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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Table 2 Experimental Techniques for Characterizing the Physicochemical Properties of<br />

<strong>Food</strong> Emulsions [1a]<br />

Dispersed phase volume Proximate analysis, density, electrical conductivity, light<br />

fraction<br />

scattering, NMR, ultrasound<br />

Droplet size distribution Light scattering (static <strong>and</strong> dynamic), electrical<br />

conductivity, optical microscopy, electron<br />

microscopy, ultrasound, NMR<br />

Microstructure Optical microscopy, electron microscopy, atomic force<br />

microscopy<br />

Creaming <strong>and</strong> sedimentation Light scattering, ultrasound, NMR, visual observation<br />

Droplet charge Electrokinetic techniques, electroacoustic techniques<br />

Droplet cyrstallization Density, NMR, ultrasound, differential scanning<br />

calorimetry, polarized optical microscopy<br />

Emulsion rheology Viscometers, dynamic shear rheometers<br />

Interfacial tension Interfacial tensiometers (static <strong>and</strong> dynamic)<br />

Interfacial thickness Ellipsometry, neutron reflection, neutron scattering, light<br />

scattering, surface force apparatus<br />

volume fraction of emulsions are outlined in Table 2. Traditional proximate analysis<br />

techniques, such as solvent extraction to determine oil content <strong>and</strong> oven drying to<br />

determine moisture content, can be used to analyze the dispersed phase volume<br />

fraction of emulsions. Nevertheless, proximate analysis techniques are often destructive<br />

<strong>and</strong> quite time-consuming to carry out, <strong>and</strong> are therefore unsuitable for rapid<br />

quality control or on-line measurements. If the densities of the separate oil <strong>and</strong><br />

aqueous phases are known, the dispersed phase volume fraction of an emulsion can<br />

simply be determined from a measurement of its density:<br />

� =(� � � )(� � � ) (15)<br />

emulsion continuous phase droplet continuous phase<br />

The electrical conductivity of an emulsion decreases as the concentration of oil<br />

within it increases, <strong>and</strong> so instruments based on electrical conductivity can also be<br />

used to determine �. Light scattering techniques can be used to measure the dispersed<br />

phase volume fraction of dilute emulsions (� < 0.001), whereas NMR <strong>and</strong> ultrasound<br />

spectroscopy can be used to rapidly <strong>and</strong> nondestructively determine � of concentrated<br />

<strong>and</strong> optically opaque emulsions. A number of these experimental techniques<br />

(e.g., ultrasound, NMR, electrical conductivity, density measurements) are particularly<br />

suitable for on-line determination of the composition of food emulsions during<br />

processing.<br />

B. Droplet Size Distribution<br />

The size of the droplets in an emulsion influences many of their sensory <strong>and</strong> bulk<br />

physicochemical properties, including rheology, appearance, mouthfeel, <strong>and</strong> stability<br />

[3,5]. It is therefore important for food manufacturers to carefully control the size<br />

of the droplets in a food product <strong>and</strong> to have analytical techniques to measure droplet<br />

size. Typically, the droplets in a food emulsion are somewhere in the size range of<br />

0.1–50 �m in diameter.<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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