Internal Structure of Normal Maize Starch Granules Revealed by Chemical Surface Gelatinization

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Abstract
Normal maize starch was fractionated into two sizes: large granules with diameters more than 5 μm and small granules with diameters less than 5 μm. The large granules were surface gelatinized by treating them with an aqueous LiCl solution (13 M) at 22−23 °C. Surface-gelatinized remaining granules were obtained by mechanical blending, and gelatinized surface starch was obtained by grinding with a mortar and a pestle. Starches of different granular sizes and radial locations, obtained after different degrees of surface gelatinization, were subjected to scanning electron microscopy, iodine potentiometric titration, gel-permeation chromatography, and amylopectin branch chain length analysis. Results showed that the remaining granules had a rough surface with a lamella structure. Amylose was more concentrated at the periphery than at the core of the granule. Amylopectin had longer long B-chains at the core than at the periphery of the granule. Greater proportions of the long B-chains were present at the core than at the periphery of the granule.