1H NMR studies of molecular mobility in wheat starch

Pulsed H-1 NMR was used to determine moisture content and molecular mobility of wheat starch suspensions at water activity (a(w)) values between 0. and 0.93. Moisture determination by NMR agreed well with gravimetric determinations (R-2=0.99), Transverse proton relaxation (T-2) of the systems were identified using single pulse and CPMG experiments. T-2 associated with starch molecules increased linearly from 7.1 to 10.1 mus as a(w) increased from 0 to 0.93, due to plasticizing effects of water. T-2 associated with water molecules showed a linear increase up to a(w) of 0.69. Results indicated that H-1 NMR could be employed to determine moisture content of starch suspension and to identify and quantify the molecular motion of starch chains and water molecules of starch suspensions at low moisture levels. (C) 2003 Elsevier Science Ltd. All rights reserved.