The bacteria Leuconostoc mesenteroides (strain NRRL-B512) has been used for the fermentative production of the polysaccharide dextran from sucrose. The polysaccharide production was carried out via a four-step process involving (1) production of the enzyme dextransucrase (DS), (2) bacteria removal from the culture broth, (3) enzyme purification by gel permeation chromatography, and (4) enzymatic synthesis of dextran in a cell-free reaction medium.
The enzymatic reaction was followed measuring the change in rheological properties of the reaction medium with time at different initial substrate concentrations. The influence of other parameters, such as temperature, addition of acceptor molecules (maltose), and enzyme purity, were also considered.
The microbial extracellular polysaccharide is responsible for the non-newtonian character of the reaction media. At low shear rate values the flow behavior was newtonian, whereas at higher shear rates the reaction media exhibited a marked shear-thinning behavior. The Carreau equation appears to fit fairly well the experimental data over several decades of shear rate. The reaction media showed elastic behavior as well.