CHANGES IN RHEOLOGICAL PROPERTIES OF HYDROXYPROPYL POTATO STARCH PASTES DURING FREEZE THAW TREATMENTS .3. EFFECT OF COOKING CONDITIONS AND CONCENTRATION OF THE STARCH PASTE

The effects of different cooking conditions and concentrations on the freeze-thaw stability of hydroxypropyl potato starch (molar substitution 0.125) paste were investigated by dynamic rheological measurements and syneresis determination. The cooking conditions of the starch were chosen by taking the starch pastes at peak consistency (SP/Peak), at half breakdown consistency (SP/HB), after being held at 95-degrees-C for 15 min (SP/95-degrees-C) and after the whole pasting cycle (SP/25-degrees-C) in the Brabender Amylograph. The concentration effect was studied with the starch pastes after a whole pasting cycle at 35, 50 and 65 g kg-1. Depending on cooking conditions and concentration, the rheological responses in changes of complex modulus (G*) and phase angle (delta) of the starch pastes, with regard to the number of freeze-thaw cycles, differed considerably. This indicated that the starch pastes had undergone various structural changes during freeze-thaw treatments. With an increased extent of pasting, and with an increased starch concentration, the rheological responses indicative of the destabilisation process of the starch pastes were, in general, delayed. The number of freeze-thaw cycles required for the appearance of a peak in G*, related to the first syneresis, was one, two, five and six for SP/Peak, SP/HB, SP/95-degrees-C and SP/25-degrees-C, respectively. For the starch pastes at 35, 50 and 65 g kg-1, it was four, six and seven cycles, respectively. Based on these rheological data, it was suggested that the amount of inter-mingled amylose and amylopectin in the dispersion of hydroxypropyl starch paste is the main controlling factor, which plays a critical role in the rheological response as well as in the syneresis.