Sensory and Physicochemical Quality of Pounded Yam: Varietal and Storage Effects

Abstract

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. PRACTICAL APPLICATIONS 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.

Microstructure and physico-chemical bases of textural quality of yam products

“…Sensorial analysis confirmed that pounded yam prepared with Florido had very weak elasticity and smoothness in contrast to pounded yam prepared from other cultivars and particularly from Laboco (Akissoe et al, 2008). However, the instrumental measurements performed in this study failed to provide clear a Mean values (10 4 Pa) adjusted for 5 mm thickness and 5 mm width.…”

“…Observations by processors have shown that preferred varieties have the ability to form mealy, elastic and smooth dough, while other varieties have a granular, non-homogeneous dough texture (Hounhouigan et al, 2003). Sensorial analyses confirmed that the ease of moulding and the springiness of the mass were the main positive attributes of pounded yam, whereas lumpiness (lack of smoothness) was the main reason for aversion (Akissoe, Mestres, Hounhouigan, & Nago, 2008;Nindjin et al, 2006). Recently, it was reported that the elasticity of pounded yam was linked to the dry matter content of the yam tuber (Akissoe et al, 2008).…”

“…However, pounded yam prepared from Laboco had slightly lower values of adhesiveness, distance of adhesion and amylose solubility. This difficulty in assessing texture by instrumental methods is not new, and previous studies on pounded yam (Akissoe et al, 2008) or amala (Akissoe, Hounhouigan, Mestres, & Nago, 2006), which is a thick paste made from yam flour, also failed to evidence clear relationships between sensorial and instrumental texture.…”

“…Akissoe et al (2008) showed that Laboco ranked highest for elasticity and smoothness (around 13e14 for both attributes, for a maximum value of 17.5) whereas Florido ranked lowest (with less than 3 for both attributes). Observed by CLSM, cut sections of raw yam showed 100e200 mm cells (irrespective of the cultivar) almost completely filled with densely packed starch granules (Fig.…”

“…Indeed Dioscorea alata tubers are generally less friable (Egesi, Asiedu, Egunjobi, & Bokanga, 2003), but no close relationship between friability and poundability has yet been evidenced. After pounding, the resulting dough is a composite material of 21e25 g/100 g dry matter content (wet basis) (Akissoe et al, 2008) made of nearly broken cells embedded in a starchy matrix (Brunnschweiler, Mang, Farah, Escher, & CondePetit, 2006). The extent of cell disintegration appears to be linked to the firmness of pounded yam, and is greater in D. alata.…”