Molecular interaction of cyanidin-3-O-glucoside with ovalbumin: insights from spectroscopic, molecular docking and in vitro digestive studies

Anthocyanins bound with proteins have influence on the digestibility of proteins. In this study, the interaction between cyanidin-3-O-glucoside (C3G) and ovalbumin (OVA) was investigated through multi-spectroscopy and molecular docking. The interactive effect of C3G on OVA digestibility was estimated by an in vitro digestion model. Fluorescence studies indicated that C3G quenched the fluorescence of OVA in a static mode, where the binding constants (Ka) at 298, 308 and 318 K were above 10(5) M-1, indicating a strong binding affinity of C3G with OVA. The negative values of thermodynamic parameters (Delta G, Delta H and Delta S) revealed a spontaneous binding process, where hydrogen and van der Waals forces were involved in stabilizing the OVA-C3G complex. The secondary structure of OVA was modified by C3G binding, with augmented beta-sheet (21.5%-25.1%) and diminished alpha-helix (23.3%-21.6%). Besides, C3G substantially inhibited the digestion of OVA in pancreatin solution whereas it had negligible effect on pepsin. Furthermore, molecular docking and cleavage site prediction studies showed that the hydrogen binding sites of C3G are not near to the cleavage sites of pepsin but partially overlap trypsin cleavages sites in OVA, which might lead to an inhibited effect on pancreatic digestion. These results provide a better understanding of the anthocyanin-protein interactions and their effect on the protein digestibility.