Individual swollen starch granules under mechanical stress: evidence for deformation and volume loss

The behaviour of the individual swollen-in-water starch granule (modified waxy maize and potato) under shear stress was studied using a counter-rotating rheo-optical set-up. It was shown that the granules strongly deform under flow and eject solvent, which leads to a loss of volume. The possibility of using rheo-optics to determine the shear modulus of a single granule shear modulus was demonstrated. The difference between the two starches in the amount of solvent ejected was qualitatively interpreted from AFM and SEM images and also results available in literature. The importance of the findings for the interpretation of the flow of starch suspensions is discussed.