Iron decreases the antioxidant capacity of red wine under conditions of in vitro digestion

The hypothesis that iron and phenolics interact in the lumen during digestion and, consequently, decrease the antioxidant capacity of phenolics, was investigated in vitro. Mixtures of red wine, iron, and three dietary factors that may reduce or chelate iron in the lumen, namely ascorbic acid, meat and casein, were subjected to a simulated gastrointestinal digestion. The process involved incubation of samples for 4.5 h at 37 °C, at different pHs, in the presence of peptic enzymes and fractionation of digests through a dialysis membrane. Antioxidant capacity (FRAP assay), iron concentration (ferrozine assay) and total phenolic content (Folin-Ciocalteau assay) were measured in the in vitro digests. Iron decreased the antioxidant capacity and the total phenolic concentration of red wine. Ascorbic acid increased, while meat and casein decreased, the antioxidant capacity of red wine. Based on these results, it was concluded that protein and iron interact with red wine phenolics during the in vitro digestion and decrease their antioxidant capacity, supporting the initial hypothesis.