Isolation, structural characterization, and antioxidativity of polysaccharide LBLP5-A from Lycium barbarum leaves

A water-soluble polysaccharide, LBLP5-A, was isolated from Lycium barbarum leaves, which is widely used as a medicine in Asia. The average molecular weight of LBLP5-A is 11.33 x 10(4) Da. With O-type carbohydrate-peptide linkage in its structure, LBLP5-A afforded glycan fractions of LBLP5-A-OL1, LBLP5-A-OL2, LBLP5-A-OL3, and LBLP5-A-OL4 acquired by beta-elimination reaction. Detailed structure patterns of LBLP5-A-OL1 were characterized by monosaccharide composition analysis, methylation analysis, partial acid hydrolysis, Smith degradation, one- or two-dimensional (1D/2D) nuclear magnetic resonance (NMR), and electrospray ionization-mass spectrometry (ESI-MS). LBLP5-A-OL1 was identified to be a highly branched polysaccharide with a backbone of (1 -> 3)-linked Gal, which was partially substituted at its O-6 position. These branches, with arabinose and galactose terminals, were assigned to be (1 -> 3)-linked Gal, (1 -> 4)-linked Gal, (1 -> 3)-linked Araf, (1 -> 5)-linked Araf, and (1 -> 2, 4)-linked Rhaf. LBLP5-A-OL3 and LBLP5-A-OL4 were determined to be a series of oligosaccharides that share the general structure pattern of Ara(n1)-> Gal(n2)-> Rha(n3) (n1=0-6, n2=0-8, n3=0-1) by ESI-MS. Moreover, LBLP5-A exhibited excellent antioxidativity, concerning the scavenging abilities on 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide, and hydroxyl radicals in vitro. (C) 2015 Elsevier Ltd. All rights reserved.