Interaction of anthocyanins with human serum albumin: Influence of pH and chemical structure on binding

The affinity of anthocyanins for human serum albumin (HSA) was determined by a fluorescence quenching method. The effects of pH and structure of anthocyanins on the binding constants were studied. The constants for binding of anthocyanins to HSA ranged from 1.08 × 105 to 13.2 × 105 M−1. A hydrophobic effect at acidic pH was shown by the relatively high positive entropy values under the conditions studied. Electrostatic interactions, including hydrogen bonding, contributed to the binding at pH 7.4. The effect of structure of anthocyanins on the affinity was pH-dependent, particularly the effect of additional hydroxyl substituents. Hydroxyl substituents and glycosylation of anthocyanins decreased the affinity for binding to HSA at lower pH (especially pH 4), but increased the strength of binding at pH 7.4. In contrast, methylation of a hydroxyl group enhanced the binding at acidic pH, whilst this substitution reduced the strength of binding at pH 7.4. This paper shows that changes in anthocyanin structure or reductions in pH, which may occur in the region of inflammatory sites, have an effect on the binding of anthocyanins to HSA.