Effect of bovine serum albumin on gallic acid and tannic acid radical scavenging properties and binding kinetics with 2,2-diphenyl-1-picrylhydrazyl

A detailed study on gallic acid (GA), tannic acid (TA) antioxidant properties, and binding kinetics with 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) in the presence of bovine serum albumin (BSA) was performed using electronic absorption, fluorescence, and FTIR spectroscopy methods. The effective concentration (EC50), antioxidant reducing power (ARP), stoichiometry (EC100), and the number of reduced DPPH˙(n) were determined using the DPPH˙ assay. It was shown that the antioxidant effect of GA/TA slightly reduces in the presence of BSA, but the duration of the antioxidant action of GA/TA increases due to the complex formation with BSA. The concentration of free and BSA-bounded GA/TA was determined by fluorescence spectra. The rate constant (kobs), which describes the main reaction between antioxidant and DPPH˙, and the second-order rate constant (k2) were determined. FTIR studies showed that the binding of GA/TA to BSA causes conformational changes in the secondary structure of the protein (decrease of α-helixes, an increase of β-sheet structures). Moreover, TA induces more pronounced effects compared to GA.