Influences of pH on binding mechanisms of anthocyanins from butterfly pea flower (Clitoria ternatea) with whey powder and whey protein isolate

The interactions between whey proteins and delphinidin-based anthocyanins in the water extract of Clitoria ternatea dried flower was investigated by measuring fluorescence quenching of whey powder proteins (WP) and whey protein isolate (WPI) by anthocyanins. Within the temperature range between 35 to 45 degrees C and buffer pH range between 2.5 to 11.0, the binding of whey proteins with anthocyanins in C. ternatea petal was spontaneous and governed by hydrophobic interactions. The formation of the protein-anthocyanin complex was influenced by the pH and non-protein constituents, i.e. lactose and minerals. In addition to hydrophobic interactions, electrostatic interactions played an important role in the complex formation mechanisms of whey proteins in WP with anthocyanins. Nonetheless, the formation of the protein-anthocyanin complex of proteins in WPI did not involve electrostatic interactions. This investigation indicated the influences of non-protein constituents on the protein and anthocyanin microenvironments, which determined the types and binding strength of non-covalent forces involved in the complex formation. This study also suggested the means for tailoring the binding of delphinidin-based anthocyanin with whey protein via non-covalent forces to formulate macromolecular encapsulation of delphinidin-based anthocyanins by altering the composition of non-protein constituents and pH at the temperature below 45 degrees C.