Hydrocolloids at interfaces and the influence on the properties of dispersed systems

Although traditionally associated with thickening and gelation behaviour, food hydrocolloids also influence the properties of dispersed systems through their interfacial properties. Hence, surface-active hydrocolloids may act as emulsifiers and emulsion stabilisers through adsorption of protective layers at oil–water interfaces, and interactions of hydrocolloids with emulsion droplets may affect rheology and stability with respect to aggregation and serum separation. A review of literature evidence suggests that much of the reported emulsifying capability of polysaccharides is explicable in terms of complexation or contamination with a small fraction of surface-active protein. To support this point of view, the specific cases of gum arabic, galactomannans and pectin are considered in some detail. In mixed protein+polysaccharide systems, associative electrostatic interactions can lead to coacervation or soluble complex formation depending on the nature of the biopolymers and the solution conditions (pH and ionic strength). Protein–hydrocolloid complexation at interfaces can be associated with bridging flocculation or steric stabilisation. As well as controlling rheology, the presence of a non-adsorbing hydrocolloid can affect creaming stability by inducing depletion flocculation.