Antioxidant and pro-oxidant activity of (−)-epigallocatechin-3-gallate in food emulsions: Influence of pH and phenolic concentration

Polyphenols have been observed to exert both antioxidant and pro-oxidant activity in lipid foods, and factors that influence that net effect include both polyphenol concentration and matrix pH. In this study, the effects of concentration (1–500 μM) of a model polyphenol, (−)-epigallocatechin-3-gallate (EGCG), and matrix pH (2–7) on the net anti-/pro-oxidant activity of EGCG in flaxseed oil-in-water (o/w) emulsions were systematically evaluated. After 24 h, EGCG (5–100 μM) was observed to exhibit pro-oxidant activity in low pH (pH 2–4) emulsions, as determined by conjugated dienes (CDs) and thiobarbituric acid reactive substances (TBARSs) production. At the higher pH values studied (pH 5–7), lower CD and TBARS concentrations were detected in samples with 25–500 μM EGCG at 24 h. Overall, EGCG concentration and pH both played significant roles in determining net antioxidant or pro-oxidant effects, with the largest antioxidant and pro-oxidant effects observed at the higher EGCG concentrations (100–500 μM) tested.