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 °C using 13 commercial resins with different hydrophobicity, surface areas (S A, 330−1200 m2/g), and pore radii (P R, 20−260 Å). 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 m2/g; P R, 90 Å) 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 m2/g; P R, 105 Å). 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 ≤ 105 Å, 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 °C 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. Keywords: Acrylic resins; adsorption; anthocyanins; Freundlich isotherm; Langmuir isotherm; styrene−divinylbenzene resins