α-Amylolysis of native potato and corn starches – SEM, AFM, nitrogen and iodine sorption investigations

Scanning electron microscopy (SEM), atomic force microscopy (AFM), as well as iodine and nitrogen sorption measurements were applied to investigate potato and corn starch granules surface after an action of Bacillus subtilis α-amylase. The SEM images revealed holes and pits (corn starch) or scratches (potato starch) on the surface of modified granules. These results were confirmed by AFM investigation which showed the presence of depressions of approximately 121 nm in diameter. Structure of the surface was not uniform. It consisted of small particles, amylopectin blocklets, of approximately 20 nm in diameter. They became more distinctive after α-amylolysis. Values of iodine binding capacity (IBC) obtained for hydrolyzed granules were lower than for native ones which indicated that the amylose and amylopectin chains building their surface were shortened. Specific surface area, volume and average diameter of mesopores increased for both starches after α-amylolysis.