Instant Emulsions - Food Colloids: Self-Assembly and Material Science - page 414

manual - operation, thereby allowing the spreadable emulsion to be prepared
within a few minutes. The final emulsion should be easy to make and stabilize,
and with the potential for generating curiosity and interest in a consumer who
has the personal ability to create and observe the change in sensory properties.
Contrary to the well-established preparation of products such as soups or
dressings from instant powders, the final product described here is not simply
obtained by dilution or dissolution of dry material. Nevertheless, starting from
a base composition, a stable emulsion structure of high-quality can be obtained
with minimal energy input.
Emulsions are commonly employed in food, pharmaceutical and cosmetic
industries, where they have the ability to deliver both lipophilic and hydrophilic
ingredients in a kinetically stable product. Research in emulsion science and
technology has provided understanding about how to manipulate composition,
microstructure, (in)stability and texture. Nonetheless, much of the effort in the
past has focused on how emulsions can be most efficiently produced, with
considerable work done on optimizing emulsion droplet-size distributions
through homogenizer head design, membrane emulsification techniques,
sonication and so on.
To overcome the need to transport water, and to offer consumers lower-cost
alternatives, a range of dried food products has been developed. Improved
hydration of powders through agglomeration has led to increased quality of dry
food preparations. Additionally, emulsions that can easily be rehydrated, such
as powdered toppings, are widely available; these are based upon spray-dried
crystallized fat-containing emulsions. Nonetheless, such systems allow little or
no control over final emulsion properties, and the spray drying can have a
negative impact on the quality of the product, while still requiring sophisticated
processing prior to distribution.
The formulation of instant emulsions offers some particularly interesting
technical challenges. Interfacial stabilization of oil-in-water (O/W) emulsions is
typically provided by milk proteins, but only once the protein has been fully
rehydrated. Potentially this may limit the functionality of the protein when
used in an instant emulsion. This may be overcome if alternative low-
molecular-weight emulsifiers can be used which are delivered from the oil
phase. When both types of surface-active ingredients are combined in a mixture
of proteins and low-molecular-weight emulsifiers, an understanding of the
relative hydration kinetics and surface activity becomes mandatory.
Food emulsions are also structured and stabilized by rheological manipula-
tion of the continuous phase using thickening and/or gelling agents. These are
typically hydrated in factory processes, using heat and shear. This is particu-
larly relevant in the case of low-fat emulsions, which increasingly rely upon the
structuring of the aqueous phase to provide the required rheological attributes,
e.g., low-fat mayonnaise (containing starch) and low-fat spreads (containing
gelatin). Hydration rates of thickening and gelling ingredients will also have an
effect on the bulk structuring of the aqueous phase of instant emulsions.
Furthermore, the competitive hydration of hydrocolloids and surface-active
materials may also affect the ability to texturize and stabilize emulsions.