variable oil–water ratio, this way of plotting leads to consistent results
(plotting as in Figure 11.15a does not). Results for some other proteins are
also given, and the differences cannot be easily explained. It may be noted
that during formation of emulsions and foams by agitation, the interface is
repeatedly expanded and compressed. This will induce conformational
changes (‘‘denaturation’’) in the adsorbed molecules, some of which changes
will be irreversible or very sluggishly reversible. Some molecules will become
desorbed and may readsorb in a changed form. Ovalbumin—and other
proteins showing a similar relation forG—become more or less aggregated
during emulsification, especially at high concentration.
Question 1
An emulsion is made of 100 mL triglyceride oil and 400 mL of a 20 millimolar NaCl
solution. 15 g of lauric acid (C12) is dissolved in the oil. The mixture is homogenized
FIGURE11.15 Surface excess (G) of proteins at the O–W interface as a function of
protein concentration. (a) Results forb-casein obtained by quiescent adsorption
onto a plane interface or by emulsification; cB is concentration in the bulk
(continuous) phase. (b) Results obtained by emulsification for various proteins;cTis
total concentration in the system, andA is the interfacial area produced by
emulsification. The broken line would be obtained if all of the protein became
adsorbed.