Synthesis and physicochemical properties of polysaccharides by Gluconobacter oxydans with glycosyltransferase activity

Dextran, a homologous polysaccharide with the main chain of glucose units composed by an α-1,6 glycosidic bond, is synthesized from dextrin by dextran-dextrinase (DDase), a transglucosidase, derived from acetic acid bacteria Gluconobacter oxydans and lactic acid bacteria (LAB). The effective culture conditions were examined for producing dextran via bio-conversion with acetic acid bacteria (AAB) demonstrating DDase activity in various medium compositions during 0 to 7 days with or without glycerol addition (2%, v/v) and different degrees of dextrin polymerization (D.E.) based on the addition level (1,5%, w/v). On day 7, the G. oxydans growth was almost tripled in presence of glycerol as observed via a cell growth curve (OD). After culturing for 7 days, the pH decreased from 6 to 3.1-3.5, and the acidity increased from 0.12% to 0.4-0.62%, depending on the dextrin D.E. and the addition level. The reducing sugar decreased continuously. The medium containing 5% dextrin showed shear-thinning characteristics. The apparent viscosity of the 5% dextrin DE4-7 culture solution was 5.6 mPa·s, which was similar to that of the 20% dextran aqueous solution. The analysis of constituent saccharides contained in the culture medium (HPAEC-PAD) showed a substance with a high degree of polymerization. H-NMR analysis showed that α-1,6 glycosidic bond existed as the intermolecular bond of this substance. Therefore, efficient production of dextran was possible by culturing in a medium containing 5% dextrin and glycerol during culture of AAB.