Efficient Separation of Proteins and Polysaccharides from Dendrobium huoshanense Using Aqueous Two-Phase System with Ionic Liquids

By applying the hydrophilic ionic liquid, 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), and inorganic salts (K3PO4), an ionic liquid aqueous two-phase system (ILATPS) was established for the separation of Dendrobium huoshanense polysaccharides (DhPs) and proteins. The effects of inorganic salt concentration, IL quantity, crude DhPs concentration, pH value and temperature were studied to achieve the optimal condition. With the best combination of ILATPS (1.75 g K3PO4, 1.25 g [C4mim]Cl, 10 mg crude DhPs and 5.0 mL ddH2O at pH 7.0 under 25 °C), the extraction efficiency rates for DhPs and proteins were 93.4% and 90.2%, respectively. The processed DhPs retrieved from the lower salt-rich phase comprised mannose, glucose, galactose, arabinose, and galacturonic acid with a molar ratio of 185:71:1.5:1:1 and the molecular weight was 2.14 × 105 Da. This approach is fast, simple and environmentally friendly. It provides a new insight into purifying functional polysaccharides of plant origin.