Abstract
Transmission electron microscopy (TEM) and dynamic viscoelastic measurements were used to study the effects of varying the ratio of potato starch to amylose. Solubilised amylose was mixed with two different types of potato starch: one with starch in the form of swollen granules and the other in the form of a molecular dispersion. The total concentration was kept constant at 8% (w/w). When the level of added amylose was low, the shear modulus ( G∗) was higher for gels with swollen granules than for molecular dispersions of starch. When the level of added amylose was high, the value of G∗ was approximately the same, independent of the type of starch structure. The rheological data were evaluated by a model treating the added amylose and potato starch as phase-separated systems. The model showed that the inherent amylose of potato starch did not contribute markedly to the gel strength caused by the added amylose. Potato starch alone does not form strong gels in the time scale studied. TEM studies confirmed that the inherent and the added amylose gave rise to completely different types of structure. The added amylose had an open network structure of stiff strands. This type of structure was found in the mixed systems with added amylose and starch, but not in systems with only potato starch. Solubilised amylopectin appeared to have a droplet-like structure, often found in the form of a string of beads.
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