Flour composition and physicochemical properties of white and yellow bitter yam (Dioscorea dumetorum) starches

Bitter yam (Dioscorea dwnetorwn) is an underutilized tuber crop that is rich in starch and may be potentially used as a starch source by the industry. In this study, the composition and physicochemical properties of flour and starch from white and yellow bitter yams were studied. Bitter yam showed significant variations in their proximate composition, but mineral contents were very similar. The amylose content (approx. 15%) of white bitter yam starch was slightly lower than the yellow variety (approx. 17%). Bitter yam starch granules were very small (average 5 mu m) and polygonal in shape. Starch extracts displayed the A-type crystallinity pattern with varying relative crystallinity: 22.1-28.0%. The peak gelatinisation temperature (approx. 83 degrees C) and pasting temperature (approx. 87 degrees C) were fairly high and similar for both starches. Starch peak viscosity of the white bitter yam was significantly higher than the yellow variety, which could be associated with its slightly lower amylose content. Bitter yam starch may find application in the industry where fairly high temperatures (> 80 degrees C) are frequently encountered.