Adsorption of flavonoids on resins: Cyanidin 3-glucoside

Adsorption of cyanidin-3-glucoside in aqueous batch solutions was studied at pH 3.5 and 20 degreesC using 13 commercial resins with different hydrophobicity, surface areas (S-A, 330-1200 m(2)/g), and pore radii (P-R, 20-260 Angstrom). The solute affinity toward different resins was described in terms of Langmuir and Freundlich parameters; experimental data were well-fitted to the two isotherms, which were both utilized to compare resins adsorption capacity. The styrene-divinylbenzene EXA-118 resin (S-A, 1200 m(2)/g; P-R, 90 Angstrom) showed the maximum effectiveness among the tested resins; a good efficacy for removing cyanidin 3-glucoside was shown also by EXA-90 (S-A, 630 m(2)/g; P-R, 105 Angstrom). Some experiments on a styrene-divinylbenzene resin and an acrylic one demonstrated that adsorption was not influenced by pH variations of the solution within the range of 1.0-4.5. For the 10 resins having P-R less than or equal to 105 Angstrom, correlation analysis evidenced the linear increasing dependence of Freundlich constant K-F on physical characteristics of surface area and pore radius. The adsorption of cyanidin 3-glucoside at 20 degreesC was compared with that of hesperidin performed in batch runs on the same resins. Moreover, the best resin (EXA-118) was tested with a sample of pigmented orange juice to assess its performance in terms of selectivity, adsorption, and desorption capabilities on a real matrix.