Impacts of lipid oxidation product malondialdehyde (MDA) on the properties of whey protein isolate (WPI) were investigated in this study. The incorporation of MDA into WPI promoted the formation of protein carbonyls, with the significant loss of protein sulfhydryls, impaired intrinsic fluorescence, and increased protein surface hydrophobicity. The visualized band profiles revealed by gel electrophoresis and immunoblotting suggested that WPI’s main components β‐lactoglobulin and α‐lactalbumin were the targets of MDA, and the derivatives of MDA were involved in protein cross‐linking and aggregation at higher molecular weights. Abnormal protein aggregation was further confirmed by scanning electron microscopy analysis of the surface microstructure of MDA‐modified WPI. Finally, in vitro digestibility assay indicated that the modification of MDA reduced WPI’s susceptibility to digestive enzymes. The present study demonstrated that the contribution of MDA to protein modification in dairy products can be substantial in complex foodstuffs composed of lipids and proteins. Practical applications The present work enhanced our knowledge on the remarkable susceptibility of dairy product WPI to lipid oxidation product MDA. With the trend of application of highly unsaturated fatty acids such as fish oil or alga oils as functional ingredients in dairy products, it is obvious that apart from monitoring lipid oxidation products, the resultant changes in dietary proteins deserve more attention. The food industry must be aware of the importance of appropriate preventive measures in minimizing the negative effects of lipid oxidation products on dairy products.

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BACKGROUND: The influence of epicatechin (EC) on the physicochemical properties and digestibility changes of porcine myofibrillar protein (MP) under oxidative stress during refrigerated storage was investigated. RESULTS: The incubation of MP suspensions (20 mg mL −1 in piperazine-N,N 0-bis(2-ethanesulfonic acid) buffer, with 0.6 mol L −1 sodium chloride, pH 6.25) at 4°C for 24 h under an iron-catalyzed hydroxyl radical generating system (Fenton reaction) promoted the formation of thiobarbituric acid reactive substances and protein carbonyls, which was attenuated by EC (5, 50, and 100 ∼mol g −1 protein). Reduced protein sulfhydryl content, tryptophan fluorescence, protein solubility, as well as increased surface hydrophobicity were found by the co-incubation of EC. Analysis by scanning electron microscopy revealed increased protein aggregation and fragments in oxidized MP, which were further enhanced by the addition of EC. However, the protein digestibility of MP was not affected. CONCLUSION: EC was demonstrated to be effective in alleviating lipid oxidation and protein carbonylation in MP under oxidative stress. Additionally, the physicochemical and digestibility changes accompanying the incorporation of EC was complicated due to the possible phenol-protein interactions. An in-depth understanding of protein physicochemical and digestibility changes will be helpful in the application of polyphenolic compounds as antioxidants in low-temperature-processed muscle foods.