Thermal Properties and Dynamic Rheological Characterization of Dioscorea Starch Gels

Abstract

Yam (<i>Dioscorea</i>. sp.) is an edible starchy tuber with potential for being a commercial source of starch for industrial purposes, but yam starch is underutilized. The dynamic oscillatory and thermal properties of yam starches from sixteen varieties each of <i>Dioscorea. rotundata</i>, <i>Dioscora. alata</i>, <i>Dioscorea. bulbifera</i> and one variety of <i>Dioscorea. dumetorum</i> from Nigeria were studied to determine their potential for industrial utilization. The storage modulus, loss modulus, damping factor and complex viscosity as a function of frequency (ω) of the <i>dioscorea</i> gels, as well as the onset temperature (<i>T_o</i>), peak gelatinization temperature (<i>T_p</i>), end of gelatinization (<i>T_C</i>), and gelatinization enthalpy of the starches were determined by standard procedures. Results showed that all the <i>dioscorea</i> starches showed a typical elastic behavior with the magnitude of G' greater than G″ while tan δ < 1 in all varieties. Thus, the starch gels were more elastic than viscous. All the starch gels exhibited shear thinning characteristics and showed frequency (ω) independence characteristics of weak gels. <i>D. rotundata</i> varieties had the lowest ∆<i>H_gel</i>, while <i>D. bulbifera</i> varieties had the highest. The diversity of the visco-elastic and thermal properties of the yam starch gels from different varieties and species can be an advantage in their utilization in both food and non-food industries.