Tribology of Swollen Starch Granule Suspensions from Maize and Potato
The tribological properties of suspensions of cooked swollen starch granules are characterised for sys-tems based on maize starch and potato starch. These systems are known as granule ‘ghosts’ due to therelease (and removal) of polymer from their structure during cooking. Maize starch ghosts are less swollenthan potato starch ghosts, resulting in a higher packing concentration and greater mechanical stability.In a soft-tribological contact, maize ghost suspensions reduce friction compared to the solvent (water),generate bell-shaped tribological profiles characteristic of particle entrainment and show a marked con-centration dependence, whereas potato ghost suspensions exhibit lubrication behaviour similar to water.Microscopy analysis of the samples following tribological testing suggests that this is due to the rapidbreak-up of potato ghosts under the shear and rolling conditions within the tribological contact. A reduc-tion in the small deformation moduli (associated with a weak gel structure) is also observed when thepotato ghost suspensions are subjected to steady shear using parallel plate rheometry; both microscopyand particle size analysis show that this is accompanied by the partial shear-induced breakage of ghostparticles. This interplay between particle microstructure and the resultant rheological and lubricationdynamics of starch ghost suspensions contributes to an enhanced mechanistic understanding of texturaland other functional properties of cooked starches in food and other applications.