Effect of Phenolic Hydroxyl Group Number on Regulation of the Self-Assembly Behavior of Edible Dock Protein and Catechins

To investigate the effect of phenolic hydroxyl group number on the interaction between catechins and a plant-derived protein carrier, four catechins with varying hydroxyl numbers—epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)—were investigated. The new plant-derived edible dock protein (EDP) was selected as a carrier matrix. EDP, when employed as a protein delivery carrier, possessed a hydrophobic amino acid content of 45%. This structural feature enabled it to provide more hydrophobic cavities for small molecule compounds, thereby facilitating better binding with them. The results indicated that the order of loading capacity of catechins within EDP was EGCG (9.7%) > ECG (9.1%) > EGC (8.8%) > EC (7.1%). This sequence was consistent with the number of hydroxyl groups in catechin: EGCG (8) > ECG (7) > EGC (6) > EC (5). Among the four catechins, EGCG had the highest binding constant (Ka = 2.6 × 103 L/mol), leading to the largest quenching of EDP. During self-assembly, hydrogen bonding, hydrophobic and electrostatic interactions were the main driving forces, and the interaction between EGCG and EDP was the strongest. This study indicated that the hydroxyl group number of polyphenolic compounds can determine its binding affinity with proteins.