Structure and Functional Properties of Purple Yam (Dioscorea alata L.) Starch from China

Structural and functional properties of starch from purple yam (Dioscorea alata L.) is investigated, and starches from other three yam varieties grown in China are used for comparison. The yam starches show a variety of shapes from oval to elongated or irregular. The amylose content of four yam starches is in the range of 28.3-37.9%. The D. alata L. starch exhibits a typical B-type X-ray diffraction (XRD) pattern with a higher relative crystallinity compared with other three yam starches, which show a C-type XRD pattern. The D. alata L. starch has the higher proportion (20.6%) of long branch chain (Degree of polymerization (DP) >= 37) and the lower proportion (11.8%) of short branch chains (DP 6-12), which accounts for its higher thermal stability and lower in vitro enzymatic digestibility. This study provides useful information on the properties of purple yam starch, which would be of use for their application in preparation of foods with low enzymatic digestion.