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Optical profiling study of creaming instability of emulsions containing xanthan

T. K. BASARAN and D. J. McClements. Food Colloids and Biopolymer Lab, University of Massachusetts, Department of Food Science, Chenoweth Laboratory, Amherst, MA 01003

JUSTIFICATION: Droplet creaming is a major cause of instability in food emulsions, such as salad dressings, dairy products, beverages and sauces. Creaming is normally retarded in emulsions by adding polysaccharides that enhance the viscosity of the aqueous phase. However, under certain circumstances the addition of polysaccharides accelerates creaming instability due to depletion flocculation. It is therefore important to obtain a better understanding of the influence of polysaccharides on the creaming stability of emulsions.

OBJECTIVES: The objective of this study was to use a rapid non-destructive optical profiling method to monitor the effect of droplet size and xanthan concentration on the creaming stability of oil-in-water emulsions.

METHODS: A series of 20 wt% corn oil-in-water emulsions with different droplet diameter (d₃₂; 0.41, 0.86 and 1.32 mm), stabilized by a non-ionic surfactant (1.5 wt% Tween 20), were prepared using a high-pressure homogenizer (Rannie, Wilmington, MA). Different concentrations of xanthan (0 to 0.5 wt%) were added to the emulsions. The transmission and back scattering of near infrared light (850 nm) from the emulsions were then measured as a function of sample height and time using an optical profiling instrument (Quickscan, Beckman Coulter, CA). The creaming velocity was calculated from the change in cream layer height with time.

RESULTS: Creaming was slow at low (<0.0075wt%) and high (>0.02 wt%) xanthan concentrations, but rapid at intermediate concentrations, because of the influence of xanthan on droplet-droplet interactions and on the rheology of the continuous phase. The minimum concentration of xanthan required to promote droplet creaming increased with decreasing droplet size.

SIGNIFICANCE: This study demonstrates that optical profiling can be used to rapidly and nondestructively monitor creaming in concentrated emulsions. The application of this technique will lead to an improved understanding of the factors that influence food emulsion instability.