GELATION AND RETROGRADATION OF CONCENTRATED STARCH SYSTEMS .2. RETROGRADATION

Concentrated starch gels were prepared by heating starch suspensions a t rest. Large deformation properties of these gels were studied by com pressing cylindrical samples between parallel plates. It was observed that the properties of concentrated starch gels at large deformations depend on the age of the gels and the type of starch. The mechanical p roperties of the gels are related to their structure, consisting of pa rtly swollen, irregularly shaped granules with a thin amylose matrix g el between them. Observed changes in the Young's modulus, and in the f racture stress and strain during storage are ascribed primarily to the increase in stiffness of the swollen granules. The rate at which the mechanical properties change during storage is at least partly affecte d by the number of entanglements between the starch molecules or the n umber of chemical cross-links present.