Advancements in Green Extraction of Polyphenols from Fetească albă Grape Pomace Using Natural Deep Eutectic Solvents: Optimization and Applications as Inhibitors for Enzymatic Browning

What if the leftover grape skins from winemaking could hold the key to keeping your sliced apples fresh and un-browned? This study turns that pomace into a powerful, green enzyme inhibitor.

In the quest for sustainable solutions, researchers have turned to an unlikely hero: white grape pomace from the Fetească albă variety. This winemaking byproduct, often discarded, is packed with polyphenols that can inhibit the enzymes responsible for enzymatic browning in fruits. The team used a natural deep eutectic solvent (NaDES) made from choline chloride and lactic acid, with a splash of water, to extract these valuable compounds via ultrasound-assisted extraction. After optimizing the process with response surface methodology, they achieved impressive yields at 60°C for 30 minutes with a liquid-to-solid ratio of 10 mL/g. The extract boasted a total polyphenolic content of 68.89 mg gallic acid equivalents per gram of dry weight, along with flavonoids and strong free-radical scavenging activity. Phenolic acids dominated the profile, making up 70% of the polyphenols, with vanillic acid as the star compound. When tested against apple polyphenol oxidase (PPO) and peroxidase (POX), the extract showed potent inhibition, with IC50 values of 0.30 mg GAE/mL for PPO and 33.24 µg/mL for POX. Molecular docking revealed that the major phytochemicals bind to PPO away from the active site, suggesting a non-competitive mechanism, while they directly interact with POX's active site, hinting at a competitive inhibition. This green extraction method not only valorizes waste but also offers a natural alternative to synthetic anti-browning agents.

Key Points

• Green NaDES extraction from grape pomace yields high polyphenols.
• Extract inhibits apple browning enzymes PPO and POX.
• Molecular docking reveals different inhibition mechanisms for PPO vs POX.