Preparation and characterization of dextran from Leuconostoc mesenteroides.

In conjunction with investigations on the a-l, 6-glucosidic linkage in starch, it was desirable to conduct comparative studies on other substances containing this linkage. The dextran from Leuconostoc mesenteroides, a polysaccharide having predominantly a-1 ,6-glucosidic linkages, was selected to be used directly in these comparative studies and to provide a source of simpler substances containing this linkage of rare occurrence. Experiments were designed to provide a dependable source of dextran of high purity and of reproducible high viscosity. Improvements have been made over methods previously described for the preparation of this polysaccharide (l-4), and procedures have been established for the preparation of dextrans of low as well as of high viscosities. Factors Injhencing Dextran Production-Numerous factors, only a few of which have been studied (1,4), appear to influence the properties and the amount of the dextran and of the by-products produced from sucrose by cultures of Leuconostoc mesenteroides. A factor of outstanding importance is the strain of the organism (5), which appears to determine whether the dextran is water-soluble or water-insoluble (3, 6). The structural basis for this difference in solubility is not known. Previously reported dextrans, most of which originated from different strains of Leuconostoc mesenteroides, have varied in other physical properties. Dextran has been obtained in yields of 18 (3) and 25 per cent (4), with specific rotations of +178” to +184” (2, 6,7), of +195” (8), and of +198” (9). It has been reported to have high (2,4,6) and low (1,9) contents of nitrogen, phosphorus, and ash. Some viscosity data for dextran are not on a comparable basis (7, 8) and other data present unexplained variations (5). The optimum pH range for the enzymatic synthesis of dextran has been shown by Hehre to be 4.0 to 6.0 (7, 10). When preparing dextran from cultures of Leuconostoc mesenteroides, neutralization of the acidic byproducts has been reported to increase the yield of dextran (1, 4, 11). The incubation time used previously for the production of dextran has