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Water-insoluble glucans from sucrose via glucansucrases. Factors influencing structures and yields

Gregory L. Cote, Christopher D. Skory
Green Polymer Chemistry: Biobased Materials and Biocatalysis 2015 ch.7 pp. 101-112
Leuconostoc mesenteroides, Streptococcus, amino acids, biobased products, biocatalysis, carbohydrate structure, dextran, enzyme substrates, glucosyltransferases, lactic acid bacteria, oils, physical properties, polymers, sucrose, synthesis
Dextrans and related glucans produced from sucrose by lactic acid bacteria have been studied for many years and are used in numerous commercial applications and products. Most of these glucans are water-soluble, except for a few notable exceptions from cariogenic Streptococcus spp. and a very small number of Leuconostoc mesenteroides strains. The ability to produce water-insoluble glucans in situ may be of value in enhanced oil recovery, encapsulation technology and in the production of biocompatible films and fibers. There are several different ways in which these enzymes can be exploited to produce water-insoluble glucans with varying properties. In previous work, we found that modifying a single amino acid from a L. mesenteroides glucansucrase significantly altered the proportions of linkage types, with correlating changes in the physical properties of the polysaccharide. Here we present results of our studies on factors affecting the structures and yields of these insoluble glucans. For example, addition of soluble dextran or an enzyme that produces a soluble dextran can increase the yield of insoluble glucan. However, the insoluble glucan product contains a lower proportion of α(1→3) linkages. We also show that the yield is drastically affected by both substrate and enzyme concentrations. Studies using cloned enzymes indicate no significant differences between the insoluble-glucan producing enzymes from L. mesenteroides strains NRRL B-523 and B-1118.