Rheological and viscoelastic properties of corn starch suspension modified by hydrothermal process: Impacts of process intensification

Rheological properties of starch suspension and particle size distribution of treated starch granules under the same conditions (2 bar and 20 min) by direct vapour-heat moisture treatment (DV-HMT), Reduced-Pressurized Heat Moisture Treatment (RP-HMT) and Instantaneous Controlled Pressure Drop Process (DIC) were investigated. DV-HMT and RP-HMT were compared to DIC process in order to determine the role of the vacuum pressure steps before and after injection of live steam on the starch powder. For all treated starches an increase of the particle size of granules was observed, a reduction of the consistency index and of the conservative modulus, compared to the untreated one. This difference becomes so important with increasing of process intensification. Relaxation spectra evaluated from the generalized Maxwell model implied a drift to shorter relaxation time for treated starch suspension than the native one. A decrease in peak intensity H(λ) of relaxation spectra with increase of intensification of processes was observed which conclude that the modified starch suspension moving away from a stable state like gel according to the following order DV-HMT < RP-HMT < DIC. The effect of DIC process seems to be more intense than the two other treatments. This difference can be attributed to the mechanical effect induced by the abrupt decompression towards vacuum after treatment.