Patent GB-716660-A (GB)
Title: Production and fractionation of dextrans
IPC: C08B37/02
Filed: 1952-05-12
Abstract: Addition products are obtained by adding alkaline earth hydroxides to solutions of dextran, and these may be decomposed by acids to give free dextran in solution and insoluble alkaline earth metal salts. The process is particularly applicable to the purification of dextran from fermentation residues containing it and to the fractionation of dextran and/or partially degraded dextrans of different molecular weight.  The latter may be achieved either by fractional addition of alkaline earth hydroxide, the lower molecular weight complexes being precipitated first, or by fractional acidification of the precipitate when the higher molecular weight complexes are preferentially dissolved.  The inorganic salts can be removed from the dextran solution by dialysis or adsorption on ion-exchange resins.  When calcium hydroxide is added to fermentation residues containing dextran and fructose the precipitated complex contains both these but with strontium and barium only the dextran is precipitated.  If the fructose is not wanted it can be destroyed with yeast before the precipitation.  The hydroxide may be formed in situ by mixing solutions of an alkaline earth salt and an alkali hydroxide.  The decomposition of the complex may be effected with sulphuric acid, phosphoric acid, oxalic acid, sulphur dioxide or carbon dioxide.  In the examples (1) the residue from the growth of Leuconostoc mesenteroides in a medium containing sucrose is treated with calcium chloride and sodium hydroxide solutions when a mixed dextran-fructose complex is precipitated; this can be decomposed with carbon dioxide; (2) as in (1) the fructose being first decomposed with S. cerevisiae; (3) as in (2) using barium hydroxide, the precipitate being decomposed with sulphuric acid; (4) as in (1) the resulting solution being treated with ethanol to precipitate the dextran which is filtered off and dried, fructose is then crystallized from the solution; (5) raw dextran from the growth of L. mesenteroides on sucrose is partially degraded with hydrochloric acid and the solution treated with caustic soda and calcium chloride; the separated precipitate is treated with successive amounts of sulphuric acid, the solution being removed after each addition, de-ionized with a resin and dried in vacuo.  Six fractions of partially-degraded dextran are thereby obtained; (6) as in (4) the complex being fractionally precipitated instead of fractionally decomposed; (7) the dextran used for process (5) or (6) isobtained by method (2).ALSO:Dextran is purified by precipitating a complex with an alkaline earth metal hydroxide and decomposing it with an acid to give free dextran in solution and an insoluble alkaline earth salt.  The process is particularly applicable to the fractionation of dextran and/or partially degraded dextrans of different molecular weight such as the product of Specification 583,378, [Group IV].  Thus the alkaline earth metal hydroxide may be added in stages, the lower molecular weight complexes being precipitated first, or the whole may be precipitated and fractionally decomposed with acid, the higher molecular weight complexes being preferentially dissolved.  The inorganic salts can be removed from the dextran solution by dialysis or adsorption on ion-ex-change resins.  When calcium hydroxide is added to fermentation residues containing dextran and fructose the precipitated complex contains both these but with strontium and barium only the dextran is precipitated. If the fructose is not wanted it can be destroyed with yeast before the precipitation.  The hydroxide may be formed in situ by mixing solutions of an alkaline earth salt and an alkali hydroxide.  The decomposition of the complex may be effected with sulphuric acid, phosphoric acid, oxalic acid, sulphur dioxide or carbon dioxide.  In the examples, (1) the residue from the growth of Leuconostoc mensenteroides (in a medium obtained by adding sucrose to a yeast culture) is treated with calcium chloride and sodium hydroxide solutions when a mixed dextran-fructose complex is precipitated; this is decomposed with carbon dioxide; (2) as in (1) the fructose being first decomposed with S. cerevisiae; (3) as in (2) using barium hydroxide, the precipitate being decomposed with sulphuric acid; (4) as in (1) the resulting solution being treated with ethanol to precipitate the dextran which is filtered off and dried; (5) raw dextran from the growth of L. mesenteroides on sucrose is partially degraded with hydrochloric acid and the solution treated with caustic soda and calcium chloride; the separated precipitate is treated with successive amounts of sulphuric acid, the solution being removed after each addition, de-ionized with a resin and dried in vacuo.  Six fractions of partially-degraded dextran are thereby obtained; (6) as in (4) the complex being fractionally precipitated instead of fractionally decomposed; (7) the dextran used for process (5) or (6) is obtained by method (2).ALSO:A culture medium for the production of dextran by Leconostoc mesenteroides is obtained as follows: a medium is prepared from sugar, potassium phosphate, magnesium sulphate, sodium chloride and ammonium sulphate, adjusted to pH 4.8 with sulphuric acid.  An active yeast culture of S. cerevisiae is then added and air blown through until the medium is free of sugar.  Finally sucrose is added and the pH brought to 7.0 with sodium hydroxide.