Birefringence of Amylose and Amylopectin in Whole Structural Starches

Abstract

THE view is current that unbranched amylose chains are responsible for the anisotropy of structural and fractionated starches^1–3. (A review of this subject by S. Peat⁴ should be consulted.) This view has been influenced by the method of investigation employed. Thus the evidence from X-ray powder diagrams does not entirely coincide with that from the study of optical birefringence. Perfectly dry starches are stated^5,6 to show an amorphous powder diagram though they still exhibit birefringence. The kind of product also matters. Thus, fractionated amylose may be deposited in a micro-crystalline form⁴, whereas amylopectin remains amorphous or statistically isotropic. But fractionation procedures may also determine physical states, so that no direct conclusion can be drawn concerning the anisotropy of amylopectin in raw structural starches. Thirdly, interpretation may also be prejudiced by theoretical assumptions regarding the structure of the branched high polymer. Thus the random branching postulated by Meyer¹ would offer a resistance to crystallization absent from the models proposed by Staudinger⁷ or Haworth⁸.