Stabilization of oxidable vitamins by flavonoid-based hydrogels

This study has the goal to evaluate the stability of B complex vitamins, loaded into catechin-based crosslinked hydrogels, in aqueous medium at accelerated conditions of oxidative stress. The formulations were prepared by coupling polyacrylic acid with catechin in the presence of dicycloexylcarbodiimide. Folic acid (FA) and Thiamine (TH) were chosen within the B complex vitamins because of the well-known oxidative degradation characteristics. The protective role of the hydrogels against the oxidation damage was monitored inducing oxidative stress, by means of UV irradiation and t-butyl hydroperoxide treatment for FA and TH, respectively. The characterization of the hydrogels was obtained by morphological, calorimetric, FT-IR analyses, antioxidant assays and evaluation of the swelling behavior in aqueous media at different pH. The experimental results confirmed the suitability of the hydrogels as pH-responsive devices, furthermore the presence of oxidative condition proved the protective effect of the hydrogels. Catechin-based polymers gave a pronounced improvement in the stability of vitamins compared to hydrogels prepared by the coupling reaction of polyacrylic acid in the presence of 1,6-hexandiol. Under oxidative conditions, FA and TH were preserved by 96% and 60% respectively.