Green extraction of phenolic compounds from Hippophae gyantsensis leaves using natural deep eutectic solvents: Antioxidant and antimicrobial activities

This study employed a choline chloride-acetic acid-based natural deep eutectic solvent (NADES-1) combined with ultrasound-assisted extraction to recover polyphenols and flavonoids from Hippophae gyantsensis leaves. The statistically validated optimal conditions included 32 % water content, 24:1 ( v / w ) liquid–solid ratio, and 53 °C extraction temperature. This three-parameter synergistic optimization approach maximized the yield of the target active compounds. Under these conditions, the yields reached 108.36 ± 0.11 mg gallic acid/g for total phenolics (TP) and 67.12 ± 0.53 mg rutin/g for total flavonoids (TF), with an antioxidant capacity of 82.5 ± 1.45 mg vitamin C equivalents/g, significantly outperforming conventional 60 % ethanol extraction. The purified NADES-1 extract demonstrated remarkable antioxidant activity: 2,2-Diphenyl-1-picrylhydrazyl (DPPH) IC 50  = 57.63 ± 1.38 μg/mL, Lipid Peroxidation (LPO) IC 50  = 53.57 ± 0.32 μg/mL, and antimicrobial effects: Minimum Inhibitory Concentration (MIC) against Escherichia coli  = 0.63 mg/mL), surpassing those of ethanol-purified extracts. Pearson correlation analysis revealed strong positive associations between TP / TF contents and bioactivities, suggesting these compounds may serve as key contributors to the observed effects.