State of water in starch-water systems in the gelatinization temperature range as investigated using dielectric...

The dielectric response of native wheat starch-water slurries containing 5-60% starch (w/w) was measured in the frequency range of 0.2-20GHz after heating the slurries to 7 different temperatures between 25 and 90°C for 30min. Three relaxations, with relaxation time range of 4-9ps, 20-25ps and 230-620ps at 25°C, were identified from the dielectric spectra of starch slurries. The fastest relaxation process (4-9ps) was attributed to bulk water while the two slower relaxations were attributed to the confined water molecules present in the starch-water system. The amount of water exhibiting the slowest relaxation (230-620ps) was calculated to be 0.08-0.16gwater/g starch, which was close to the monolayer water associated with wheat starch. Mobility of bulk water was significantly reduced (P<0.001) upon gelatinization at low starch concentration (10% starch), but remained unaffected at higher starch concentrations. The mobility of two slower relaxing water species was not significantly influenced (P>0.19) by gelatinization at all starch concentrations.