Interaction of epigallocatechin-3-gallate with β-lactoglobulin: molecular characterization and biological implication

Epigallocatechin-3-gallate (EGCG), an antioxidant present in green tea, could play an important role in the prevention of cancer. However, its bioavailability is low due to its instability in gastrointestinal environment. beta-Lactoglobulin (beta-Lg), the major protein in whey, is known for its capacity to bind bioactive molecules and could protect them from oxidation. Interaction between beta-Lg and EGCG was investigated at pH 7.0 and 4.0 using fluorescence and Fourier transform infrared spectroscopy, and its impact on EGCG antioxidant activity was determined using the ferric-reducing antioxidant power method. EGCG bound to native or heat-denatured beta-Lg by hydrogen bonding and possibly hydrophobic interaction at pH 7.0 and 4.0. The affinity of EGCG for heat-denatured beta-Lg at pH 7.0 was greater than for native beta-Lg and greater than its affinity for the protein in either state at pH 4.0. Complexing with beta-Lg decreased the antioxidant activity of EGCG under all conditions investigated. However, the protein provided limited protection of EGCG against degradation over time, the heat-denatured form being slightly more effective at pH 7.0. This study provides insight into the characteristics of beta-Lg binding with a flavonoid and its impact on the antioxidant activity of flavonoids in food systems.