Separation and purification of glabridin from a deep eutectic solvent extract of Glycyrrhiza glabra residue by macroporous resin and its mechanism

Glabridin has beneficial antioxidant, anti-inflammatory, and tyrosinase inhibitory activities, with many applications in the pharmaceutical and cosmetics industries. After industrial extraction of glycyrrhizic acid, Glycyrrhiza glabra residue contains abundant glabridin. Glabridin was extracted from Glycyrrhiza glabra residue with a deep eutectic solvent (DES), followed by the recovery of the glabridin by organic solvent extraction, and then partial purification with hydrophobic macroporous resin. Ethyl acetate was the best extraction solvent, with an extraction yield of 91.63 %. Twelve macroporous resins were evaluated and LSA-21 yielded the best recovery of glabridin. Adsorption of glabridin by LSA-21 resin conformed to pseudo-second-order kinetic and Langmuir models. The thermodynamic parameters ΔH (enthalpy change) and ΔG (Gibbs free energy) were both negative, ΔS (entropy change) was positive. These results indicated that LSA-21 resin spontaneously and exothermically adsorbs glabridin to form a monolayer. The optimum conditions for separating and purifying glabridin by LSA-21 resin were 50 % ethanol aqueous solution(v/v) with a concentration of 56.90 µg/mL glabridin at a flow rate of 2 bed-volumes (BV)/h, and elution with 4 BV of ethanol at 2 BV/h, producing a glabridin yield of 97.80 %. The resin could be reused four times and the glabridin yield slightly decreased to 94 %. The overall recovery of glabridin from the DES Glycyrrhiza glabra extract solution after the ethyl acetate and LSA-21 steps was 89.61 %, with a purity of 17.38 %. This approach is an effective method for the recovery and purification of glabridin from a DES extract of Glycyrrhiza glabra residue, which has potential industrial application for producing glabridin and other natural plant products.