Pasting and Functional Properties of Chemically Modified Yam ( Dioscorea rotundata) Starches

Abstract

For the present study, we evaluated the effect of the concentration of modifying agents and reaction time on functional properties of yam (Dioscorea rotundata cv hawthorn) starch modified by oxidation and phosphatization. For oxidation was used a sodium hypochlorite concentration of 0.5 and 1.5 g/100 g starch (b.s.) and reaction time of 1 and 1.5 h; and for phosphating, sodium trimetaphosphate of 2 and 3 g/100 g starch (b. s.) and reaction time of 2 and 3 h. The pasting properties were determined during heating and cooling cycles (viscoamilograms) using a rotational rheometer (Anton Paar). The increase in modifying agent concentration and reaction time significantly reduces peak viscosity and setback by up to 98.53 and 95.62% respectively, while the pasting temperature decreases with both factors by up to 2.5% for both modifications. Functional properties such as swelling power, capacity and water absorption rate were affected over time in phosphating, but not in oxidation. Oxidation causes depolymerization and phosphating make starch granules more resistant to shearing, reducing viscosity when functional groups are introduced during modifications. The increased concentration of modifying agents and reaction time decrease the peak viscosity and setback of yam starch, but only time affects other properties, allowing its uses in the food industry to be extended. Keywords: