Structural characterisation of polysaccharides purified from longan (Dimocarpus longan Lour.) fruit pericarp

In this work, crude polysaccharides were extracted from longan fruit pericarp by hot water. After removal of proteins and purification by Sephadex G-100 gel filtration column, polysaccharides of longan fruit pericarp (PLFP) were subjected to structural identification. Gas chromatography analysis indicated PLFP comprised of l-arabinofuranose (32.8%), d-glucopyranose (17.6%), d-galactopyranose (33.7%) and d-galacturonic acid (15.9%). The glycosidic linkages were determined by methylation analysis and gas chromatography/mass spectrometry (GC/MS). The results showed that the backbone consisted of →5)-l-Araf-(1→, →6)-d-Glcp-(1→, →3)-d-Galp-(1→, →3)-d-GalpA-(1→ and →6)-d-Galp-(1→ with a molar proportion of 2:1:1:1:1. The infrared spectra and nuclear magnetic resonance (NMR) spectra further confirmed that the configuration of l-arabinofuranose was of α-form, while d-glucopyranose, d-galactopyranose and d-galacturonic acid were of β-form. The molecular weight of PLFP was measured to be 420 kDa by gel permeation chromatography. By determination of the anti-glycated activity, PLFP showed a good potential in inhibiting the glycation reaction in vitro.