Valorization of Shiraz and Tempranillo grape wine by-products: Impact of drying and extraction methods on phytochemical contents and health-promoting activities

Industrial grape wine by-products (GWBs) are typically underutilized as low-value animal feeds or fertilizers despite containing valuable phytochemicals with potential medicinal properties. In Thailand, Shiraz and Tempranillo grape varieties generate substantial GWBs from rosé and red wine production, yet their health-beneficial properties remain poorly characterized. This research evaluated how drying processes (oven-drying versus freeze-drying) and extraction methods (hydroethanolic versus hot water extraction) affect the phenolic profiles, antioxidant capacity, anti-aging properties, and inhibitory activities against key enzymes associated with diabetes, hyperlipidemia, and Alzheimer's disease. Results demonstrated that freeze-drying preserved higher phenolic contents and bioactivities compared to thermal oven-drying, while hydroethanolic extraction proved more effective than hot water extraction. Notably, extraction solvent had a greater influence on phenolic recovery than drying method. GWBs from Shiraz Rosé wine production exhibited superior bioactivities compared to Tempranillo by-products, with distinct phenolic profiles dominated by cyanidin and hydroxybenzoic acid derivatives. This research demonstrates the potential to transform low-value GWBs into valuable bioactive ingredients for functional foods and nutraceutical applications. • Freeze-drying preserved more phenolics in GWBs than oven-drying • Aqueous ethanolic extraction yielded higher TPCs & bioactivities than hot water • Solvent type affected phenolic extraction from GWBs more than drying process • TPCs & bioactivities in Shiraz and Tempranillo GWBs varied by drying and extraction