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.