15A-13 |
Effect of homogenization and surfactant type on the rate of oil exchange between droplets in model dairy emulsions |
M. W. ELWELL, R. F. Roberts, and J. N. Coupland. Dept. of Food Science, Pennsylvania State Univ., 103 Borland Lab., University Park, PA 16802 It would be useful to supplement dairy foods with certain lipid nutrients lacking in the Western diet. Such a supplement could be in the form of an oil-in-water emulsion formulated with appropriate antioxidants that could be added to the milk, preferably before the homogenization/pasteurization step. However, any diffusion of nutrient oils from the supplement droplets to the dairy fat droplets would affect the oxidative stability of the product. The goal of the research was to determine the effects of homogenization and surfactant type of the migration of oil between droplets in a model dairy emulsion. Hexadecane or octadecane (10 wt%) was emulsified (d~0.5 µ m) in 2 wt% sodium caseinate or Tween 20 solution. These fats were selected as relatively pure lipids with similar structures and distinct melting points (in the emulsified state -0.5°C and 10.5°C respectively). The measured freezing points of the emulsified oils was measured by differential scanning calorimetry and used to track the changing composition of the lipid droplets present. When separately prepared hexadecane and octadecane emulsions were mixed, the droplets initially crystallized separately but after 200 h there was a single crystallization event in the Tween-stabilized emulsions indicating the oils had diffused between the droplets and completely mixed. In the caseinate-stabilized emulsions, there was some evidence for inter-droplet oil diffusion after 200 h but the process was much slower. When the freshly mixed emulsions were re-homogenized together, the exchange was faster and increased with number of passes through the valves. The fat in emulsions added to dairy products will mix with the diary fat already present in the system. The rate of mixing can be retarded by modifying the interfacial layer but will be accelerated if the ingredients are homogenized together. Any antioxidant system for a supplement must be designed to accommodate this.
Session 15A, Dairy Foods
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