Emulsions

Food emulsions, including margarine, ice cream, mayonnaise and salad dressing, represent another economically important system observable by MRI. The potential for measurement by MRI of oil/water ratios in separated salad dressings emerged early on (Heil, et al., 1990). Manufacturers of these products and of non-food emulsions must understand the affect of emulsifiers on phase separation of emulsions, and control particle size distribution. Magnetic resonance imaging can quantify phase separation kinetics by exploiting relaxation and chemical shift differences, and estimate particle size through quantifying restriction of diffusion.

In contrast to previous methods, MRI techniques for rapidly determining relaxation rates of oil and water permit non-invasive measurement of separation kinetics of emulsions. Many previous methods for quantifying phase separation require disturbing the emulsion and thereby accelerating separation (Dickinson and Stainsby, 1988). Ultrasound techniques, while non-invasive, require the absence of air bubbles, often present in homogenized samples. Ultrasound offers no spatial selectivity and demands separate measurements at each point (Povey, 1987). A technique developed for rapid Ti relaxation rate determination (Canet, et al., 1988; Fanni, et al., 1989) proved useful for rapid determination of oil and water volume fractions. When modified with imaging techniques, the technique offered the volume fraction ratio at all points simultaneously along a vertical emulsion profile (Kauten, et al., 1991). The apparent Ti at each point along the profile obeyed the equation:

Ti obs Ti water Ti oil with <)> denoting the volume fraction. Using this method, Pilhofer et al. (1993) observed rates of separation of milkfat/water emulsions and compared the data to predictions from Stoke's law,

Proton Sodium Sodium

Protein

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