Whey protein and phenolic compound complexation: Effects on antioxidant capacity before and after in vitro digestion

Whey protein isolate (WPI) interactions with (-)-epigallocatechin gallate (EGCG) and caffeic acid (CA) at pH 3.5 and 7.0 were investigated concerning complex formation and antioxidant capacity, before and after simulated digestion. Complex formation was evidenced by protein structural changes when WPI was associated with CA or EGCG. Reducing capacity and FRAP values increased as the phenolic compound concentration increased while ORAC values remained unchanged. In general, compared to the isolated compounds, complexation suppressed the antioxidant capacity possibly due to hydrophobic interaction and H-bonding between these compounds. Protein:phenolic complexation in 1:0.5 M ratio did not affect the digestibility compared to WPI (83%), except for WPI:CA at pH 7.0 (73%). The hydrophilicity profile of the digested samples suggested that pH of complexation and type of phenolic affected the protein cleavage pattern. Furthermore, the phenolic compounds were more stable when associated with the protein since they were protected from the simulated gastrointestinal environment.