Gel formation in mixtures of amylose and high amylopectin potato starch

The influence of amylopectin (Ap) (in the form of high amylopectin potato starch, HAPP) on the rheological properties of its mixtures with amylose (Am) has been studied in small-deformation oscillatory rheometry during relatively long times (6 h). The absence of HAPP granule remnants in the samples has been considered important; therefore HAPP, Am, and HAPP-Am mixtures have been prepared at 140degreesC. A higher amount of HAPP in the HAPP-Am mixture resulted in a lower value of G' of the formed systems. This trend was stronger at 10 and 8%, than at 6% total polysaccharide concentration. The rheological properties of the mixtures with the lowest amount of Am resulted in a rheological behaviour that was similar to that of HAPP at identical concentration. With increasing Am concentration in the Am-HAPP mixtures, the behaviour was comparable to pure Am. HAPP did not seem to increase the effective concentration of Am and act as a precipitator. The frequency dependence of G'(n') strongly drop with increasing Am concentration until a certain ratio of Am:HAPP was reached, approaching zero. This implied a drastic liquid-solid transition, which was clearer at higher total polysaccharide concentrations. The values of G' for pure Am increased more rapidly and at considerably lower concentrations than for pure HAPP. For HAPP the decrease in n' with increasing concentration was gradual, in three different stages. First a strong decrease in n' and W to a more or less constant value (similar to0.5) and then, at the highest concentration, n' decreased even further, and approached zero. For Am, the values of n' decreased abruptly from similar to1 to similar to0 with increasing concentration, which implies a distinct liquid to solid transition. (C) 2004 Elsevier Ltd. All rights reserved.