Structural characteristics, antioxidant properties and antiaging activities of galactan produced by Mentha haplocalyx Briq.

An antioxidant-active polysaccharide (WMP) with a molecular weight of 26.91 kDa was isolated from Mentha haplocalyx Briq by water extraction, ethanol precipitation and gel filtration. According to HPLC, methylation, GC-MS, and 1D/2D nuclear magnetic resonance spectroscopy, WMP is a heteropolysaccharide composed of Gal (84.2 %), Glc (9.8 %), Man (2.8 %) and Ara (3.2 %) with (1→6)-α-d-Galp and (1→4, 6)-α-d-Galp residues in the backbone and (1→6)-α-d-Galp and (1→6)-α-d-Glcp residues in the branch. The branch point was located at C-4 of (1→4, 6)-α-d-Galp residue with a branching degree of 19.71 %. WMP showed remarkably high scavenging ability for 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals, ferrous ion chelating activity and ferric reducing powder in vitro. In vivo result showed that WMP oral administration substantially increased the activities of antioxidant enzymes, including SOD, GSH-Px and CAT, and decreased MDA levels in the serum and liver of d-Gal-induced aging mice. Therefore, WMP can be an effective natural antioxidant.