Efficient extraction of proanthocyanidin from Ginkgo biloba leaves employing rationally designed deep eutectic solvent-water mixture and evaluation of the antioxidant activity

Proanthocyanidin (PAC) holds strong free radicals scavenging ability and is widely used as oxygen free radical scavenger. Huge demand, safety and economic aspect are forcing the PAC extraction to explore new resource and greener solvent. An efficient extraction method of PAC from Ginkgo biloba leaves was established by employing deep eutectic solvent (DES)-water mixture. After a rational design, a DES-water mixture (named as Ch-M55) was chosen as the extraction solvent, which was prepared from choline chloride and malonic acid at a molar ratio of 1:2 with water addition of 55% (w/w). The main factors affecting the extraction yield were statistically optimized using a central composite design combined with response surface methodology (RSM). The optimal conditions were obtained as follows: extraction temperature of 65 °C, extraction time of 53 min and Ch-M55 to solid ratio of 10.57:1 (v/w, mL/g). The PAC extraction yield was 22.19 ± 0.71 mg/g under the optimized conditions, which was much higher than those of conventional organic solvents. The antioxidant activity of PAC extracted by Ch-M55 was similar to that of 70% acetone, but a little less than 70% methanol and 70% ethanol. The differences in constituent and polymerization degree of PAC extracted by different solvents might account for the difference in antioxidant activity. In consideration of biodegradability and pharmaceutical acceptability, the Ch-M55-based extraction method is obviously efficient, green and ecofriendly. Extraction of PAC from Ginkgo biloba leaves also provides a new PAC resource.