Comparison of the interaction between three anthocyanins and human serum albumins by spectroscopy

Anthocyanin is an important kind of water-soluble pigment existing widely in plants, and has various health benefits to human body. The number and location of the hydroxyl groups of the parent nucleus of Anthocyanins have significant effects on their activities. This research employed different spectroscopic methods (i.e. fluorescence spectroscopy, UV-vis absorbance, three-dimensional fluorescence spectra and circular dichroism (CD)) to investigate the mutual interactions between three differently substituted B-ring hydroxyl groups (Pelargonidin-3-O-glucoside, P3G; Cyanidin-3-O-glucoside, C3G and Delphinidin-3-O-glucoside, D3G) and human serum albumin (HSA) under physiological pH conditions. The calculated thermodynamic parameters and the spectrum showed that P3G, C3G and D3G could result in quenching of the intrinsic fluorescence. The comparison result of the strength of comprehensive binding parameter Y (i.e. Y=lg( Ka×E×n/r)), which was used to reflect the extent of interaction of Anthocyanin-HSA system, was YD3G>YC3G>YP3G. Moreover, the secondary structure of HSA was changed in the presence of P3G/C3G/D3G. The α-helix percentage of P3G-HSA increased while that of C3G/D3G-HSA decreased. Overall, these results showed that the number of B-ring -OH in each molecule played an important role in the interaction of these anthocyanins with HSA.