Enhanced Extraction of Bioactive Compounds from Red Grape Pomace: Optimizing Ultrasound-Assisted Extraction with Ethanol and NaDES as Solvents

What if the secret to unlocking grape pomace's hidden treasure lies in a solvent that's both eco-friendly and surprisingly effective? A new study pits ethanol against a natural deep eutectic solvent (NaDES) in an ultrasound-assisted battle for polyphenols.

Red grape pomace, a winemaking byproduct, is packed with bioactive compounds—but extracting them efficiently is a challenge. Researchers tested two solvents: ethanol, the classic choice, and a natural deep eutectic solvent (NaDES) made from choline chloride, lactic acid, and water in a 1:2:1 molar ratio. Using ultrasound-assisted extraction, they optimized conditions with response surface methodology to maximize yields of anthocyanins, polyphenols, flavonoids, and antioxidant activity.

For ethanol, the sweet spot was 70% concentration at 35°C for 22.5 minutes, yielding impressive values—105.32 mg C3G/g DW for anthocyanins and 465.81 mg GAE/100 g DW for polyphenols. NaDES required warmer conditions (60°C, 60 minutes) and produced slightly lower polyphenol content but comparable flavonoid levels. However, ethanol extracted more diverse compounds: 12 polyphenolic compounds identified versus just 5 with NaDES.

An in vitro digestion study revealed that polyphenols are highly bioaccessible in the gastric environment but drop drastically in intestinal fluid. This suggests that while NaDES offers a greener alternative, ethanol remains superior for broader compound recovery—yet both solvents provide valuable, non-toxic options for industry.

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