The influence of xanthan andlambda-carrageenan on the creaming and flocculation of an oil-in-water emulsion containing soy protein

The effect of polysaccharide content on the stability of an oil-in-water emulsion (20% oil, droplet diameter 6.5 mum, pH = 7) containing soy protein (5 mg/ml) as the emulsifying agent was studied. Flocculation occurs by addition of two depletion flocculants: xanthan (0.01- 0.4%) and lambda-carrageenan (0.001- 2%). We report that in both cases the onset of flocculation occurs below the overlap polymer concentration (c* = 0.15 % for xanthan and c* = 0.58% for lambda-carrageenan). The strength of depletion interaction is dependent on such factors as polymer concentration, molecular weight and also the presence of other macromolecules. Profiles of the creaming behaviour of the sample emulsions were obtained by measuring the height of the boundary between the cream phase and the serum as a function of time for each emulsion. The result indicates that creaming kinetics is dependent on polymer concentration in a complex way. The turbidity of the serum gave an indication of whether the system was fully flocculated or contained flocks together with unflocculated droplets. At very low polymer concentrations the droplets cream individually or in small aggregates at the top of the container. At higher concentrations the droplets appear to cream as a single entity, with a sharp lower boundary separating the cream phase from a clear serum. In these emulsions and in some of the coexistent ones, there is a delay before creaming starts. The presence of the polymers at higher concentrations resulted in a stable emulsion with a very high apparent viscosity for the continuous phase and/or a strong emulsion gel network. The length of the delay phase increased with increasing concentration of both polymers.