PHYSICOCHEMICAL PROPERTIES OF STARCHES EXTRACTED FROM SWEET-POTATO ROOTS DIFFERING IN PHYSIOLOGICAL AGE

The physicochemical properties of starches from sweet potato roots dif fering in stages of development and tissue zone were examined. All of the sweet potato starch granules had both spherical and polygonal shap es by scanning electron microscopy observation. All starches gave a Ca -type X-ray diffraction pattern. Pasting properties were also characte rized by a rapid viscoanalyzer. Pasting temperatures were somewhat hig her in the peel starch and were lower in the late stage of development . Peak viscosity and breakdown tended tp be higher with increasing phy siological age. The ratio of short chains to long chains of amylopecti n determined by gel permeation chromatography (GPC) of the debranched starch was slightly higher in the early stage of development but was s imilar among different tissue zones. The distributions of chain length (degree of polymerization 6-17) of these amylopectins calculated from GPC substantially corresponded to those from high-performance anion e xchange chromatography.