Structural Characterization and Antioxidant Activity of Polysaccharides and Oligosaccharides from Angelica Keiskei

OBJECTIVE  To extract the polysaccharides and oligosaccharides from Angelica keiskei by using the water extraction and alcohol precipitation methods, and to investigate their physicochemical properties, structure characterization and antioxidant activity.

METHODS  The polysaccharides and oligosaccharides were prepared by the sequential extraction method of cold and hot extraction technique respectively, and fractioned following with membrane dialysis. Chemical analyses were used to determine the contents of total sugar, protein, uronic acid and amino sugar. The molecular weight distribution and monosaccharide composition was determined by high performance gel permeation chromatography(HPGPC) and PMP-HPLC, and the structure were preliminarily characterized by infrared spectroscopy. The antioxidant activity was determined by free radical scavenging activity1,1-diphenyl-2-picrylhydrazyl(DPPH) and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate)(ABTS).

RESULTS  The 4 fractions was found to be quite different by cold maceration and reflux extraction. The molecular weights of the fractions were mainly concentrated in the range of 4–8 kDa(polysaccharides) and 1.5–2.0 kDa(oligosaccharides). Cold-dipped fractionscold-extracted polysaccharide of Angelica keiskei(AKCP) and cold-extracted oligosaccharide of Angelica keiskei(AKCO) were mainly composed by Gal and Ara, while the composition of hot-extracted fractionshot-extracted polysaccharide of Angelica keiskei(AKHP) and hot-extracted oligosaccharide of Angelica keiskei(AKHO) were significantly different. AKHP predominantly constituted of Gal, GalA, Xyl and Ara, with the typical pectin polysaccharide structure. AKHO were mainly composed of Glc, Gal and Rha. All of the 4 fractions showed good antioxidant activity, among which AKCO showed the highest DPPH(IC₅₀ 0.11 mg·mL⁻¹) radical scavenging activity.

CONCLUSION  The molecular weight distribution and monosaccharide compositions of 4 components from Angelica keiskei extracted by the sequential extraction method of cold and hot extraction technique are significantly different. And the 4 components possess obvious antioxidant activity, with potential applications in natural antioxidants.