Details of the Crystalline Ultrastructure of C-Starch Granules Revealed by Synchrotron Microfocus Mapping

A microfocus synchrotron wide-angle diffraction mapping experiment was used to analyze the crystalline microstructure and the polymorphism of a series of C-starch granules from smooth pea. In these specimens that globally contained 60% of A-phase and 40% of the B-allomorph, it was found that the two phases were present in each granule. The A-allomorph was located essentially in the outer part of the granules whereas the B-phase was found mostly at their center. In the A-component, the diffraction diagrams were always poorly oriented fiber patterns with the fiber axis systematically oriented toward the center of the granule. On the other hand, in the B-center, only powder diagrams could be observed whereas in middle zones of the granules, the B-component was much better oriented than the A-component.