Determination of the degree of branching in normal and amylopectin type potato starch with H-1-NMR spectroscopy - Improved resolution and two-dimensional spectroscopy

Starch from genetically modified potatoes was found to be highly branched compared with normal potato varieties through the use of H-1-NMR spectroscopy. The average chain length, blue-value, and the wavelength at maximum absorptivity clearly show that the new potato varieties produce amylopectin starch. Correlation between the degree of branching as determined by H-1-NMR and starch-iodine complexation, expressed as blue-value, was good and the NMR-method gives low standard deviation. For the first time, the anomeric proton, H-1, of a (1-->4)-alpha-linked D-glucose residue and the H-1 of the glucose residue of a non-reducing end have been assigned separate chemical shifts in starch. Assignments were made as determined From two-dimensional homonuclear and H-1-C-13 heteronuclear spectroscopy (COSY, HM6C, and HMBC). The molecular weight in degraded starch and pullulan were determined by means of NMR-spectroscopy. These results were in accordance with determinations by size exclusion chromatography and with the known molecular weights of pullulan standards.