Abstract: Objective: To extract and purify polysaccharide fractions from the flower of Hylocereus undatus (Haw.)(H. undatus) Britton & Rose and investigate their physicochemical, spectroscopic, and structural properties. Methods: The crude water-soluble polysaccharide (HUP) was extracted, precipitated, deproteinized and lyophilized from flower of H. undatus. A homogeneous polysaccharide fraction, designated HUP0, was obtained by consecutive DEAE-cellulose and Sephadex G-100 column chromatography. Structural characterization of the polysaccharide fraction was conducted using high performance size exclusion chromatography coupled with multi-angle laser light scattering and refractive index detection (HPSEC-MALLS-RID), Fourier transform infrared (FT-IR) spectroscopy, high performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy. Results: The weight-average molecular mass, intrinsic viscosity, specific rotation and mean diameter of HUP0 were measured to be 33.24 kD, 47.16 mL/g, +69°, and 196.96 nm, respectively. The FT-IR spectra showed that HUP0 was a neutral polysaccharide, which mainly contained β-configuration. Methylation, HPLC and NMR analyses indicated that HUP0 was a (1→4)-β-D-galactan.

Key words: flower of Hylocereus undatus (Haw.) Britton & Rose, polysaccharide, structural characterization, galactan