Food Lipids: Chemistry, Nutrition, and Biotechnology

alteration in the system’s composition or environmental conditions, such as dispersed
phase volume fraction, emulsifier type, emulsifier concentration, temperature, or application
of mechanical forces. Phase inversion is believed to occur by means of a
complex mechanism that involves a combination of the processes that occur during
flocculation, coalescence, and emulsion formation. At the point where phase inversion
occurs, the system may briefly contain regions of oil-in-water emulsion, waterin-oil
emulsion, multiple emulsions, and bicontinuous phases, before converting to
its final state.
6. Chemical and Biochemical Stability
Chemical and biochemical reactions of various types (e.g., oxidation, reduction, or
hydrolysis of lipids, polysaccharides, and proteins) can cause detrimental changes in
the quality of food emulsions. Many of these reactions are catalyzed by specific
enzymes that may be present in the food. The reactions that are important in a given
food emulsion depend on the concentration, type, and distribution of ingredients, and
the thermal and shear history of the food. Chemical and biochemical reactions can
alter the stability, texture, flavor, odor, color, and toxicity of food emulsions. Thus
it is important to identify the most critical reactions that occur in each type of food
so that they can be controlled in a systematic fashion.
VII. CHARACTERIZATION OF EMULSION PROPERTIES
Ultimately, food manufacturers want to produce a high quality product at the lowest
possible cost. To achieve this goal they must have a good appreciation of the factors
that determine the properties of the final product. This knowledge, in turn, is used
to formulate and manufacture a product with the desired characteristics (e.g., appearance,
texture, mouthfeel, taste, shelf life). These bulk physicochemical and sensory
properties are determined by such molecular and colloidal properties of emulsions
as dispersed volume fraction, droplet size distribution, droplet–droplet
interactions, and interfacial properties. Consequently, a wide variety of experimental
techniques have been developed to characterize the molecular, colloidal, microscopic,
and macroscopic properties of food emulsions [1a]. Analytical techniques are needed
to characterize the properties of food emulsions in the laboratory, where they are
used to improve our understanding of the factors that determine emulsion properties,
and in the factory, where they are used to monitor the properties of foods during
processing to ensure that the manufacturing process is operating in an appropriate
manner. The subsections that follow highlight some of the most important properties
of food emulsions and outline experimental techniques for their measurement.
A. Dispersed Phase Volume Fraction
The dispersed phase volume fraction or � is the volume of emulsion droplets (VD) divided by the total volume of the emulsion (VE): � = VD/VE. The dispersed phase
volume fraction determines the relative proportion of oil and water in a product, as
well as influencing many of the bulk physicochemical and sensory properties of
emulsions, such as appearance, rheology, taste, and stability. For example, an emulsion
tends to become more turbid and to have a higher viscosity when the concentration
of droplets is increased [1a]. Methods for measuring the dispersed phase
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