Isolation, structural characterization, and biological activities of galactomannans from Rhizopogon luteolus and Ganoderma adspersum mushrooms

Abstract

Polysaccharides are essential compounds that contribute to the biological activities of mushrooms. Two new galactomannans (Galactomannan I and II) were isolated from R. luteolus and G. adspersum. Their structures were characterized using FT-IR, 1D, and 2D-NMR techniques. Both isolated galactomannans I and II mainly include D-mannose and D-galactose in the molar percentages of 0.81:1.0 and 1:1.4, respectively. The GPC calculation demonstrated that the molecular weights are about 5240 and 5090 Da, respectively. Their structures comprise of β-(1,4)-mannose (Man) backbone units with α-(1,6)-galactose (Gal) single unit as a side group. The anticholinesterase activity of galactomannans was tested against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), spectrophotometrically. Antioxidant activity was also measured by six assays (ABTS•+, DPPH•, O2•−, β-carotene-linoleic acid, metal chelating, and CUPRAC assays). Galactomannan II indicated close inhibitory activity to galantamine against AChE (61.04 ± 0.45%) and BChE (59.70 ± 1.15%) at 50 μg/mL concentration. Nevertheless, both galactomannans showed low antioxidant activity in all tests. This study reveals that mainly, Galactomannan II could be used as a new natural promising anticholinesterase agent.