WATER ORGANIZATION AND MOLECULAR MOBILITY IN MAIZE STARCH INVESTIGATED BY 2-DIMENSIONAL SOLID-STATE NMR

The molecular mobility of polysaccharide chains and the water organization in maize starch forms A and B were investigated with the recently developed 2D H-1-C-13 heteronuclear wideline separation (WISE) method of solid-state NMR spectroscopy. Proton lines of starch yield information about the molecular motion. No evidence for molecular motion of the polysaccharide chains on a time scale faster than microseconds was found. From the WISE spectra measured with a short mixing time it was estimated that 28% of the water present was bound to the polysaccharide chains. in forms A and B. It was found that there is no preference for water to bind to particular sites of the glucose rings. Comparison of WISE spectra obtained with different mixing times tm revealed differences in water organization between the starch forms. From the rate of the spin diffusion process active during t(m) it was concluded that the molecular mobility of water in form A is higher than in form B. This explains the lower gelation temperature of A-form starch.