Food Lipids: Chemistry, Nutrition, and Biotechnology

extensive nonpolar groups (e.g., caseins, denatured whey proteins) tend to associate
via hydrophobic interactions. Electrostatic interactions play an important role in determining
the gelation behavior of many biopolymers, and so gelation is particularly
sensitive to the pH and ionic strength of the solution containing the biopolymers.
For example, at pH values sufficiently far from their isoelectric point, proteins may
be prevented from gelling because of the electrostatic repulsion between the molecules.
However, if the pH of the same solution is adjusted near to the isoelectric
point, or salt is added, the proteins gel.
The addition of multivalent ions, such as Ca 2� , can promote gelation of charged
biopolymer molecules by forming salt bridges between the molecules. Proteins with
thiol groups are capable of forming covalent linkages through thiol–disulfide interchanges,
which help to strengthen and enhance the stability of gels. The tendency
for a biopolymer to form a gel under certain conditions, and the physical properties
of the gel formed, depend on a delicate balance of biopolymer–biopolymer, biopolymer–solvent,
and solvent–solvent interactions of various kinds.
C. Ingredient Selection
A wide variety of proteins and polysaccharides are available as ingredients in foods,
each with its own unique functional properties and optimum range of applications.
Food manufacturers must decide which biopolymer is the most suitable for each type
of food product. The selection of the most appropriate ingredient is often the key to
success of a particular product. The factors a manufacturer must consider include
the desired properties of the final product (appearance, rheology, mouthfeel, stability),
the composition of the product, and the processing, storage, and handling conditions
the food will experience during its lifetime, as well as the cost, availability,
consistency from batch to batch, ease of handling, dispersibility, and functional properties
of the biopolymer ingredient.
V. EMULSION FORMATION
The formation of an emulsion may involve a single step or a number of consecutive
steps, depending on the nature of the starting material, the desired properties of the
end product, and the instrument used to create it [1a]. Before separate oil and aqueous
phases are converted to an emulsion, it is usually necessary to disperse the various
ingredients into the phase in which they are most soluble. Oil-soluble ingredients,
such as certain vitamins, coloring agents, antioxidants, and surfactants, are mixed
with the oil, while water-soluble ingredients, such as proteins, polysaccharides, sugars,
salts, and some vitamins, coloring agents, antioxidants, and surfactants, are
mixed with the water. The intensity and duration of the mixing process depends on
the time required to solvate and uniformly distribute the ingredients. Adequate solvation
is important for the functionality of a number of food components. If the lipid
phase contains any crystalline material, it is usually necessary to warm it before
homogenization to a temperature at which all the fat melts; otherwise it is difficult,
if not impossible, to efficiently create a stable emulsion.
The process of converting two immiscible liquids to an emulsion is known as
homogenization, and a mechanical device designed to carry out this process is called
a homogenizer. To distinguish the nature of the starting material, it is convenient to
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