30A-14

Food emulsions such as beverages, milk and desserts are important products in the food industry. During storage and handling of food emulsions, the temperature can be temporarily elevated which can result in accelerated breakdown and thus negatively impact consumer satisfaction. More research is needed to quantify the influence of temperature on instability mechanisms.

The purpose if this study was to investigate the influence of temperature on the instability of various oil-in-water emulsions.

Oil-in-water emulsion premixes were produced by blending 5wt% oil (n-decane and n-octadecane) with 2wt% aqueous surfactant solutions (Tween 20, SDS, whey protein isolate). Premixes were further homogenized using an ultrasonicator to produce emulsions with mean droplet sizes of 0.2mm. Emulsions were stored in a water bath at elevated temperatures (25, 40, 55, 70, 85ºC) for up to 2 weeks. Samples were taken at regular intervals for particle size analysis using a static light scattering technique.

All n-decane emulsions showed strongly accelerated breakdown at elevated temperatures i.e. the mean droplet size of emulsions increased from 0.2 to 0.6 mm at room temperature within 6 hours compared to a size increase from 0.2 to 3 mm at 85ºC. Small differences in final particle size was observed for emulsion stabilized with different emulsifiers (Tween 20>whey protein isolate>SDS). N-octadecane emulsions stabilized by SDS did not significantly change in size over the course of the experiment even at 85ºC, whereas n-octadecane emulsions stabilized by Tween 20 increased in size by a factor of approximately two. Results were explained in terms of temperature dependence of two independent instability mechanisms (a) Ostwald ripening and (b) coalescence.

The results indicate that the temperature-dependent rate of emulsion breakdown strongly depends on (a) the nature of the dispersed phase (b) the nature of the emulsifier. This will enable food manufacturers to formulate emulsions with increased temperature stability.