SEPARATION AND NMR STRUCTURAL CHARACTERIZATION OF SINGLY BRANCHED ALPHA-DEXTRINS WHICH DIFFER IN THE LOCATION OF THE BRANCH POINT

A series of singly branched a-dextrins with dp greater than or equal t o 5 was prepared by treating amylopectin with an alpha-amylase (Termam yl) and then with beta-amylase. The dextrins were separated by gel fil tration chromatography and the composition of the fractions was checke d by HPAEC. Each fraction gave essentially a single peak by HPAEC but NMR spectroscopy indicated that only the fraction corresponding to dp5 consisted of one compound. The fractions corresponding to dp6, 7 and 8 were found to be mixtures of isomers. Three isomers of dp6 were sepa rated by reversed phase HPLC and were characterised by NMR spectroscop y. The isomers were identified as 6(2)-alpha-maltotriosyl-maltotriose, 6(3)-alpha-maltosyl-maltotetraose and 6(2)-alpha-maltosyl-maltotetrao se. H-1 and C-13 NMR parameters of these compounds and of dp5, 6(2)-al pha-maltosyl-maltotriose, are discussed in relation to the linkage pat tern of the different glucose units and compared with similar paramete rs in the linear maltodextrins. (C) 1998 Elsevier Science Ltd. All rig hts reserved.