pH- and ionic strength-dependent interaction between cyanidin-3-O-glucoside and sodium caseinate

•Cyanidin-3-O-glucoside (C3G) interacts with sodium caseinate nanoparticles (NaCas)•Two distinct sets of C3G binding sites on NaCas were evidenced at pH 2 and 7.•Hydrophobic effects predominate at pH 2 against electrostatic interactions at pH 7.•Increasing ionic strength affects differently the two sets of binding sites at pH 7.•Upon complexation, C3G induces a 20% increase of NaCas hyrodynamic diameter. Understanding the mechanism of interaction between food proteins and bioactives constitutes the preliminary step to design food grade nanocarriers. We investigated the interaction between cyanidin-3-O-glucoside (C3G), and 20nm-sized sodium caseinate nanoparticles (NaCas) at pH 7 and pH 2 by fluorescence spectroscopy and dynamic light scattering. The characterization of the C3G-NaCas interaction indicated that the fluorescence quenching mechanism was predominantly static. C3G interacted with two sets of binding sites with association constants Ka of 106 and 105M−1. Electrostatic interactions dominated at pH 7, while hydrophobic effects were the main force at pH 2. Interestingly, the two sets of binding sites were discriminated by ionic strength at pH 7. The binding of C3G slightly modified the average diameter of NaCas nanoparticles without alteration of its surface charge suggesting a complexation of C3G molecules in the internal casein structure. Thus, NaCas constitutes a putative nanocarrier for anthocyanins in new functional foods.