Abstract:
Treatment of aqueous extracts of the fruit of C. abyssinica, containing 0.25% sodium chloride with
three volumes of ethanol produced an acidic polysaccharide with a 2% yield, on a fresh weight basis.
With a protein content between 2.6% and 4.6%, the polymer contained 0.29% hydroxyproline. Uronic
acid content, determined using the m-hydroxydiphenyl method was 9%. Some uronic acid residues
along the polymer chain were methyl esterified, with the methoxyl content being 38%. With an ash
content of 17% the polymer had a mineral ion content of Ca, 0.3%, Mg, 0.3%, Na, 0.2% and K, 4.8%.
The optical rotation of a 0.25% solution was – 50 o. The molecular weight of the polysaccharide
crudely estimated by viscometry was approximately 1 800 000 daltons. Acid and enzymatic
hydrolysis, followed by HPLC and TLC analysis, revealed that the polysaccharide consisted of
glucose, galactose, mannose, arabinose, xylose, rhamnose, fucose, galacturonic acid and an
unidentified sugar. Solutions of the polysaccharide showed pseudoplastic flow behaviour. When
suspended in water, the polysaccharide that was precipitated with salt and ethanol formed gels at a
concentration of 2% at room temperature and at 4 oC. Emulsions formed by the polysaccharide at
neutral and alkaline pH were less stable than those formed by gum arabic. Emulsion formation was
enhanced by increasing the concentration of polysaccharide and the emulsions formed remained stable
even under conditions of high salt concentration. On its own, the polymer formed brittle films but
flexible films were formed in the presence of 1% glycerol. Apples coated with films based on the
polysaccharide lost 33% less moisture than uncoated apples after 30 days of storage at room
temperature. Composite films, prepared in the presence of up to 1.5% starch, had improved elastic
properties.
