Internal structure of normal maize starch granules revealed by chemical surface gelatinization

Normal maize starch was fractionated into two sizes: large granules with di ameters more than 5 mum and small granules with diameters less than 5 mum. The large granules were surface gelatinized by treating them with an aqueou s LiCl solution (13 M) at 22-23 degreesC. Surface-gelatinized remaining gra nules 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 su rface gelatinization, were subjected to scanning electron microscopy, iodin e potentiometric titration, gel-permeation chromatography, and amylopectin branch chain length analysis. Results showed that the remaining granules ha d a rough surface with a lamella structure. Amylose was more concentrated a t the periphery than at the core of the granule. Amylopectin had longer lon g B-chains at the core than at the periphery of the granule. Greater propor tions of the long B-chains were present at the core than at the periphery o f the granule.