Effect of Phenolic Compounds on the Formation of α-Aminoadipic and γ-Glutamic Semialdehydes from Myofibrillar Proteins Oxidized by Copper, Iron, and Myoglobin

The effect of selected phenolic compounds, namely, gallic acid, chlorogenic acid, genistein, catechin, cyanidin-3-glucoside and rutin, on the formation of specific protein carbonyls, α-aminoadipic and γ-glutamic semialdehydes (AAS and GGS, respectively), from oxidized myofibrillar proteins, was studied in the present article. Suspensions containing myofibrillar proteins (20 mg/mL) and the aforementioned phenolic compounds (1 mM) were oxidized (37 °C for 20 days) in the presence of copper acetate, iron (FeCl3), or myoglobin (10 μM) in combination with 1 mM H2O2 and analyzed for AAS and GGS using liquid chromatography−electrospray ionization−mass spectrometry (LC-ESI-MS). Suspensions with added α-tocopherol (1 mM) and a control group (with no phenolic compound) were also considered. In the presence of copper, the α-tocopherol and most phenolic compounds significantly inhibited the formation of AAS and GGS. In iron- and myoglobin-oxidized suspensions, however, some of those phenolic compounds (i.e., chlorogenic acid and genistein) promoted the formation of the semialdehydes. Besides the influence of the oxidation promoters, the overall effect of plant phenolics on protein oxidation is likely affected by the chemical structure of the phenolics and the result of the interactions between these compounds and myofibrillar proteins. Plausible mechanisms for the antioxidant and pro-oxidant effects of plant phenolics on myofibrillar proteins are proposed in the present article. This study highlights the complexity of redox reactions between plant phenolics and oxidizing myofibrillar proteins.