Chemistry Reference
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properties to air-filled droplets as those observed for hydrophobins (Cox
et al.
, in press).
Having produced air-filled emulsions, which is one step on the road to
using them in foods, it is also necessary for complex food formulations
to have the stability in the presence of oil droplets. Oil is an antifoam in
aerated products as it normally adds a level of mobility to the air/water
interface. This allows the surfactants to move and cause film drainage,
allowing the air to escape within a few minutes or hours. However, as
fat is a carrier of flavour in many products, there will be a need to have
some oil present. This means that we will have to construct a triphasic
system. So, again, can rheological understanding and control give us a
route to overcome this obstacle?
As discussed earlier, the initial work was performed using hydro-
phobin proteins and alternatives have been developed. The reason for
developing alternatives was two-fold. The first was that hydrophobins
are currently scarce and expensive. The second reason is that the kinetics
of structuring at the interface is hard to control, and once the proteins
are aggregated at the interface, any further application of shear in the
process causes the proteins to detach from the interface and become
inactive. The alternatives are food grade proteins that are thermally
denaturing at the interface using sonication, which produces small air
cells at the same time (Fig. 10.12). The proteins, which are applicable,
are high in cysteine residues so that they covalently cross-link to form
an elastic robust interface. It has been shown (de Vocht, 2001) that the
kinetics of ordering and the point at which cross-linking occurs within
the process can more easily be controlled than for the hydrophobins.
Fig. 10.12
A light photomicrograph of a BSA-stabilised air-filled emulsion. This sample
is 140 days old and showed almost no Ostwald ripening over this time.
