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

Proton and deuterium pulsed Nuclear Magnetic Resonance (NMR) techniques were employed to investigate the hydration properties of raw and cooked (steamed, oven baked and microwave baked) waxy (LaSoda and Pontiac) and mealy (Russet Burbank and Norchip) potato cultivars and starches. Three water components (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 to the anisotropically bound water within the potato starch granule structure. 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 (T_2Q internal) in potato cultivars and starches does not seem to be in fast chemical exchange with free and weakly bound water populations. Well defined powder patterns with a residual deuterium quadrupole splitting of about 1 kHz were observed at 22°C for raw potato cultivars and starches (17%, w/w). The quadrupole splitting, however, disappeared after cooking as a result of heat induced structural changes, 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 ¹H NMR transverse relaxation rates were observed in cooked waxy (LaSoda) in comparison with those of other potatoes.