Modulating the Photostability of (E)-Resveratrol in Grape Cane Extract Formulations

Pharmaceutical, cosmetic, and agricultural applications of bioactive stilbenoids are limited due to their poor photostability. We aimed to modulate the photostability of (E)-resveratrol in grape cane extract formulations by supplementation with selected additives and monitoring (E)- and (Z)-resveratrol concentrations by HPLC-DAD during 4 h of exposure to artificial sunlight. (E)-Resveratrol in liquid formulations degraded to ca. 13% (0.005 mmol/L) of its initial content (0.040 mmol/L) during the aforementioned illumination (reaction constant k = 0.54 1/h). Deceleration of (E)-resveratrol light-decay was most pronounced when supplemented with dispersible zinc oxide (k = 0.11) or a phenolic apple extract (k = 0.16). In the dried thin-film state, phenolic apple extract (k = 0.08) and zinc oxide (k = 0.12) significantly enhanced the photostability of (E)-resveratrol (control: k = 0.19). Overall, (Z)-resveratrol development was less pronounced than (E)-resveratrol decay, indicating reactions beyond E/Z-isomerization. Briefly, the addition of apple polyphenols or zinc oxide at appropriate dosages was shown to significantly enhance the photostability of (E)-resveratrol in grape cane extract formulations.