α-amylolysis of native corn, potato, wheat and rice starch granules

A partially purified a-amylase produced by a novel Bacillus subtilis was used for the hydrolysis of native corn, potato, wheat, and rice starches at 50 degrees and 60 degrees C. The hydrolyses were carried out for 1, 2, 3 and 4 hours. For each process, the degree of hydrolysis (D.H.%) and residual starch concentrations were determined. The D.H.% values for the starches after 4 hours of hydrolysis at 50 degrees C were: 5.4% (potato), 4.8% (rice), 3.9% (wheat) and 2.3% (corn). The results after 4 hours at 60 degrees C were much higher for potato (18.5%) and wheat (14.3%), but did not change significantly for rice (4.2%) and corn (2.4%). Loss of starch was also determined after each time interval using an iodine method. Untreated and digested corn and potato starch granules were observed using a scanning electron microscope. The micrographs showed some holes and cracks (corn starch) or scratches (potato starch) on the surface of the granules.