Determination of the Degree of Branching in Normal and Amylopectin Type Potato Starch with ¹H‐NMR Spectroscopy Improved resolution and two‐dimensional spectroscopy

Abstract

Abstract Starch from genetically modified potatoes was found to be highly branched compared with normal potato varieties through the use of 1 H‐NRM 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 1 H‐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)‐α‐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 1 H‐ 13 C heteronuclear spectroscopy (COSY, HMQC, 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.