Ca-promoted free radical grafting of whey protein to EGCG: As a novel nanocarrier for the encapsulation of apigenin.

Whey protein (WP) is often used as a delivery carrier due to its superior biological activity and nutritional value. Covalent binding of WP to epigallocatechin gallate (EGCG) can significantly improve the performance of WP in encapsulated materials. Nevertheless, the preparation of WP-EGCG covalent complexes still suffers from low grafting rates. Studies have shown that calcium ions (Ca) can modify the structure of proteins. We therefore explored the effect of calcium chloride (CaCl) on the free radical grafting of EGCG and WP. The experimental results showed that the grafting rate of free radicals increased by 17.89% after adding Ca. Furthermore, the impact of WP-EGCG-Ca covalent complex on the entrapment efficiency of apigenin (AP) was further examined, and the results revealed that the entrapment rate could reach 93.66% at an apigenin concentration of 0.2 mg/mL. Simulated gastrointestinal digestion showed that WP-EGCG-Ca covalent complex could significantly improve the bioavailability of AP. The study provides new ideas to broaden the application of WP as a carrier for delivering bioactive substances.