Revolutionizing Wine Waste: Advanced Techniques for Polyphenol Recovery from White Wine Byproducts

This study investigates the recovery of bioactive polyphenolic compounds from the pomace of two white winemaking grape varieties, Moschofilero and Rhoditis. The pomace was subjected to two drying techniques: air drying (AD) and solar drying (SD). Extraction methods included microwave-assisted extraction (MW), ultrasound-assisted extraction (US), and Soxhlet extraction (S), using water and water–ethanol (WE) solvents. Antioxidant activity (IC50), total phenolic content (TPC), and total flavan-3-ol content (TFC) were determined. For Moschofilero, SD pomace extracted with US-WE showed the highest antioxidant activity (IC50: 0.59 mg/mL) and the highest phenolic recovery (TPC: 285.76 mg gallic acid equivalents (GAE)/g) and flavan-3-ol content (TFC: 46.21 mg catechin equivalents (CE)/g). For Rhoditis, AD pomace extracted with US-WE demonstrated superior antioxidant activity (IC50: 1.08 mg/mL), phenolic content (TPC: 216.51 mg GAE/g), and flavan-3-ol content (TFC: 35.96 mg CE/g). HPLC analysis identified quercetin-3-glucuronide, myricetin, and quercetin as the main flavonols in both grape varieties, with Moschofilero also containing isorhamnetin-3-glucoside and syringetin-3-glucoside. Drying and extraction methods significantly influenced the recovery of bioactive compounds, with US combined with AD or SD yielding the best results for both grape varieties These findings show that improved drying and extraction methods can add value to grape pomace for use in functional foods and nutraceuticals.