SEPARATION AND QUANTITATIVE-DETERMINATION OF NANOGRAM QUANTITIES OF MALTODEXTRINS AND ISOMALTODEXTRINS BY THIN-LAYER CHROMATOGRAPHY

Relatively fast solvent-systems have been developed for TLC separation of maltodextrins and isomaltodextrins containing 1-20 glucose residues. The primary solvent contains methyl cyanide (acetonitrile)-ethyl acetate-1-propanol-water in volume proportions of 85:20:50:X, where the water component, X, is varied from 50-70 for maltodextrins and 90-100 for isomaltodextrins. Separation of the alpha-(1 --> 6) branched maltodextrins, including the two branched hexasaccharide isomers, resulting from the hydrolysis of amylopectin by alpha amylase, was achieved using 3 ascents of the solvent with 50 parts water. Separation of the alpha-(1 --> 3) branched isomaltodextrins, resulting from the hydrolysis of dextran by dextranase, was achieved using the solvent with 70 parts water. A detection technique in the nanogram range has been developed by dipping the plate into ethanol containing 0.5% alpha-naphthol and 5% sulfuric acid, followed by heating for 10 min at 120 degrees C. Saccharides appear as brown to black spots on a white background. Densitometric scanning of the TLC plate gives a linear relationship for 50 to 2000 ng of glucose. Identical plots on a weight basis are obtained for glucose, maltodextrins, and isomaltodextrins, showing that the densitometric response is independent of the saccharide structure. Thus, the relative weight percent of a series of malto- or isomalto-dextrins may be obtained by dividing the density of each saccharide by the sum of the densities of the saccharides. Malto- and isomalto-dextrins, down to dp 15-16, can be quantitatively determined by densitometric scanning of the TLC plate. These results, along with the increased sensitivity of the detection method, greatly widens the scope of the type of quantitative experiments that can be performed, which heretofore have been dependent on the use of radioactive compounds.