Structural characterization of water-soluble polysaccharides from Opuntia monacantha cladodes in relation to their anti-glycated activities

An aqueous extract of polysaccharides from Opuntia monacantha cladodes (PONIQ was preliminarily purified by 5 kDa molecular weight cut-off ultrafiltration membrane to remove impurities with low molecular weight. Then the retentate was fractionated by ethanol solution and chromatographed on a DEAE Sepharose Fast Flow anion-exchange column to yield a major fraction (PONIC IV) which was eluted by 0.5 M NaCl. PONIC IV was subjected to further purification on a Sephadex G-50 gel filtration column. Two major fractions, POMC V and V1, were collected. By analyses using gel permeation chromatography (GPQ, high-performance liquid chromatography (HPLQ and gas chromatography (GQ, POMC V, which had a molecular weight of 28.7 kDa, was comprised mainly of rhamnose, arabinose and glucose in the molar ratio of 9.15:1.00:6.84, with 3.07% (w/w) of glucuronic acid, while POMC VI, which had a molecular weight of 10.8 kDa, was comprised mainly of rhamnose, mannose and glucose in the molar ratio of 8.72:1.00:6.19, with 4.68% (w/w) of glucuronic acid. Six distinct-absorbance peaks, at 1742, 163 3 and 1417 cm(- 1) in the infrared (IR) spectra of PONIC V, and at 1729, 1596 and 1407 cm- 1 in the IR spectra of PONIC VI, resulted from the presence of uronic acids. The peaks at 1043 and 890 cm- 1 were characteristic of rhamonse and beta-D-glUCOse, respectively. From the profiles of 13 C and H-1 nuclear magnetic-resonance (NMR) spectra, the main (1 -> 2)-alpha-L-rhamnopyranose units were obviously characterized by six strong signals at 99.24 (C-1), 77.52 (C-2), 70.19 (C-3), 71.33 (C-4), 69.81 (C-5) and 17.45 ppm (C-6). The signal at 175.92 ppm was due to C-6 Of P-D-glucuronic acid units. The 1 H spectrum signal at 1.20 ppin was assigned to the CH3 Of alpha-L-rhamnopyranose units. The evaluation of anti-glycation activity suggested that PONIC had good potential for inhibiting the formation of advanced glycation endproducts. Time- and dose-dependent effects were also observed for all PONIC samples. (c) 2007 Elsevier Ltd. All rights reserved.