Effect of hydrocolloids on the rheological properties of wheat starch

Abstract

The rheological properties of 5% starch alone and in the presence of 0·5% guar, locust bean or xanthan gums were studied using a Rheotest 2 viscometer at different temperatures. The 5% starch alone exhibited non-Newtonian behaviour at 30°C, but upon gelatinization it exhibited non-Newtonian shear thinning behaviour. In the presence of 0·5% guar, locust bean or xanthan gum at 30°C itself, the flow behaviour index 'n' of starch dispersions decreased and ranged between 0·83 and 0·90 indicating shear thinning or pseudoplastic behaviour of the starch-gum dispersions. After gelatinization, the effect of these gums was higher than at 30°C and the flow behaviour index 'n' decreased from 0·64 to 0·34, 0·45 and 0·25 in the presence of 0·5% guar, locust bean and xanthan gum respectively. None of the starch or starch-gum pastes studied exhibited the yield value in the range of shear rates studied.