Morphological and structural features of amylose spherocrystals of A-type

Amylose spherocrystals of A-type were grown by mixing ethanol with hot aqueous solutions of short chain amylose followed by slow cooling to 4 degrees C. The spherocrystals which had a diameter of the order of 10 microns were observed by scanning electron microscopy and analysed by X-ray diffraction. They were also cross-sectional for transmission electron microscopy and electron diffraction investigation. These techniques showed that each spherocrystal consisted of an assembly of thin elongated single crystal-like domains of A-type amylose radiating from the centre of the spherocrystal. In each of these domains, the chain axis of amylose was found to be aligned with the long axis of the domain, in agreement with the overall positive optical birefringence observed for the spherocrystals. The spherocrystals which were rather fragile broke easily along the boundaries of the crystalline domains. This could explain the susceptibility of these structures to alpha-amylase digestion.