Crystalline structures of the main components of starch

Abstract

• Crystalline structures present in starches are hexagonal or/and orthorhombic. • A-Type starches contain an orthorhombic structure. • B-type starches contain a hexagonal structure. • A complete indexing of the orthorhombic and hexagonal structures was done. This work reports an X-ray diffraction analysis of the crystalline phases present in starch. Crystallographic studies using Grazing Incidence X-ray Diffraction (GIXRD) were carried out for defatted isolated starches from amaranth and avocado pits. These studies confirm previous ones that reported the occurrence of the A-type orthorhombic and B-type hexagonal structures, in which a partial indexing of the diffraction peaks recorded was reported for the orthorhombic structure. In contrast, the indexing of the diffraction pattern of the hexagonal structure has not been previously reported. The present study provides the identification and a complete indexing of the orthorhombic and hexagonal structures present in starches, which would facilitate the correct identification of these two crystalline structures in materials where starch is present.