Changes in physicochemical and functional properties of Dioscorea rotundata yam flours in Ghana by different drying methods

Yam (Dioscorea spp.) is an important crop widely cultivated in many countries. It serves as feed for animals besides humans. Yam has many beneficial properties such as medicinal, functionalities, high nutrient content and many several uses. The methods of drying have great influence on these unique characteristics. Sun drying is the direct exposure of food material to the open sun whereas, solar drying is raising the medium for drying in a chamber to elevated temperatures by incidenting the solar radiation onto a conducting material. Solar adsorption dryer system is a combination of solar and adsorption assisted dryer systems. This study investigated the effect of different drying methods (open sun, solar, and solar-adsorption drying systems) on the drying behavior of three cultivars (pona, dente and lilii) of yam (Dioscorea rotundata). The granule size and shape affected the drying rate and functional properties. Dente with granule shapes predominantly cylindrical dried slowest compared to Pona, which dried fastest with predominantly triangular granule shapes. The lower the granule size, the higher the water binding capacity, amylose content and solubility, while amylopectin and swelling power decreased correspondingly. The solar-adsorption dried samples were more whitish than those dried by the other drying methods. Therefore, the solar adsorption method is the best recommended for drying yam cuts of Dioscorea rotundata (pona, dente and lilii) compared to the open sun and solar dryer systems. The present study has shown a strong relationship between the granule shape and rate of water removal to the surface of yam during drying.