Food Structure

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Potato starch granules were gelatinised in amylose solution to study the effect of adding amylose to a highswelling granular starch system. The effects of varying the amount of potato starch from 1-10% , added to a solution of 2% amylose, were studied by means of dynamic viscoelastic measurements and light microscopy.

The granules gelatinised in amylose solution had a lower degree of swelling than those gelatinised in water. The restricted swelling in amylose was reflected in a decrease in the complex shear modulus (G*) at 75'C. GeJatinisation in 2% amylopectin also caused a decrease in G*, but gelatinisation in 2% 0-glucose did not affect the rheological behaviour. Microstructural analysis showed that the added amylose was present outside the granules after swelling, whereas the inherent amylose from the potato starch seemed to have diffused main] y to the inner aqueous centre of the granules.

The mixed potato starch/amylose systems showed a fast gelation comparable to that of cereal starch. The results were analysed by a model predicting the shear modulus of aqueous biphasic gels. When the system is regarded as a continuous network of added amylose with dispersed potato starch granules, the results from both microscopy and rheology are in excellent agreement with the model at potato starch concentrations below 6%. As the potato starch concentration was raised, the high swelling potential of the potato starch granules led to partial disruption of the continuous amylose network. The results imply that the inherent amylose from potato starch did not contribute to the gel strength caused by the added solubilised amylose.

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