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 (UV/Vis), fluorescence, and Fourier transform infrared (FTIR), spectroscopy methods. The effective concentration (EC 50 ), antioxidant reducing power (ARP), stoichiometry (EC 100 ), and the number of reduced DPPH˙ (n) were determined using the DPPH ˙ assay. It was shown that the antioxidant efficacy of GA/TA reduces slightly in the presence of BSA. However, the duration of the antioxidant activity of GA/TA increases as a result of the complex formation with BSA. The concentration of free and BSA-bound GA/TA was determined using fluorescence spectra. The rate constant ( k obs ), which describes the main reaction between antioxidant and DPPH ˙, and the second-order rate constant ( k 2 ) were determined. FTIR studies showed that the binding of GA/TA with 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.