Food Lipids: Chemistry, Nutrition, and Biotechnology

creaming and sedimentation in emulsions and for predicting the long-term stability
of food emulsions.
F. Emulsion Rheology
The rheology of an emulsion is one of its most important overall physical attributes
because it largely determines the mouthfeel, flowability, and stability of emulsions
[3]. A variety of experimental techniques are available for measuring the rheological
properties of food emulsions. The rheology of emulsions that have low viscosities
and act like ideal liquids can be characterized by capillary viscometers. For nonideal
liquids or viscoelastic emulsions, more sophisticated instrumental techniques called
dynamic shear rheometers are available to measure the relationship between the stress
applied to an emulsion and the resulting strain, or vice versa. As well as providing
valuable information about the bulk physicochemical properties of emulsions (e.g.,
texture, flow through pipes), rheological measurements can provide information
about droplet–droplet interactions and the properties of any flocs formed in an
emulsion.
G. Interfacial Properties
Despite comprising only a small fraction of the total volume of an emulsion, the
interfacial region that separates the oil from the aqueous phase plays a major role in
determining stability, rheology, chemical reactivity, flavor release, and other overall
physicochemical properties of emulsions. The most important properties of the interface
are the concentration of emulsifier molecules present (the surface load), the
packing of the emulsifier molecules, and the thickness, viscoelasticity, electrical
charge, and (interfacial) tension of the interface.
A variety of experimental techniques are available for characterizing the properties
of oil–water interfaces (Table 2). The surface load is determined by measuring
the amount of emulsifier that adsorbs per unit area of oil–water interface. The thickness
of an interfacial membrane can be determined by light scattering, neutron scattering,
neutron reflection, surface force, and ellipsometry techniques. The rheological
properties of the interfacial membrane can be determined by means of the twodimensional
analog of normal rheological techniques. The electrical charge of the
droplets in an emulsion determines their susceptibility to aggregation. Experimental
techniques based on electrokinetic and electroacoustic techniques are available for
determining the charge on emulsion droplets. The dynamic or equilibrium interfacial
tension of an oil–water interface can be determined by means of a number of interfacial
tension meters, including the Wilhelmy plate, Du Nouy ring, maximum bubble
pressure, and pendant drop methods.
REFERENCES
1a. D. J. McClements. Food Emulsions: Principles, Practice and Techniques. CRC, Boca
Raton, FL, 1999.
1b. S. Friberg and K. Larsson. Food Emulsions. 3rd ed., Dekker, New York, 1997.
2. E. Dickinson and G. Stainsby. Colloids in Foods. Applied Science, London, 1982.
3. E. Dickinson. Introduction to Food Colloids. Oxford University Press, Oxford, 1992.
4. D. G. Dalgleish. Food emulsions. In: Emulsions and Emulsion Stability (J. Sjoblom,
ed.). Dekker, New York, 1996.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.