Structural characterization of LbGp1 from the fruits of Lycium barbarum L.

A water-soluble polysaccharide with a protein content of 3.75%, designated as LbGp1, was isolated from the fruit of Lycium barbarum L. The average molecular weight of LbGp1 was 49.1 KDa determined by high performance gel permeation chromatography (HPGPC). Sugar composition analysis revealed that it was composed of Ara and Gal in a molar ratio of 5.6:1. The existence of O-glycopeptide bond in LbGp1 was demonstrated by β-elimination reaction. Structure of LbGp1 was characterized based on monosaccharide composition, partial hydrolysis, methylation analysis and electrospray ionization mass spectrometer (ESI-MS). LbGp1 was identified to be a highly branched polysaccharide with a backbone of →6)Galp(1 → linked galactose substituted at O-3 by galactosyl or arabinosyl groups. The branches were composed of (1 → 3)-linked-Galp, (1 → 4)-linked-Galp, (1 → 2)-linked-Araf and (1 → 3)-linked-Araf, and arabinose was located at the terminal of the branches.