b-Lactoglobulin Aggregates from Heating with Charged Cosolutes: Formation, Characterization and Foaming - Food Colloids: Self-Assembly and Material Science - page 192

12.4 Conclusions
This study has demonstrated that the use of soluble and/or insoluble aggregates
formed during heat treatment of b-LG in the presence of cosolutes increases the
foam stability parameters significantly. The presence of charged cosolutes
initiates electrostatic charge screening, leading to protein aggregation during
heat treatment, and also to reduced repulsive forces of the proteins on
adsorption at the air water interface. It has been further demonstrated that
the nature of the cosolute has no direct effect on foam stabilization, but only on
the extent of formation of soluble and insoluble aggregates. As a result the
foam volume stability was increased, the foam drainage was reduced (control-
led by interfacial viscoelasticity) and the rate of bubble disproportionation
considerably lowered. This was explained by the formation of stable interfacial
networks, comparable with gel-like networks entrapping the air bubbles.
Owing to low repulsive forces between the proteins adsorbed at the air-water
interface, the interfacial films are stabilized by increased intermolecular cross-
linking, hydrophobic and electrostatic interactions between the proteins/parti-
cles. Interfacial elasticity and viscosity were found to reach maximum values
under conditions prior to aggregate precipitation (C cs ).
The presence of insoluble aggregates (1-10 mm) has been found significant to
improve foam stability, presumably through contributions to disjoining pres-
sure forces from steric and electrostatic repulsion. The presence of large
amounts of soluble aggregates (480%), and the incorporation of insoluble
protein aggregates in a stable interfacial network, thereby entrapping the air
bubbles, was found to reduce foam coarsening significantly. However, when
aggregation was too strong, foam destabilization occurred due to film rupture,
presumably induced by bridging of the thin films by the particles. The forma-
tion of a stable gas diffusion barrier against disproportionation and film
rupture depends, therefore, not only on the presence of soluble and insoluble
protein aggregates with specific sizes and molecular characteristics, but also on
the ability to cross-link at the interface via electrostatic, hydrophobic and
covalent SH-SS exchange.
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