X-ray Diffraction for Detecting Starch Adulteration and Measuring the Crystallinity Indices of the Polymorphic Modifications of Starch

Abstract

Introduction: Starch is widely used in the food industry and biotechnology, including for manufacturing food packaging materials. Native starches from various sources exist in the form of three polymorphic modifications (A-, B- and C-types) differing in their crystal structure, which has an indirect effect on their physicochemical and technological properties.Purpose: To properly and efficiently use starch as a raw material for biotechnology, one needs to preliminarily identify its polymorphic modification and crystallinity, as well as detect and discard adulterants or substandard raw materials. X-ray diffraction is suggested to be a rapid and accurate method for solving the outlined problems.Methods: In this study, properties of commercial starch from various plant sources (corn, rice, wheat, potatoes, peas, and tapioca) were analyzed by X-ray diffraction and scanning electron microscopy.Results and conclusion: Starch of some brands was shown to be adulterated: the more expensive potato starch was replaced with cheaper corn starch. The crystallinity indices were determined for all the selected samples; the crystal structure of corn starch was found to be most highly ordered. Contrariwise, the C-type pea starch was characterized by the lowest degree of crystal structure ordering. The findings obtained in this study show that it is necessary to preliminarily determine the source of starch in order to identify its polymorphic modification, as well as physical and chemical properties by X-ray diffraction. This information will be demanded for developing the new types of functional foods and reproducing the currently used biotechnologies.