Starch-gluten separation by shearing: Influence of device geometry

Wheat flour was separated into a gluten-enriched and a gluten-depleted (i.e. starch-rich) fraction within a conical shearing device. This paper describes the effect of the device geometry on the separation process. The gap distance between the two cones and the cone angle could be varied leading to a change in shear rate profile. The geometry influenced the aggregate formation and the following migration of the aggregates to the centre (of the cone). This study confirms that the primary aggregation is mostly influenced by shear rate, while migration of the aggregates is influenced by shear stress. However, constraining the dough by the walls of the cones also influenced the inward migration of gluten. Gluten clusters were found in all cases, but their migration to the centre only starts when they become similar in size compared to the space between upper and lower cone. It is concluded that the separation mechanism consists of three steps, rather than two. The results indicate the importance of confining the dough in between the two cones. Obviously, restriction of the growth of the gluten aggregates is a prerequisite for gluten migration. It is therefore clear that not only the shear rate but also the exact configuration of the shearing device is important for separation. This insight may lead to significant optimisation of the process of separation by shearing. The new insights were captured in a conceptual map with variables' shear rate, time and system geometry, which indicated in which regions only aggregation and in which regions only migration may be expected.