Starch granules involve various amounts of fatty acids as “Fat by Hydrolysis” in different plant sources. These fatty acids are possibly embraced in amylose component and concerned in affecting some properties of the granules, but it is not yet clear through what process they are embraced into the granules in vivo.
In this study, starch samples differing in granular size were prepared from sweet potato tubers of different maturity, and were studied on quantative and qualitative changes in the embraced fatty acids and transitions of some chemical and physical properties with the development of granular size.
Each X-ray diffraction pattern of the samples of small granules was clearly characterized by the respective season when the tubers were harvested. This suggests that the small granules have developed just before the harvest. Such starch granules in earlier stage of development were shown to be higher in contents of both amylose and the embraced fatty acids, the major component of which was palmitic acid. Both contents decreased with the development of granules, while the quantity of oleic acid incorporated was found to be approximately constant throughout the developing duration.
These results suggest that palmitic acid contributes to the occurrence of starch granules in vivo, because incorporation of palmitic acid into amylose may result in repressing the free movement of amylose molecules and in bringing about formation of amylose gel.