Food Structure


Wheat starch-water dispersions at 1:1, 1:2, 1:4, and 5 95 (w/w) starch:water ratios, representing systems with varying levels of water availability , were heated under static conditions to 75°C by microwave energy at two power settings and by convection heating. Starch granule swe lling was evaluated by light and scanning electron microscopy. Six stages in swelling were identified on the basis of s welling of small and large granules and development of an extragranular matrix. The range of swelling stages found in different locations within a sample decreased as water became more available and less limiting. At each starch:water ratio, the range of stages of Stwelling and matrix development was smaller in convection-heated samples than in microwave-heated samples, but the convection-heated samples were at more advanced stages of gelatinization than were the comparable microwave-heated samples. Each starch :wate r ratio and heating combination resulted in characteristic patterns of gelled and non-ge lled regions that could be observed visually . The microscopic and macroscopic characteristics are explained on the basis of differences in interaction with microwave radiation and subsequent heat and mass transfer.

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