Competitive interactions among tea catechins, proteins, and digestive enzymes modulate in vitro protein digestibility, catechin bioaccessibility, and antioxidant activity of milk tea beverage model systems

This work aimed to study the effects of the competitive interaction among tea catechins, milk proteins, and digestive enzymes on protein digestibility, catechin bioaccessibility, and antioxidant activity by simulating in vitro digestion. The inhibitory effect of catechins on digestive enzymes was positively correlated with the binding affinity of catechins to digestive enzymes. The interaction between tea catechins and milk proteins or digestive enzymes resulted in the reduction of protein digestibility. The bioaccessibility of catechins and antioxidant activity of the milk tea beverage were reduced by protein-catechin interaction, but they increased via competition among proteins, catechins, and digestive enzymes. After the addition of β-lactoglobulin (β-Lg), epigallocatechin gallate (EGCG), epigallocatechin (EGC), and epicatechin (EC) bioaccessibility increased by 252.6%, 85.0%, and 37.0%, respectively. The addition of β-casein (β-CN) negatively affected EGCG and EGC bioaccessibility but significantly increased EC bioaccessibility. The addition of β-Lg and β-CN showed better protective effects on antioxidant activity. The bioaccessibility of tea catechins mixed with β-Lg is significantly higher than that of tea catechins mixed with β-CN in the gastrointestinal digestion stage, except for the mixture of EC and β-CN. The increase in catechin bioaccessibility and antioxidant activity was positively correlated to the binding affinity of catechins-proteins.