Mitigation of malondialdehyde-induced protein lipoxidation by epicatechin in whey protein isolate.

Malondialdehyde (MDA) can induce lipoxidation in whey protein isolate (WPI). The physicochemical changes in this reaction with or without the presence of a phenolic compound epicatechin (EC) were characterized in this study. Results suggested the content of MDA was significantly reduced during co-incubation of MDA and EC. The addition of EC dose-dependently alleviated MDA-induced protein carbonylation, Schiff base formation and loss of tryptophan fluorescence. The interruption of MDA-binding to WPI was directly visualized by immunoblotting analysis. Observation of the surface microstructure of WPI showed that MDA-induced protein aggregation was partially restored by EC. Meanwhile, EC was found to promote loss of both protein sulfhydryls and surface hydrophobicity due to possible phenol-protein interactions. These observations suggested the potential of EC in the relief of MDA-mediated protein lipoxidation.

Epicatechin Inhibited Lipid Oxidation and Protein Lipoxidation in a Fish Oil-Fortified Dairy Mimicking System.

In this study, a typical tea polyphenol epicatechin (EC) was investigated for its impact on the oxidative stability of whey protein isolate (WPI) in a fish oil-fortified emulsion. The oil-in-water emulsion system consisted of fish oil (1%, w/w), WPI (6 mg/mL), and EC (0.1, 1, and 2 mM), and the oxidation reaction was catalyzed by Fenton's reagent at 25 °C for 24 h. The results showed EC exhibited a dose-dependent activity in the reduction of lipid oxidation (TBARS) and protein carbonylation. A Western blot analysis demonstrated that protein lipoxidation was inhibited by EC via interrupting the covalent binding of lipid secondary oxidation products, MDA, onto proteins. In addition, protein lipoxidation induced a loss of tryptophan fluorescence, and protein hydrolysis was partially recovered by EC. The findings of this study provide an in-depth understanding of the performance of phenolic antioxidants in relieving lipid oxidation and subsequent protein lipoxidation in oil-containing dairy products.

Effects of resveratrol on lipid and protein co-oxidation in fish oil-enriched whey protein isolate emulsions.

In this study, the impact of resveratrol (RES) on co-oxidation of lipid and protein in a fish oil-fortified whey protein isolate (WPI) emulsion was investigated. Oil-in-water (O/W) emulsions containing 1% fish oil, 6 mg/mL of WPI and RES (0.08 ~ 2 mM) were oxidatively stressed using a Fenton system at 25 °C for 24 h. The incorporation of RES significantly suppressed lipid oxidation (TBARS) and protein carbonylation. Oxidation-induced decrease on protein sulfhydryl content and surface hydrophobicity were partially attenuated by RES, but protein tryptophan fluorescence was further decreased with the increased concentration of RES. Visualization of protein patterns and MDA-bound protein suggested that RES is capable of inhibiting protein modification induced by secondary products of lipid oxidation. Significant decrease in protein digestibility under oxidizing condition was also mitigated by RES. Our study contributes to the exploration of complicated interactions between oxidized lipids and proteins when phenolic compounds are present.