14B-34

Comparison of optical and ultrasonic profiling techniques for monitoring creaming instability in food emulsions

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: Many food emulsions stabilized by proteins contain high mineral contents, e.g., infant formulations, sports drinks, and nutritional beverages. Minerals can adversely influence the stability and physicochemical properties of these products because of ion binding and electrostatic screening effects. The design of protein-stabilized emulsions that remain stable in the presence of high mineral contents depends on the availability of analytical techniques to nondestructively monitor the impact of minerals on emulsion stability.

OBJECTIVES: The objective of this study was to develop and compare rapid non-destructive methods, based on ultrasonic and optical imaging, to monitor the influence of minerals on the creaming stability of protein-stabilized emulsions.

METHODS: Corn oil-in-water emulsions (10.0 wt%; d₃₂=1.0 mm) stabilized by 0.5 wt% whey protein isolate (WPI) were prepared with a range of calcium chloride concentrations (0-10 mM). The ultrasonic velocity of the emulsions was measured as a function of sample height and time (LeCroy 9310A, Chestnut Ridge, NY). The transmission and back scattering of near infrared light (850 nm) were also measured (Quickscan, Beckman Coulter, CA) as a function of sample height and time. The resulting ultrasonic and optical profiles were converted into concentration-distance profiles using empirical equations.

RESULTS: Accelerated creaming was observed in the emulsions when the CaCl₂ concentration exceeded 2 mM, which was attributed to droplet flocculation caused by ion binding and electrostatic screening. The optical profiling technique was most suitable for studying regions where droplet concentrations were relatively low (<1%), whereas the ultrasonic profiling technique was more suitable for studying regions where droplet concentrations were relatively high (>1%).

SIGNIFICANCE: This study demonstrates that ultrasonic and optical profiling techniques are suitable for nondestructively monitoring creaming in optically opaque systems. The parallel application of these two techniques will lead to an improved understanding of the factors that influence creaming in food emulsions.