Influence of water, temperature and sucrose on dynamics in glassy starch-based products studied by low field 1H NMR

In this study, the influence of both water content and temperature on the mobility of glassy starch-based matrices (starch alone or mixed with sucrose at the ratio 0% to 20% db) were studied using time domain 1H NMR. The 2nd moment M2, and transversal relaxation time T2∗ were used to study the molecular mobility of the rigid and mobile fraction of the NMR signal, respectively.The molecular mobility of the protons constituting the samples increased with water content (up to 13% wb) at all temperatures. For a given water content, both rigid and mobile protons exhibited a lower mobility in the presence of sucrose. When mobility characteristic parameters, M2 second moment values and spin–spin relaxation times T2∗, were normalized by Tg, i.e plotted versus Tg/T, the effect of water was no longer visible whereas the effect of sucrose remained marked. The temperature increase induced an increase in both rigid and mobile protons mobility. Whereas no clear change could be observed on the rigid protons mobility around the glass transition temperature the mobile fraction exhibited a marked mobility change in that temperature range.