Chemistry Reference
In-Depth Information
way as the oil droplet it replaces and is then connected to the structure
with the same strength of bonding and thermal liability.
We will now illustrate the approach by considering a number of
successful applications:
10.3.1
Use of emulsions as partial fat replacement
The first approach is to replace pure fat with an emulsion. By doing this,
the calorific value of the food will be reduced. Here, there is a whole new
area of rheology that needs to be considered: interfacial rheology. This
can be a consequence of low molecular weight surfactants assembling
at an interface, thus imparting a change in interfacial rheology or it can
be where large molecular weight material is adsorbed or where there is
low molecular weight material aggregate due to the increased concentra-
tion. These then lead to a surface modulus or even a gel-like structure.
This imparts a surface elasticity, which needs to be considered when
designing our healthy everyday foods. If this is to be used in a practical
sense, a rheological issue is raised, which needs to be considered; in
terms of the measurement and control of interfacial rheology, and in
practical terms, how does the practitioner/product developer measure
this physical property accurately and reliably? This question will need
to be addressed in the future.
One step further is to use particles at the interface (Pickering stabili-
sation). One way to use these is to construct emulsions which allow the
addition of water to products where it is generally considered to be im-
possible because it causes dramatic changes in the material properties,
often as a result of the solubility of sugar in water, for example chocolate.
So if this is to be done, a totally new way of thinking about structures
is required. Recent work (Norton
et al
., 2009) has approached this by
moving into the area of Pickering stabilisation of emulsions. However,
a simple Pickering emulsion would not work, as the water would be free
to move out of the droplets to solubilise the sugar. What the authors did
in order to try and overcome this effect was to place crystals at the inter-
face to build an intact shell (Fig. 10.8), thus offering protection against
water movement. The figure shows an electron microscope picture of the
cocoa butter emulsion. The shell of fat crystals around the water droplet
can clearly be seen. It appears as if the crystals have sintered together
and the structure appears to be fairly smooth. Of course, this requires the
production of a crystalline shell with no defects. More recent work has
been carried out with gelling of the aqueous phase to address this issue.
This would give further strength to the structure, but the advantage of
gelatin is that it melts at the same temperature as the fat phase, thus
anything obtained in the droplets will be released on consumption. No
doubt more revelations will emerge from this group in the future.
