-stabilized oil-in-water emulsions

•Ionic strengths influenced the physical stability of O/W emulsions.•Concentration of adsorbed proteins decreased at higher ionic strengths.•Adsorbed proteins acted as an interfacial barrier to retard lipid oxidation.•Adsorbed proteins were more easily oxidized than unadsorbed proteins.•Protein-lipid co-oxidation was related to the interfacial composition of droplets. Protein-lipid co-oxidation of whey protein isolate (WPI)-stabilized oil-in-water (O/W) emulsions with different ionic strengths (0, 100, 200, 300 and 400 mM) during storage were investigated. The results proved that changes in levels of adsorbed proteins induced by different ionic strengths could obviously affect the occurrence of protein-lipid co-oxidation. The level of oxidative stress was higher in adsorbed proteins extracted from control sample than in those extracted from emulsions with 300 or 400 mM ionic strengths. This was indicated by higher levels of N′-formyl-l-kynurenine (NFK) and carbonyl, lower fluorescence intensity and more serious unfolding of protein structure. Moreover, control sample showed the highest oxidative stability, which was indicated by lower levels of primary and secondary lipid oxidation products. These findings clearly illustrated that altered levels of adsorbed proteins induced by different ionic strengths play a crucial role in affecting protein-lipid co-oxidation in O/W emulsions.