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Structure of dicarboxyl malto-oligomers isolated from hypochlorite-oxidised potato starch studied by1H and13C NMR spectroscopy

Authors
Journal
Carbohydrate Research
0008-6215
Publisher
Elsevier
Publication Date
Volume
315
Identifiers
DOI: 10.1016/s0008-6215(99)00031-2
Keywords
  • Alpha Amylase
  • Glucoamylase
  • Hpaed-Pad
  • Oxidised Starch
  • Structure
  • Ring-Cleavage
Disciplines
  • Chemistry

Abstract

Abstract The main oxidised component in hypochlorite-oxidised potato starch was isolated by anion-exchange chromatography after enzymatic hydrolysis. The primary structure of the isolated oligosaccharides was determined by 1H and 13C NMR spectroscopy, using homonuclear and heteronuclear two-dimensional techniques. The isolated pentamer and hexamer contained one glucose unit oxidised to a dicarboxyl residue. As the hypochlorite oxidation has occurred at positions C-2 and C-3 of a glucose unit, the introduced carboxyl groups caused ring cleavage between the carbons C-2 and C-3. The ring-cleaved dicarboxyl residue had glycosidic linkages on both sides, implying that this oxidation pathway does not result in depolymerisation. The vicinal coupling constant between H-4 and H-5 in the ring-cleaved dicarboxyl residue was 3.2 Hz, showing that the gauche orientations are preferred. As a result, a different bending of the starch chain is observed and is probably, therefore, one of the reasons why hypochlorite oxidation reduces the tendency to retrogradation. The p K a values (3.0) were determined from the pH-dependent chemical shifts of H-1, H-4 and H-5 of the dicarboxylic residue.

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