Application of an eco-friendly sodium acetate/urea deep eutectic solvent in the valorization of melon by-products

Abstract An eco-friendly sodium acetate/urea (NaOAc:urea:water) deep eutectic solvent (DES) was evaluated for the extraction of bioactive compounds from melon peels. Melon peels were first extracted with water to separate the water-insoluble solids (WIS) from free sugars, and the WIS were subsequently extracted with the DES. The extracts were analyzed for oligosaccharides and protein as well as total phenolic content and antioxidant activities. The influence of extraction parameters (time, temperature, DES molar ratio, water content and solid consistency) on the composition of the extracts was evaluated. At the selected conditions (NaOAc:urea:water with molar ratio 1:3:1.6 (10% (w/w) water), with a consistency of 2% (w/w), at 90 °C for 10 min), the total oligosaccharide yield was 8.84 g oligosaccharides/100 g WIS, of which 90% were oligogalacturonides, and the total phenolic content and protein content were 4.35 mg GAE/g WIS and 2.87 g/100 g WIS, respectively. Pectin enriched in branched rhamnose units with a low degree of methyl esterification was recovered by precipitation, with a yield of 7.95 g/100 g WIS and a galacturonic acid content of 49.44%.