Structural and hydration studies of waxy and mealy potato starch cultivarsby deuterium, carbon-13 CP-MAS/MASS NMR, and electron microscopy

Proton and deuterium pulsed Nuclear Magnetic Resonance (NMR) techniques wer e employed to investigate the hydration properties of raw and cooked (steam ed, oven baked and microwave baked) waxy (LaSoda and Pontiac) and mealy (Ru sset Burbank and Norchip) potato cultivars and starches. Three water compon ents (T-2Q internal, T-2A medium and T-2B long component) were resolved in potato cultivars and starches. The first water component T-2Q is assigned t o the anisotropically bound water within the potato starch granule structur e. The T-2A corresponds to trapped water, whereas, the T-2B-long component is assigned to the average between weakly bound and free water populations. The anisotropically bound water (T2Q internal) in potato cultivars and sta rches does not seem to be in fast chemical exchange with free and weakly bo und water populations. Well defined powder patterns with a residual deuteri um quadrupole splitting of about 1 kHz were observed at 22 degrees C for ra w potato cultivars and starches (17%, w/w). The quadrupole splitting, howev er, disappeared after cooking as a result of heat induced structural change s, and only rapidly, isotropically reorienting water remained. The T-2A and T-2B values were also significantly affected by the cooking method. The T- 2B values of cooked potatoes were shorter than those of raw potatoes. Heat induced structural changes were reflected in the shorter T-2B value of the cooked and crushed potatoes. Lower average H-1 NMR transverse relaxation ra tes were observed in cooked waxy (LaSoda) in comparison with those of other potatoes.