Segmental mobility of polymers in starch granules at low moisture contents

The objective of this study was to determine the moisture content at which the segmental mobility of polymers within a starch granule is restricted. Common corn, waxy corn and high amylose corn starch samples were equilibrated to a final water activity of 0.15, 0.33, 0.75 or 0.97. The samples were then exposed to iodine vapor for 24 h and the color, absorption spectra and X-ray diffraction patterns were measured. Stained and unstained granules were also viewed under a bright field and polarized light microscope. The results demonstrate that successive local transitions occur within a granule with increasing moisture contents. Furthermore, the data shows that at moisture contents of about 13%, iodine is able to penetrate the granule and the resulting complex disrupts the crystalline arrangement within the granules. The differences in extent of mobility of polymers between different starch types can potentially illuminate differences in starch structure and architecture. (c) 2005 Elsevier Ltd. All rights reserved.