Effect of drying methods on the rheological characteristics and colour of yam flours

The effect of drying methods (sun and oven-drying) on the rheological properties and colour of amala, a thick paste from yam flour, was investigated using two varieties of yam (Dioscorea rotundata andDioscorea alata). The yam flour produced was later reconstituted to produce amala of different pasting characteristics, textural qualities and colour. D. rotundata produced amala of higher paste viscosities,and firmer gels were produced from D. rotundata than yam flour paste produced from D. alata. A higher water binding capacity (156.7%) was observed in yam flour paste produced from D. alata as comparedwith that of D. rotundata, while no significant difference was observed in the solubility index and swelling power of the two varieties. Blanching, a unit operation in yam flour processing, has a significant effect on the pasting characteristics of the reconstituted flour. It reduces the peak viscosity, holding strength, final viscosity, set back and elasticity but it has little or no significant effect on the adhesiveness, smoothness and cohesiveness of the paste. Sun and oven drying had no effect on thepasting characteristics or physicochemical properties. However, yam flour produced using sun drying method had a more elastic paste and a higher brown-index