Proteins as clean label ingredients in foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 203

Fig. 9.2 Schematic representation of the different degrees of structure in proteins for
different sources and the impact thereof on the required structuring to obtain the required
macroscopic properties. Copyright NIZO, 2012.

(charged) protein molecules at low ionic strength are required for the formation of
a fi brillar morphology. For example, the egg protein ovalbumin forms fi brils
ranging from 400-700 nm when heated at 72°C at pH 7.0 and low ionic strength,
3mM salt (Weijers et al. 2002, 2008). Unfortunately, the presence of other egg
proteins, such as ovomucoid, disturbs the fi bril formation (Weijers et al. 2006).
The reactivity of the thiol groups and disulfi de bridges (possibility to form cross-
links between protein molecules) is of key importance in this behavior. As a result
of this difference in reactivity whey proteins form banana-shaped aggregates with
a maximum length of around 100 nm when heated at a pH far away from the
isoelectric point and with no salt added (Alting et al. 2004). The difference in size
and shape between ovalbumin and whey protein aggregates is immediately
refl ected in the concentration dependency of the viscosity of protein aggregate
solutions (Fig. 9.3). The formation of disulfi de bonds during whey protein
aggregation can be diminished by lowering the pH of the solution. On heating
whey protein solutions, a low pH (2.0) and low ionic strength (0.01-0.08M)
fi brillar structures were formed with a size exceeding that of ovalbumin fi brils
(2-7 μm; Veerman et al. 2002).
The aggregation process described above results in protein molecules with a
higher viscosifying capacity compared with the native proteins. However, the
disadvantage is that this aggregation is carried out in dilute protein solutions.
Therefore, the concentration of the ingredient needs to be applicable on a large
scale in the food industry. Concentration can easily be achieved by membrane
fi ltration. The fi brillar structures can thus be prepared as a separate step in the

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