Characterisation of polysaccharides synthesised by Gluconobacter oxydans NCIMB 4943

Abstract

Fermentation of Gluconobacter oxydans NCIMB 4943 using malto-oligosaccharides of differing average degrees of polymerisation (DP) as substrates resulted in the synthesis of dextrans consistent with the action of the enzyme dextran–dextrinase (DDase). These dextrans could be precipitated from the fermentation broth using Fehling's solution. The glycosyl linkage composition of the dextrans was largely independent of the size of the initial substrate used and fermentation time. They contained an average of 83mol% 6-linked, 8mol% 4-linked, 6mol% terminal and 3mol% 4,6-linked glucopyranosyl residues. The dextrans gave viscous solutions that displayed shear-thinning behaviour. In addition to the synthesis of dextrans, the fermentations of G. oxydans with malto-oligosaccharides also resulted in the formation of oligosaccharides that were soluble in Fehling's solution. These oligosaccharides contained varying proportions of 4-Glcp and 6-Glcp residues depending on the size of the initial substrate and the culture time. These oligosaccharides may have prebiotic properties.