Characterization of water mobility and distribution in low- and intermediate-moisture food systems

The mechanism of water uptake in low moisture cereals and cookies has been studied by NMR relaxometry and solid imaging technology implemented on a lo w-resolution benchtop NMR spectrometer. A comparison between classical MRI and SPRITE imaging are also presented to highlight the benefits of each tec hnology. The spin lattice (T-1) and spin spin (T-2) relaxation times, the 1 D and 2D SPRITE imaging, were determined on Smacks(TM), corn flakes, chocol ate chips cookies, soft caramel candies with a chocolate creme filler, and corn starch/water systems. The Smacks(TM) and corn flakes were studied base d on the soaking time in milk, and the results showed that T-1 and T-2 decr eased in the first 20 sec of soaking and then increased with the soaking ti me. For Smacks(TM) stored at different relative humidity, T-1 decreased dur ing the first day of storage and then was relatively constant over storage time indicating that the system reached an equilibrium. 1D SPRITE profiles indicated an increase in signal intensity over storage time for cookies in 58% RH. However, the moisture uptake was insignificant indicating that the water mobility (and not the amount of water) changed due to various chemica l interactions in the system (hydrogen bonding, starch retrogradation, glas sy/rubbery equilibrium). The T-1 and T-2 of corn starch/water systems decre ased as the concentration in starch increased and temperature increased fro m 30 degrees C to 60 degrees C. However, for temperatures higher than 60 de grees C, the relaxation times increased showing more mobility and flexibili ty of the polymer chains during gelatinization. (C) 2000 Elsevier Science I nc. All rights reserved.