Adsorption of Macromolecules at Oil
Water Interfaces during Emulsification - Food Colloids: Self-Assembly and Material Science - page 441

Figure 7 SDS PAGE of soluble egg yolk proteins at protein concentration c 0 ¼ 1mg
mL 1 . 12 (a) The bands refer to samples before emulsification (U) and after
emulsification at varying pH values (numbers from 2.8 to 8). (b) The inte-
grated lane profiles are labelled as in Figure 1

30.4 Discussion
Having observed contrasting examples of selective adsorption for two different
kinds of macromolecules, we now consider the possible reasons for this selec-
tivity. The adsorption can be described as being controlled by kinetics, affinity,
or equilibrium considerations. In what follows, we discuss these mechanisms
and their influence on the results obtained in this study.

30.4.1 Kinetically Controlled Adsorption
The experiments for OSA-starch gave very high surface loads. In a high-
pressure homogenizer the adsorption occurs under turbulent flow conditions,
and the transport to the interface is dominated by convection rather than by
diffusion, which would be the case under quiescent conditions. Owing to the
convective mass transport, larger molecules are transported more rapidly to the
interface, which is the opposite to what applies for diffusional mass transport.
The adsorption process can be described as a collision between particles in
turbulent flow. By invoking the theory of isotropic turbulence, and assuming
that the particles are not smaller than the turbulence microscale, known as the
Kolmogorov scale, the collision frequency can be represented by 29,30

7 = 3 e 1 = 3 n p n d ;

N ¼ 1 : 4 p r p þ r d ð 1 Þ

where r p and r d are the radii of the polymer and the emulsion droplets, and
n p and n d are the number concentrations of these species. We can express the