Chemical composition, physical properties, and antioxidant activities of yam flours as affected by different drying methods

Yams (the tubers of the Dioscorea spp.), consumed and regarded as medicinal food in traditional Chinese herbal medicine, are seasonal foods and easily deteriorate during storage. It is of great importance to prolong the storage of yams for supplying in the off-season and without losing nutritional functionality. Three varieties of yams, Dioscorea alata (cultivars of Tai-Nung no. 2 and Ta-Shan) and D. purpurea (cultivar of Ming-Chien), were made into flours by freeze-drying, hot air-drying, and drum-drying in this report. The proximate compositions and physical properties, as well as antioxidant activities, of yam flours were determined. While drying methods showed significant effects on the moisture contents of yam flours, they had no marked effects on other components of yam flours. Colour attributes and physical properties were all affected by drying methods to different extents. While freeze-drying usually preserved more antioxidant activity of the yam flours, yam flours made of different yam varieties showed different antioxidant mechanisms.