ABSTRACT
The water dynamics in gels made from native wheat starch, control (alkali-treated) starch, and hydroxypropylated starch were studied using 1H NMR relaxometry. Transverse relaxation studies showed that at least two domains of water exist in the starch gel, one with a T2 of 0.5–8 msec and one with a T2 at 8–200 msec. For starch gels held at 5°C for up to 15 days, the peak T2 of both regions decreased with time for gels made from native starch, but not for those made from hydroxypropylated starch. Changes in integrated signal in each region suggests that water migrates out of the lower T2 domain during retrogradation. Gels made from isolated amylose had a single, relatively mobile water domain, with T2 dependent on gel concentration. This fraction did not change during storage at 5°C. Granule-rich gels showed two water domains, one with a T2 range similar to that for amylose gels, which varied over time and were thermally reversible. During storage, most significant changes occurred in the relatively low T2 region associated with granule remnants. These studies show that, in addition to changes in starch during retrogradation, water dynamics are also affected by recrystallization and chemical modification of starch molecules.
