Study on the Extraction of Polyphenols, Polysaccharides, and Saponins from Camellia oleifera Leaves Using Deep Eutectic Solvents and Their Activities

Abstract

Camellia oleifera Abel., a unique Chinese oil crop of the Theaceae family, supplied the leaves from which polyphenols, polysaccharides and saponins were fractionated with deep-eutectic solvents. COSMO-RS and an artificial neural network were coupled to identify the best deep-eutectic solvents for extracting polyphenols, polysaccharides and saponins from C. oleifera leaves. The main findings are as follows: 1. Polyphenols from *Camellia oleifera* leaves were recovered with ultrasound-assisted deep eutectic solvents (DESs); COSMO-RS modelling guided the selection of the most effective DES to maximise yield. After response-surface tuning of sonication time, power and solvent loading, the ultrasonic protocol delivered 131.63 ± 0.85 mg GAE g⁻¹ of polyphenols—twice the haul achieved with classic ethanol soaking. 2. A 9-6-1 ANN, fed with COSMO-RS descriptors, predicted pH and solubility for 36 DES candidates; the choline chloride–sorbitol mixture (ChCl-Sor, pH ≈ 4.5) matched the optimum for protease and cellulase and was chosen for polysaccharide extraction. RSM optimised DES-assisted enzymatic extraction (DES-dEAE): at 33:1 liquid-solid ratio, 3:1 enzyme ratio, 15 min and 40 % water, polysaccharide yield peaked at 21.71 ± 0.21 %. 3. Saponins from *Camellia oleifera* leaves were recovered with ultrasound-assisted deep eutectic solvents (DESs); COSMO-RS modelling guided the selection of the most effective DES to maximise yield. Solid-phase extraction was used to separate saponins from DESs. Preliminary identification showed that saponins from Camellia oleifera leaves include unique saponins such as Oleiferasaponin A3, Sanchakasaponin C, and Sanchakasaponin D. Based on the identification results, COSMO-RS was used to predict the solubility of 36 DESs with six specific saponins. Combined with saponin extraction yield, the DES composed of choline chloride and fructose (ChCl-Fru) was selected as the most suitable DES, with a purified maximum extraction yield of 110.55 ± 0.33 mg TS/g. Experiments demonstrated that the ChCl-Fru group exhibited good antibacterial activity, with significant inhibition against Escherichia coli. The inhibition zone diameter reached 32.87 ± 0.48 mm, superior to the penicillin group, and the growth of E. coli was inhibited at saponin concentrations of 0.78–1.56 mg/mL.