Differences in rheological behavior between normal and waxy corn starches modified by dry heating with hydrocolloids

The differential influence of dry heat treatment on the rheological behavior of normal and waxy corn starches with three types of hydrocolloids (xanthan, sodium carboxymethyl cellulose, and sodium alginate) was investigated. Dry heating with hydrocolloids significantly increased the apparent viscosities of both the normal and waxy corn starches. The apparent viscosity of the heated waxy-corn-starch-xanthan mixture was up to 10 times that of the unheated mixture at shear rate of 0.01 s(-1). Compared to untreated starch, the values of G' and G for all the samples significantly increased and the tan delta values decreased, reflecting increased viscoelasticity. Dry heating with xanthan rendered a more profound effect on the tand values of waxy-corn-starch pastes (from 0.49 to 0.26) than dry heating with CMC or alginate. Confocal laser scanning microscopy images of the samples showed that xanthan could penetrate the interior of waxy-corn-starch granules. However, it was mainly absorbed onto the surface of normal-corn-starch granules.