Utilization of pomegranate peel waste: Natural deep eutectic solvents as a green strategy to recover valuable phenolic compounds

Pomegranate peel is an agro-industrial waste rich in phenolic compounds that can be employed like natural antioxidants in the food and pharmaceutical industry. In this study, five choline chloride-based natural deep eutectic solvents (NADES), which contained glucose, sucrose, glycerol, lactic acid, and citric acid as a hydrogen bond donor, were physicochemically characterized and tested for recovery of phenolics from pomegranate peel. The efficiency of the NADES in extracting phenolics from pomegranate peel has also been compared with that of conventional ethanolic extraction. The choline chloride and lactic acid (CC-LAC) NADES proved to be the most appropriate for the extraction of phenolics from pomegranate peel (4.14 mg EAG mL−1) if compared to the other tested NADES (range 0.81–3.84 mg EAG mL−1) and also if compared with the ethanolic solution (3.55 mg EAG mL−1). The optimization of the extraction conditions of phenolics from pomegranate waste peels using CC-LAC was carried out by multivariate strategies such as factorial design and response surface methodology. The optimal extraction conditions were 20 g of CC-LAC per g of pomegranate peel, 35% of lactic acid in relation to choline chloride, and 25 min of extraction at 45 °C. Under optimal extraction conditions, the phenolic recovery increased by 54.6%, when compared to CC-LAC non-optimized, and by 84.2%, when compared to ethanolic extraction. Our results, therefore, demonstrated that the use of NADES is a simple, cost-effective, more sustainable, and greener alternative for the extraction of the phenolics from pomegranate peel, over conventional extraction methods.