In particulate food systems the rheological behavior is strongly influenced by particle-particle interactions. Recently, we have shown that adding a small amount of an immiscible fluid to a suspension can lead to particle bridging and network formation [1]. This effect occurs both if the secondary fluid wets the particles better or worse than the bulk fluid. The capillary bridging phenomenon can be used to stabilize particle suspensions and precisely tune their rheological properties. This allows stable food products to be created without emulsifiers or stabilizing agents, as shown here for starch and cocoa suspensions [2]. The stability and the strength of suspensions highly depends on the surface properties of the particles and the wetting and re-wetting behavior of the fluids with the particles. Even a slight shift in wetting behavior results in a strong change in flow behavior.
In oil continuous suspensions of hygroscopic particles that have been conditioned over water, the network induced by capillary bridges forms spontaneously and results in the same yield stress as if the water is added to the suspension of dry particles. This demonstrates that, in contrast to Pickering emulsions, the formation of capillary suspensions is an energetically driven phenomenon. The presence of aqueous capillary bridges between cocoa particles also improves the heat stability of model chocolate systems. Water continuous suspensions can potentially be used to design novel low fat food products. We have modified suspensions of cocoa particles in water with trace amounts of an appropriate oil to achieve texture and flow properties of regular fat continuous cocoa spreads.
[1] Koos, E.; Willenbacher, N. Science 2011, 331, 897-900.
[2] Hoffmann, S. et al. Food Hydrocolloids., 2014, 40, 44-52.
susanne.hoffmann@kit.edu
