Effect of dissolution and partial hydrophobic coating on floating of crystalline particles

Food powder reconstitution is frequently compromised by powder floating. Although particle floating has been studied for many years, several common properties of food powders have not been considered. To elucidate the effect of dissolution and hydrophobic surface defects, floating of pure and partially coated spherical sucrose beads was analysed. It was found that floating of soluble particles is characterised by a gradual increase of immersion depth which proceeds until the particle is fully engulfed and detaches from the interface. The duration of floating depends on initial floating position, immersion and dissolution velocity. Floating of partially coated beads is additionally affected by contact line pinning at coating material. Theoretical predictions, based on force balance analysis did not reflect the observed floating behaviour indicating that dissolution requires consideration of further factors. Particularly the observed formation of a convection current, which creates an additional downwards drag, is suggested to play a decisive role. (c) 2021 Elsevier B.V. All rights reserved.