trans-Resveratrol and ε-viniferin recovery from grapevine pruning residues: process optimization and varietal screening towards industrial valorisation

Abstract Vine shoots are abundant viticultural by-products and promising renewable sources of high value stilbenoids for sustainable biorefinery applications. Stilbenoids are phytoalexins bearing phenolic moieties produced by Vitaceae under biotic and abiotic stress, and endowed with nutraceutical, cosmeceutical, and agrochemical potential. This study optimized the recovery of trans -resveratrol and ε-viniferin from vine shoots using Box–Behnken response surface methodology by evaluating extraction time (t), solvent mixture (S), and matrix-to-solvent ratio (R) as initial step of the circular economy task of European LIFE - Natural Agro project. The optimized conditions were then applied to conventional solid–liquid extraction (SLE), ultrasound-assisted extraction (UAE), and Soxhlet extraction. The optimal conditions were 100% ethanol, R = 0.12 g mL⁻¹, and t = 35 min. Although Soxhlet extraction gave the highest extraction yield (EY%), UAE produced the most stilbene-enriched extract, with 9.50 mg g⁻¹ dry extract of trans -resveratrol and 25.66 mg g⁻¹ dry extract of ε-viniferin, while reducing extraction time and prolonged thermal exposure. The optimized UAE protocol was subsequently applied to grapevine varieties from Italy, Portugal, and France, revealing marked genotype-dependent differences in stilbene composition. ε-Viniferin was generally more abundant than trans -resveratrol, and Pinot Meunier, Grechetto Gentile, Moscato, and Moscatel Graudo were identified as promising raw materials, depending on the target compound. Spectrophotometric assays further confirmed variety-dependent differences in antioxidant activity, total phenolic content, and total flavonoid content. Overall, the proposed UAE strategy offers a simple, food-grade, and scalable approach for valorising vine-pruning residues as sources of bioactive ingredients.