EFFECT OF CONTAMINANT ON ADSORPTION OF WHEY PROTEINS AT THE AIR-WATER-INTERFACE

The dynamics of adsorption of commercial samples of alpha-lactalbumin and beta-lactoglobulin was investigated through the measurement of dyn amic surface pressure and surface concentration via a radiotracer meth od. An unusual two-step adsorption behavior was observed for both prot eins at low concentration which was believed to be due to the presence of a surface active contaminant. This hypothesis was tested by compar ing the native whey protein samples with those purified with charcoal extraction. Analysis of the charcoal extract by thin-layer chromatogra phy revealed the presence of contaminating free fatty acid and triglyc erides in the commercial samples. beta-Lactoglobulin was found to cont ain a higher concentration of these contaminants than alpha-lactalbumi n. Extraction by charcoal was found not to modify the protein structur e with respect to their near- and far-UV circular dichroism spectra. T he presence of contaminant resulted in a higher steady-state surface p ressure for beta-lactoglobulin, but the protein was not displaced from the interface. On the other hand, the presence of a low concentration of surfactant was sufficient to decrease the steady-state surface con centration of alpha-lactalbumin due to the displacement of the protein from the interface by the lipids.