Exploratory Characterization of Grape Juice Fortified with Vitis vinifera Leaf Extract: A Proof-of-Concept Study

The increasing demand for sustainable and phytochemically enriched foods has encouraged the valorization of agricultural by-products as ingredients for beverage formulation. This study investigated the enrichment of grape juice with Vitis vinifera leaf extract and characterized the resulting phytochemical, antioxidant, volatile, and sensory profiles. The fortified juice was compared with non-enriched grape juice and a commercial sample. Samples were analyzed at production (t0) and after 30 days of refrigerated storage (4 °C) for polyphenols, flavonoids, anthocyanins, carotenoids, tocopherols, and antioxidant capacity (ABTS, DPPH, and CUPRAC assays). Volatile organic compounds (VOCs), sensory properties, and microbiological stability were also evaluated. The fortified preparation showed higher concentrations of polyphenols, flavonoids, and anthocyanins than the non-fortified preparation. α-Tocopherol, γ-tocopherol, β-carotene, and lutein were detected exclusively in fortified samples. ABTS and CUPRAC assays showed comparatively high antioxidant activity values in the fortified preparation. Lower concentrations of anthocyanins, carotenoids, and tocopherols were observed at t30 than at t0, although substantial levels remained detectable after 30 days. HS-SPME/GC-MS detected 63 VOCs, with the fortified beverage showing a distinct volatile profile after 30 days of refrigerated storage, including comparatively high analytical responses for several monoterpenes and C6 alcohols. Sensory analysis revealed a distinctive profile characterized by greater sourness, bitterness, astringency, density, and aromatic complexity, together with lower overall sensory quality. Microbial counts remained below the respective detection limits under the investigated conditions. Overall, the investigated fortified preparation was characterized by a phytochemically enriched profile and by differences in antioxidant capacity, volatile composition, and sensory characteristics compared with the non-fortified preparation. These findings provide preliminary evidence of the compositional potential of grapevine leaf extract as an ingredient for phytochemically enriched grape-based beverages, while also identifying sensory constraints requiring formulation optimization.