Interactions of digestive enzymes and milk proteins with tea catechins at gastric and intestinal pH

The interactions of digestive enzymes (pepsin, pancreatin) and milk proteins (β‐casein, β‐lactoglobulin (β‐Lg)) with (?)‐epigallocatechin gallate (EGCG), (?)‐epigallocatechin (EGC) and (?)‐epicatechin (EC) at gastric and intestinal pH were investigated by fluorescence spectroscopy. The results indicated that in the gastric environment, all three tea catechins showed binding affinities in descending order of strength with β‐casein first, followed by β‐Lg and then pepsin. The highest affinity was observed for EGCG–β‐casein, with a binding constant (K_A) of 2.502(±0.201) × 10⁵ m ^?1. In the intestinal environment, the binding strengths of the proteins with EGCG and EGC were in the order β‐Lg > pancreatin > β‐casein; for binding with EC, the strength order was β‐casein > β‐Lg > pancreatin. The combination EGCG–β‐Lg had the strongest binding affinity, with a K_A of 14.300(±0.997) × 10⁵ m ^?1. Thermodynamic analysis revealed that tea catechins complexed with milk proteins and digestive enzymes via different hydrophilic and hydrophobic interactions depending on the different digestion environments and types of catechins, proteins and enzymes.