Bursting the bubble; How surfactants destabilize protein foams, revealed by atomic force microscopy

The bubbles in a pure protein foam are stabilized by elastic networks of pr otein molecules that adsorb to the air/water interface through hydrophobic interaction. In real systems, however, there are often other amphiphiles pr esent that have an antagonistic effect on the stability of the foam. This p aper describes the first direct observation of specific heterogeneous struc tures that occur during the competitive adsorption between proteins and sur factants, This is in contrast to the previous assumption of a homogeneous d istribution of the two competing species at the interface, By using atomic force microscopy to visualize the breakdown of protein networks, we have id entified the specific mechanism for surfactant displacement of proteins fro m an air/water interface. This mechanism, which we have termed an orogenic model of protein displacement, involves nucleation and growth of surfactant domains that compress and then fracture the protein network, eventually in ducing its displacement from the interface. Copyright (C) 1999 John Wiley & Sons, Ltd.