083: Optimizing Ethanol-Water Cosolvent Systems for Green Supercritical Carbon Dioxide Extraction of Muscadine Grape Pomace Polyphenols

Introduction

Muscadine grapevines (Vitis rotundifolia Michx.) are disease-resistant plants indigenous to the southeastern United States. They yield grapes in a variety of sizes and colors, typically characterized by their thick skins and seeds. The production of juice and wine results in considerable waste and by-products, notably muscadine pomace, which comprises the skins, pulp, and seeds remaining after the pressing process. Approximately 20-25% of the weight of the grapes converts to grape pomace, contributing to over 9 million tons of waste generated globally each year. The underutilized by-product of muscadine grape pomace is a rich source of polyphenols with significant antioxidant properties. Conventional extraction methods, such as acidic acetone and methanol, involve organic solvents that pose environmental and health concerns. This study aimed to optimize a green and sustainable SC-CO₂ extraction process using ethanol-water cosolvents to recover polyphenols, maximizing total phenolic content (TPC), total flavonoid content (TFC), and resveratrol yields.

Methods

A central composite response surface design (a total of 16 runs with the center point duplicated) was implemented to evaluate the effects of pressure (20–40 MPa), temperature (40–60°C), and cosolvent concentration (5–15%) on extraction efficiency of the ethanol-water-modified (50%, v/v) SC-CO2. The optimized conditions were determined for TPC, TFC, and resveratrol yields. Extracts were characterized for appearance and antioxidant activity (ABTS and DPPH assays), and results were compared to conventional (HCl-methanol) extractions.

Results

Optimal SC-CO₂ extraction conditions (20 MPa, 60°C, 15% cosolvent) yielded 2491 mg/100 g TPC, 674 mg/100 g TFC, and 1.07 mg/100 g resveratrol. Cosolvent concentration significantly influenced extraction efficiency, with 15% producing red-brown extracts and 5% yielding suboptimal, yellow-green extracts. Higher temperatures (i.e., 60°C) and lower pressures (20 MPa) enhanced the yields. TPC and TFC levels were comparable to conventional methods, though resveratrol and ABTS antioxidant activity were lower than those from HCl-methanol extraction. Moreover, DPPH activity showed no significant difference between methods.

Significance

This study demonstrated the feasibility of ethanol-water-modified SC-CO₂ extraction as a green, food-grade method for recovering polyphenols from muscadine grape pomace. By replacing petroleum-based solvents with environmentally friendly solvents employing statistical optimization, this research advances sustainable technologies for valorizing agricultural wastes.

Authors: Arda Tuhanioglu, Sumanjot Kaur, Gabriel Laquete De Barros, Safoura Ahmadzadeh, Renee Threlfall, and Ali Ubeyitogullari