1H NMR studies of molecular mobility in potato starch

NURIA ACEVEDO; CAROLINA SCHEBOR; MARÍA DEL PILAR BUERA

Alimentos Ciencia e Ingeniería

Universidad Técnica de Ambato, Facultad de Ciencia e Ingeniería de Alimentos

Lugar: Ambato; Año: 2007 vol. 16 p. 99 - 100

1390-2180

Pulsed 1H NMR was used to determine molecular mobility of water and polymers in freeze-dried potato starch samples in relation to the sorption properties of the system in a range of 0.43-0.98 water activity (aw). Water sorption data were determined isopiestically at 25°C. Thermal transitions were determined by differential scanning calorimetry. Molecular mobility was related to protons relaxations, and it was analyzed by 1H NMR measuring spin-spin relaxation times (T2). The analysis of rapidly relaxing components following a single 90º pulse experiments (FID) was used to assess the mobility of polymers and water molecules strongly associated to the polymers. The slow relaxing component (related to the most mobile water molecules) was determined by CPMG method. The FID analysis showed a single T2-FID which increased with the increase in RH and temperature; however a clear change in the T2-FID values could not be identified around the glass transition temperature (Tg). The CPMG analysis gave a short component (T2-1) in the order of milliseconds attributed to the “multilayer” water molecules and a long component (T2-2) which value increased with increasing water content. This increase was independent on temperature and on the physical state of the sample. The proportion of protons of the long component, measured by the signal amplitude, (A2-2), also increased with increasing water content, suggesting that it is directly related to the mobility of water. 1H NMR could be employed to determine the water states of freeze-dried potato starch samples and relate them to the different regions of the sorption isotherm.