CHANGES IN RHEOLOGICAL PROPERTIES OF HYDROXYPROPYL POTATO STARCH PASTES DURING FREEZE-THAW TREATMENTS .1. A RHEOLOGICAL APPROACH FOR EVALUATION OF FREEZE-THAW STABILITY

A fundamental rheological method was used to study the freeze-thaw stability of hydroxypropyl potato starch pastes. The effect of the number of freeze-thaw cycles on the changes in complex modulus (G*) and phase angle (delta) during heating of the thawed starch pastes was evaluated by comparing the rheological measurements with the measurements of syneresis at different centrifugal forces. The centrifugal forces influenced the detection of the first syneresis as well as the extent of syneresis, with regard to the number of freeze-thaw cycles. When starch pastes exhibited syneresis, the G*formed a distinctive peak during heating at 52.5-53.8C. The magnitude of the peak became bigger with number of freeze-thaw cycles. Furthermore, the results of this rheological method give information on the destabilization process and provide a simple method for detection and prediction of the extent of freeze-thaw stability of starch paste. With this method, the effect of the storage period at - 20C, and the freezing rate, on the extent of freeze-damage of starch pastes could be investigated successfully.