Chemical characterisation and gelling properties of cell wall polysaccharides from species of Ulva (Ulvales, Chlorophyta)

Two alkali-soluble polysaccharide fractions from the cell wall of Ulva ‘rigida’ were determined to be β-1,4-linked glucoxylans and a β–1,4-linked glucuronan by chemical and NMR spectroscopic analysis. The 13C NMR spectrum of water-soluble xyloglucuronorhamnan sulfate from Ulva ‘rigida’ referred to as ulvan is reported and the 13C and 1H NMR chemical shifts of its major repeating unit, the aldobiuronic acid β-D-GlcA-(1,4)-L-Rha, are given. The composition and gelling properties of ulvan from Ulva species from ‘green tides’ are also reported. The thermoreversible gel required both calcium and borate ions and the shear storage modulus G’ was ion concentration dependent. The mechanism of gelation and the associations of the different Ulva cell wall soluble polysaccharides are discussed.