Profiling Free and Glycosidically Bound Volatile Compounds of Portuguese Minority Grape Varieties Under Different Irrigation Treatments

In the context of climate change, vineyards are expected to face increasing constraints on water availability, with more frequent and severe drought conditions posing a major challenge to grapevine production. Gaining insight into how water availability affects the volatile profile in autochthonous grape varieties could be a valuable way to assess their ability to adapt to drought conditions. The objective of this study was to investigate the impact of different irrigation treatments (water comfort, moderate water deficit and rainfed) on the volatile composition of Portuguese autochthonous grape varieties, namely Moreto, Tinta Miúda, Tinta Gorda, and Tinta Caiada, in the 2024 harvest. To do that, the free and bound volatile compounds were analyzed by HS-SBSE-GC-MS. Free volatiles were highest under water comfort in Moreto and under rainfed conditions in Tinta Miúda, whereas Tinta Gorda and Tinta Caiada showed limited variation in total free volatiles across regimes. Bound volatiles responded differently, reaching their highest levels under moderate water deficit in Tinta Gorda and Tinta Caiada, while Tinta Miúda showed higher bound levels under water comfort. Overall, octanoic acid, 2-hexenal, vanillin and citronellal dominated the free fraction, whereas the bound fraction was characterized mainly by β-ionol and benzyl alcohol. Overall, during the 2024 harvest, Tinta Gorda and Tinta Caiada showed slight differences in total free-volatile concentrations across irrigation treatments.