Cereal Chem. 71:282-287   |  VIEW ARTICLE


Location of Amylose in Normal Starch Granules. II. Locations of Phosphodiester Cross-Linking Revealed by Phosphorus-31 Nuclear Magnetic Resonance.

T. Kasemsuwan and J. Jane. Copyright 1994 by the American Association of Cereal Chemists, Inc. 

Amylose locations were revealed by phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy and gel-permeation chromatography. Native maize starch was cross-linked with POCl₃ at pH 12 at 25°C. The cross-linked starch was solubilized in a dimethyl sulfoxide (DMSO) solution and was separated into soluble and insoluble fractions. Gel-permeation chromatograms showed that the soluble fraction contained amylose molecules of small molecular size only. The amylopectin and large amylose molecules were cross-linked and became insoluble in the DMSO solution. The chromatograms showed no cross-linkage among amylose molecules. Phosphorus-31 NMR was used to determine the phosphate structure in the starch molecules. Chemical shift of phosphate diester (phosphate cross-linking) was between –1.0 and 1.0 ppm, and that of a phosphate monoester (phosphate derivatives) was between 4.3 and 4.9 ppm. The phosphorus-31 NMR spectra also confirmed that the amylopectin and amylose molecules cross-linked in the insoluble fraction, whereas the spectra of soluble fraction (containing amylose) displayed only a small amount of phosphomonoester derivative. The results of gel-permeation chromatography and phosphorus-31 NMR spectroscopy indicated that the amylose molecules were randomly interspersed in the starch granule instead of being in bundles.