Structure identification of a polysaccharide purified from Lycium barbarium fruit

The water-soluble bioactive polysaccharides can contribute to the health benefits of Lycium barbarium fruit. However, the structure characteristics of these polysaccharides remain unclear yet. An important polysaccharide (LBPA) was isolated and purified from L. barbarium in this work. It was identified by chemical and spectroscopic methods as arabinogalactan with β-d-(1 → 6)-galactan as backbone, which was different to any reported polysaccharides from this species before. This arabinogalactan was comprised of Araf, Galp, GlcpA and Rhap with a molar ratio of 9.2:6.6:1.0:0.9. The side chains, including α-l-Araf-(1→, α-l-Araf-(1 → 5)-α-l-Araf-(1→, β-l-Araf-(1 → 5)-α-l-Araf-(1→ and α-l-Rhap-(1 → 4)-β-d-GlcpA-(1 → 6)-β-d-Galp-(1→, were linked to β-d-(1 → 6)-galactan at O-3. The putative structure was drawn as below. The molecular weight was determined to be 470,000 g/mol by gel permeation chromatography.