Platelet Nanocrystals Resulting from the Disruption of Waxy Maize Starch Granules by Acid Hydrolysis

Abstract

Colloidal aqueous suspensions of starch nanocrystals were prepared by submitting native granules from A-type amylopectin-rich waxy maize to a hydrochloric acid hydrolysis. The insoluble residue contains polydisperse and more or less individualized platelet nanocrystals corresponding to the lamellae formed by the association of amylopectin side branches into parallel arrays of double helices. After 2 weeks of hydrolysis, 5-7 nm thick lamellae still connected by alpha(1-->6) linkages were seen edge-on using transmission electron microscopy. As the hydrolysis progressed up to 6 weeks, more alpha(1-->6) branching points located in the inter-lamellar areas were severed and the platelets were thus observed in planar view. Despite a variety of shapes, characteristic geometrical features of the nanocrystalsa were recognized, such as marked 60-65 degrees acute angles and constituting parallelepipedal blocks with a length of 20-40 nm and a width of 15-30 nm. X-ray and electron diffraction showed that these nanoplatelets retain the crystalline A-type of the parent granules.