Tailoring sodium acetate-based NADES for selective recovery of phenolics from red plum peel: impact of composition, preparation method, and multivariate analysis

The present study systematically investigated sodium acetate-based natural deep eutectic solvents (NADES) formulated with different hydrogen bond donors (urea, citric acid, glycerol, and glycine) and prepared using water bath (WB), ultrasound (US), and microwave (MW) methods, with a specific focus on elucidating the role of solvent composition and preparation strategy in extraction efficiency. These solvents were applied for the recovery of phenolics, flavonoids, monomeric anthocyanins, and proanthocyanidins from red plum (Prunus domestica L.) peels, while antioxidant capacity was determined using DPPH radical scavenging, ferric reducing antioxidant power (FRAP), and cupric reducing antioxidant capacity (CUPRAC) assays. Urea-based NADES prepared by MW (N3) exhibited the highest TPC (48.46 g GAE/kg dm), DPPH activity (179.03 g TEAA/kg dm), and FRAP values (189.67 g TEAA/kg dm). The highest TFC was obtained using urea-based NADES prepared by US (N2), reaching 3884.98 mg CE/kg dm. Regarding pigment recovery, glycerol-based NADES prepared by US (N8) achieved the highest TMAC (7103.19 mg C3G/kg dm) and TPAC (34.04 mg cyanidin/kg dm), followed by glycine-based NADES prepared by WB (N10) (7093.63 mg C3G/kg dm; 29.43 mg cyanidin/kg dm). Overall, urea-based systems were more effective for phenolics and antioxidant activity, whereas glycerol- and glycine-based NADES were superior for anthocyanin and tannin extraction. These findings demonstrate, for the first time, that tailoring both NADES composition and preparation methodology enables targeted compound recovery, highlighting the strong potential of sodium acetate-based NADES as sustainable solvents for fruit by-product valorisation. Sodium acetate-based NADES enabled efficient recovery of plum peel phenolics. Preparation method (MW, US, WB) significantly influenced extraction efficiency. Urea-based NADES showed superior performance for TPC, TFC, and antioxidant assays. Glycine-based systems yielded the lowest recoveries, confirming limited suitability. PCA revealed distinct clustering of antioxidant activity and phenolic composition. Red plum peel valorisation supports sustainable use of fruit-processing by-products.