Pre-Harvest Foliar Application of Chitooligosaccharide Modulates Aroma Quality of Cabernet Gernischt Wines

Pre-harvest foliar application of chitooligosaccharide (COS) was evaluated for its impact on the flavor quality of Cabernet Gernischt wines. COS was applied at the young berry (YB) and early veraison (EV) stages across the 2022 and 2023 vintages. Physicochemical parameters, phenolic compounds, color index, volatile composition, and sensory quality were systematically analyzed. In 2022, alcohol content and total acidity increased in both treatment groups, total phenols increased in the EV group but decreased in the YB group. In 2023, alcohol and acidity showed opposite trends between the two treatment groups, while phenolic compounds decreased. COS treatment increased wine lightness and yellow tone but reduced red tone and color saturation. In 2022 vintage, YB treatment increased total volatiles with 8.18% and terpenoids with 138.91%, while esters increasing by 34.72-53.60%. In 2023 vintage, total volatiles decreased by approximately 15%, with esters significantly decreasing by 26.60% (YB) and alcohols by 25.96% (EV), while fatty acids increased by 32.70% (EV). OPLS-DA identified key aroma compounds, including phenethyl acetate, ethyl caprate, heptyl acetate, and isoamyl acetate. Aroma wheel analysis showed that fruity and floral notes were enhanced in 2022 but reduced in 2023, with the EV stage consistently performing better. Overall, COS application at the early veraison stage represents a promising strategy for modulating wine flavor quality.