Native starch granules from wheat have been subjected to enzymatic depolymerization with an α-amylase from Bacillus subtilis. Crystallites made from short-chain amylose and residues from mild acid hydrolysis have been also tested. Electron microscopy, particle size analysis, DSC, and x-ray diffractometry reveal that enzymatic degradation occurs granule by granule. Gel permeation chromatography shows off the macromolecular nature of the remaining material. In contrast, acid erodes simultaneously all the granules, leading to a splitting into small particles. Crystalline fractions are completely degraded by α-amylase. These results support evidence for an active disentanglement of chains, carried out by the different subsites of α-amylase molecules. A simple mathematical treatment is proposed to explain the results of the kinetics.
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