Controlled Sorption Studies of Sprayable Films As Barriers to Smoke-Derived Volatile Phenols in Wine Grapes

Wildfire events have emerged as a persistent threat to viticulture worldwide, creating an urgent need for effective mitigation and preventative practices. This study investigated the use of spray coatings onto grape surfaces to form a physical barrier against smoke-derived volatile phenols. The four film formulations compared included cellulose nanofiber, β-cyclodextrin, chitosan, and a mix of β-cyclodextrin and chitosan. The effectiveness of these films in reducing volatile phenol uptake was evaluated during controlled laboratory sorption experiments. Results revealed significant differences in film performance (p < 0.05), with the chitosan formulation showing the greatest efficacy. In diffusion tests, guaiacol penetration through the chitosan film measured 4.1 × 10⁶ a.u. compared to 3.9 × 10⁷ a.u. for the β-cyclodextrin film. Syringol and m-cresol followed similar patterns: <300 vs 1.6 × 10⁵ a.u. for syringol and 9.7 × 10⁴ vs 3.2 × 10⁷ a.u. for m-cresol (chitosan vs β-cyclodextrin, respectively). These volatile phenols showed consistent film interaction trends across additional sorption experiments, though their uptake varied by concentration. Overall, these findings highlight the potential of sprayable coatings, particularly chitosan-based formulations, as a practical vineyard-level strategy to prevent smoke taint in wine grapes.