CREAMING OF CONCENTRATED OIL-IN-WATER EMULSIONS CONTAINING XANTHAN

Time-dependent creaming profiles are reported for mineral oil-in-water emulsions (18 vol% oil, 2 wt% Tween 20) containing various amounts of the microbial polysaccharide xanthan. Data were obtained by the ultrasound velocity scanning technique at 30-degrees-C in samples of height 250 mm. In emulsions without added salt, the major instability at low xanthan concentrations (approximately 0.02 wt%) is the rapid development of a serum layer near the bottom of the sample, whereas at higher concentrations (0.05-0.2 wt%) destabilization is associated with the development of a cream layer (60-70 vol% oil) near the top. Emulsions containing 0.05 mol/dm3 NaCl do not exhibit such clear serum separation at low xanthan concentrations, but are much less stable to creaming at higher concentrations (approximately 0.5 wt%). The use of the Urick equation to relate ultrasound velocity to oil volume fraction is found not to be valid for these emulsions.