Structure characterization and antioxidant activity of a novel polysaccharide isolated from Ginkgo biloba

Abstract

A novel polysaccharide (GBP50S2) with antioxidant activity was isolated from Ginkgo biloba. The structure of GBP50S2 was elucidated on the basis of physico-chemical and instrumental analyses, and its average molecular weight (Mw = 2.30 × 10⁵) was determined by gel permeation chromatography. The backbone of GBP50S2 was composed of (1 → 4)-linked α-d-mannopyranosyl residues which branched at O-3. The three branches consisted of β-l-rhamnopyranosyl residues, (1 → 4)-linked α-d-galactopyranosyl terminated with β-l-rhamnopyranosyl residues, and (1 → 3,4)-linked α-d-mannopyranosyl terminated with β-l-rhamnopyranosyl residues, respectively. In the in vitro antioxidant assay, GBP50S2 was found to possess DPPH radical-scavenging activity and hydroxyl radical-scavenging activity with an IC₅₀ value of 0.412 mg/mL and 0.482 mg/mL, respectively.

Introduction

Ginkgo biloba L., sometimes referred to the living fossils for its ancient evolutionary root, belongs to spermatophyte which is the only living representative of the Ginkgoales. Extract of G. biloba leaves (EGb 761) is among the most widely sold herbal dietary supplements all over the world. EGb 761 has been reported to have neuroprotective, anticancer, cardioprotective, stress alleviating, and memory enhancing effects and potential benefits against tinnitus, geriatric complaints, and psychiatric disorders [1], [2].

There exist several reports focused on extraction, purification and structural elucidation of polysaccharides from G. biloba during the past years [3], [4], [5]. Polysaccharides isolated from G. biloba have several bioactivities such as anti-inflammation [6] and anticancer effects [7]. However, up until now no investigation has been carried out on polysaccharides of G. biloba that could account for antioxidant activities. Identification of the polysaccharide is necessary to more effectively exploit the structural and functional properties of these substances. In this study, we report on the extraction, purification and structural identification of a novel polysaccharide from G. biloba leaves by using DEAE–cellulose column and DEAE–sepharose fast flow column chromatography. In addition, the structure characterization and antioxidant activity in vitro were also established and assayed.