In the case of the retrograded starch, enzymes have
to diffuse into the gel network. The diffusion rate strongly depends
on the gel concentration, which was rather high in our experiments
(50%). The limiting step of hydrolysis of granular starch, on the
other hand, is not the diffusion of the enzyme to the starch granule,
but the penetration into the granule. As starch granules are, in
fact, a mosaic of hard (crystalline) and soft (amorphous) material,
reduced susceptibility toward a-amylolysis is observed in the hard
parts of the starch granules as illustrated by Gallant et al 1992
with scanning electron microscopy