GREEN VALORIZATION OF VITICULTURE WASTE: OPTIMIZATION OF ULTRASOUND-ASSISTED EXTRACTION OF TRANS-RESVERATROL FROM VITIS VINIFERA CV. SULTANINA POMACE USING RESPONSE SURFACE METHODOLOGY AND EVALUATION OF ITS ANTIOXIDANT ACTIVITY

Abstract

The wine and grape-processing industries generate large volumes of organic waste rich in bioactive compounds, particularly trans-resveratrol, a stilbene with potent antioxidant and pharmacological properties. The present study reports the development and optimization of an eco-friendly ultrasound-assisted extraction (UAE) protocol for the recovery of trans-resveratrol from Vitis vinifera cv. Sultanina pomace sourced from Jhang Baazar, Faisalabad, Pakistan. Three green techniques, UAE, microwave-assisted extraction (MAE) and enzyme-assisted extraction (EAE), were initially compared under fixed conditions, and UAE produced the highest yield (2.86 mg/g dry weight). Response Surface Methodology (RSM) using a central composite design (30 runs) was then employed to optimize four variables: ethanol concentration (40–80%), temperature (30–70 °C), time (10–50 min) and solid-to-solvent ratio (1:10–1:40 w/v). The fitted quadratic model was highly significant (F = 48.23, p < 0.0001) with R² = 0.9785. The optimal conditions, 68.5% ethanol, 58.2 °C, 38.5 min and 1:31 ratio, gave a predicted yield of 3.67 mg/g DW, which was experimentally validated at 3.66 ± 0.05 mg/g DW (0.27% error). The extracted compound was characterized by HPLC-DAD (retention time 12.48 min, LOD 0.12 µg/mL, LOQ 0.36 µg/mL), FTIR (diagnostic trans-band at 960 cm⁻¹) and UV-Vis (λmax 216, 306 and 320 nm). Among waste fractions, grape skins contained the highest resveratrol content (4.52 mg/g DW). The extract exhibited concentration-dependent radical-scavenging activity with IC50 values of 124.6 µg/mL (DPPH) and 78.3 µg/mL (ABTS). The optimized UAE protocol offers a sustainable, scalable route for valorizing viticulture waste into a high-value nutraceutical ingredient, supporting circular-bioeconomy principles