Chemistry Reference
In-Depth Information
Chapter 24
Enhancement of Stability of Bubbles to
Disproportionation Using Hydrophilic Silica
Particles Mixed with Surfactants or
Proteins
Thomas Kostakis, Rammile Ettelaie and Brent S. Murray
PROCTER DEPARTMENT OF FOOD SCIENCE, UNIVERSITY OF
LEEDS, LEEDS LS2 9JT, UK
24.1 Introduction
Incorporation of air bubbles into many food products (fizzy drinks, beer, ice-
cream, whipped cream, etc.) is an essential aspect of the process by which the
desired texture and rheology in these systems are developed. From a thermo-
dynamic point of view, these systems are very unstable and thus it is always a
challenge to the food technologist to find the best way to enhance the stability
of the bubbles. In the absence of coalescence, the major factor limiting the
bubble lifetime is the phenomenon of disproportionation, whereby gas diffuses
from smaller bubbles to larger ones as a consequence of differences in the
Laplace pressure between bubbles of different sizes.
Recent work has shown
1
that the interfacial elasticity of a wide range of
commonly used food proteins is insufficient to slow disproportionation signif-
icantly, so that bubbles below
100 mm diameter dissolve in less than a few
hours. On the other hand, it was also found
2
that partially hydrophobic,
spherical silica particles (made hydrophobic by chemical grafting of the correct
proportion of alkyl chains to their surface) can stabilize bubbles against
disproportionation for several days or even months.
One of the key parameters influencing the stabilization of emulsions and
foams by solid particles is the size of these particles. There have been many
studies in the past where the importance of particle size has been explored in
detail. Tang and co-workers
3
examined a wide range of spherical monodisperse
hydrophobic silica particles (20-700 nm in diameter). They reported
3
that foam
stability decreased with increasing particle size and increased with increasing
particle concentration, but without explaining the exact role that the particles
B
357
Search WWH ::
Custom Search