Sensory and physicochemical quality of pounded yam: varietal and storage effects

Tubers from nine yam cultivars (Dioscorea rotundata, Dioscorea alata) collected in two different growing areas of Bénin were stored for up to 5 months. Pounded yam was prepared from tuber samples each month and evaluated for their sensory and physicochemical attributes in order to assess the effect of tuber storage on suitability for processing into the product. Irrespective of the initial tuber dry matter content, the dry matter content of pounded yam remained almost constant with a mean value of 23% (wet basis). The general preference increased linearly with "elasticity" and "smoothness" (r² = 0.945) of the pounded yam. A principal component analysis coupled with a hierarchical classification produced five sample classes. Pounded yam prepared from cultivar Florido provided a single class, with low values for "elasticity" and "smoothness." This was opposite to the class of cultivar Laboco. Pounded yam samples from Gnidou were grouped in a class characterized by a low level of sweetness. The sweetness and elasticity of the product increased slightly when the yam tubers were stored, but this was not enough to raise the level of acceptability. The chemical and textural characteristics of pounded yam were poorly correlated with the sensory attributes. The elasticity of pounded yam appeared linked to yam tuber dry matter content. This work showed that the quality of pounded yam mainly depends on the cultivar and not on the production area. It confirmed that high-yielding cultivars, such as Florido and Gnidou, give pounded yam of poor or barely acceptable quality. These cultivars should be mainly held in store for other end uses. Storing tubers induces few changes in their ability to give a good pounded yam. We observed a slight improvement of the elasticity and sweetness of pounded yam after tuber storage, but this was insufficient to greatly improve the pounding ability of the less preferred cultivars. Tuber storage was nevertheless never detrimental for quality, and farmers should take advantage of this, storing to sell at higher prices, outside the harvesting period.