HOW DOES XANTHAN STABILIZE SALAD DRESSING

The creaming behaviour of model pourable salad dressings has been stud ied over a wide range of xanthan and oil phase concentrations. They we re produced by mixing a colloidally stable emulsion with xanthan solut ions. The model dressings were completely flocculated by depletion at all xanthan concentrations >0.1 g/l. Creaming behaviour was in three p hases: an initial delay phase, followed by more or less linear creamin g and finally cream compression. Delayed creaming has not been reporte d previously. It is of great practical interest, because a complete ab sence of creaming is the aim of successful dressing formulation. The l ength of the delay phase was proportional to the emulsion concentratio n, inversely proportional to the oil/aqueous phase density difference and scaled over move than four orders of magnitude with the xanthan co ncentration to powers between 3 and 4. Traditionally, the stabilisatio n of salad dressing by xanthan is explained by the yield stress of its solutions. It is shown that they do not have one, and we offer an alt ernative explanation. It is suggested that the depletion flocculation of the emulsion droplets, induced by the addition of xanthan, leads to the formation of a particle network and that it is the time-dependent yield stress of this network which stabilises the dressing.