Sustainable Valorization of Avocado By-Products: Green Extraction of Phenolics with NaDES and Their Use in Fresh-Cut Fruit Preservation

The fresh-cut avocado processing generates significant amounts of by-products, mainly peel and seed, with the peel representing a valuable source of phenolic compounds. In this context, the growing demand for sustainable technologies encourages the use of green solvents for bioactive compound recovery. In this study, natural deep eutectic solvents (NaDES) were evaluated as environmentally friendly solvents for the extraction of phenolic compounds from Hass avocado peels through ultrasound-assisted extraction and for their potential application in fresh-cut avocado. Phenolics were extracted using acidic water, ethanol, and NaDES based on choline chloride as a fixed hydrogen bond acceptor (HBA) and hydrogen bond donors (HBDs; lactic acid, glycerol, and citric acid) with the ultrasound-assisted system. The stability of the extracts was monitored for eight weeks (four weeks in darkness followed by four weeks under light exposure). Among the tested formulations, the lactic-acid-based NaDES showed the highest extraction efficiency and the best stability of phenolic compounds during storage (≥20 mg GAE g−1 dw during the storage period). The lactic-acid-based extract was then applied to fresh-cut avocado to evaluate its potential for antioxidant enrichment and browning prevention during refrigerated storage. The treatment increased phenolic content and contributed to improved color stability (during seven days of storage). Overall, lactic-acid-based NaDES represent a promising green solvent system for recovering phenolics from avocado peel and for their functional application in fresh-cut avocado within a circular valorization approach.