Structural elucidation and antioxidant activity of an arabinogalactan from the leaves of Moringa oleifera

A novel arabinogalactan (MOP-1) was isolated from leaves of Moringa oleifera and was purified by macro-porous resin, DEAE-52 Cellulose and Sepharose 6B gel filtration chromatography. High performance gel permeation chromatography (HPGPC) analysis showed that the molecular weight of MOP-1 was 7.65 × 107 Da. Monosaccharide composition analysis indicated that sugar composition is Rha: Ara: Gal in a molar ratio of 1:7.32:12.12. Structural analysis indicated that MOP-1 has a backbone of →1)-β-d-Galp-(3,4→ with highly branched chains at O-4 position. The branches were composed of →1)-β-d-Galp-(4→, →1)-α-d-Galp-(2→, Araf-(1→, Galp-(1→. Its antioxidant activities were evaluated by DPPH radical scavenging capacity, 2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical cation scavenging capacity, and ferric-reducing antioxidant power (FRAP). The results indicated MOP-1 exhibited significant antioxidant activities.