Abstract:

After treatment with acid, amylase or glucoamylase, starches from yam (Dioscorea opposita Thunb.) tuber and
bulbil were characterized for physical and chemical properties by scanning electron microscopy (SEM), X-ray diffraction
and rheometer. The results showed that the native starch granules from yam tuber and bulbil exhibited a complete oval
shape with a smooth surface and no cracks. Yam starches were degraded by enzymatic and acid treatments, and the surface
of acid-treated starch granules was more severely damaged. The crystallinities of native, acid- and enzymatically-treated
bulbil starches were 32.02%, 27.02% and 31.13%, respectively, while those of native, acid- and enzymatically-treated tuber
starches were 34.32%, 29.27% and 33.55%, respectively. The transmittance and retrogradation percentage of starch paste
showed that the native starch from yam bulbil could be aged most easily. Rheological characteristics illustrated weak gel
properties of yam starches.

Key words: yam tuber, yam bulbil, scanning electron microscopy, X-ray diffraction, rheological properties