Isolation, characterization, and antioxidant activity of neutral carbohydrates from Astragalus arbusculinus gum

Abstract

“Anzaroot” is an exudate gum obtained from Astragalus species in Iran. Plant gum exudates contain hydrophilic biopolymers, and carbohydrates are the most important ingredients in the gums. Carbohydrates possess different biological properties like enhancement of immunity and antioxidant effect. This study aimed to isolate the novel carbohydrates from Astragalus arbusculinus Bornm. & Gauba gum and investigate their monosaccharides composition and antioxidant activity. For this purpose, the crude water-soluble A. arbusculinus extract was fractionated by DEAE-52 column chromatography. The A. arbusculinus carbohydrate (AAC) fraction was analyzed by high-performance liquid chromatography- evaporative light scattering detector (HPLC-ELSD), and eight compounds, including two major, were detected in its chromatogram. Subsequently, preparative-thin layer chromatography (prep-TLC) was used to isolate and purify the two major compounds, named AAC1 and AAC2. The structural features of AAC1 and AAC2 were investigated by a combination of monosaccharide component analysis using fourier-transform infrared spectroscopy (FT-IR), gas chromatography–mass spectrometry (GC–MS), gas chromatography with a flame ionization detector (GC-FID), and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). The results indicated that AAC1 was composed of six monosaccharide components, including glucose, rhamnose, and arabinose, with a relative molar ratio of 4:1:1 and molecular weight 971.4531 Da approved by GC–MS and MALDI-TOF analyses, respectively. Also, AAC2 was composed of six monosaccharide units, including glucose, pinitol, and arabinose, with a relative molar ratio of 4:1:1 and molecular weight of 987.4084 Da. Radical scavenging activity of the two compounds was also evaluated against DPPH.