Sustainable Extraction and Purification of Trans-Resveratrol from Grape Pomace: Valorization of a Winemaking By-Product

Grape pomace, the main solid by-product of winemaking, is a promising feedstock for the recovery of trans-resveratrol, a high-value stilbene of increasing interest for food, nutraceutical, and pharmaceutical applications. However, its efficient isolation remains challenging because of matrix complexity, the co-occurrence of structurally related stilbenes and polyphenols, and the chemical instability of trans-resveratrol. This review critically examines recent advances in the recovery of trans-resveratrol from grape pomace, while also incorporating relevant findings from other grapevine-derived matrices to distinguish matrix-specific recovery potential and to place grape pomace within the broader context of grapevine by-product valorization from extraction intensification and selective purification to analytical determination. Various extraction technologies, including ultrasound-, microwave-, and enzyme-assisted extraction, natural deep eutectic solvents, and subcritical water extraction, are assessed alongside conventional solvent extraction with emphasis on yield, selectivity, solvent compatibility, and process feasibility. Downstream separation methods such as liquid–liquid partitioning, solid-phase isolation, adsorbent resins, counter-current chromatography, molecularly imprinted polymers, and foam fractionation are compared in terms of selectivity, enrichment efficiency, solvent demand, and scale-up potential. Although significant progress has been achieved, major challenges remain regarding process integration, solvent sustainability, product stability, and industrial feasibility. Combining mild extraction with selective downstream purification is essential for producing stable, high-purity trans-resveratrol fractions suitable for future use in functional ingredients, natural preservation strategies, and other value-added applications within sustainable food systems.