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Atomic force microscopy (AFM) is still a relatively new form of microscopy. Unlike conventional microscopes the AFM generates images by feeling the surface of the sample: the microscope senses the changes in force between the surface and a probe as the sample is scanned relative to the probe. An analogy is a blind person who produces images by touch. Much as the blind person can generate images of surface shape, hardness and stickiness, so the AFM can produce images of surface topography, adhesion, elasticity or charge. This mini review will be concerned solely with topographical imaging and its application to study food biopolymers. Current commercial AFMs permit submolecular resolution under gaseous or liquid environments and, under suitable circumstances, it is possible to image molecular processes in real time. This article is intended as a mini review of applications of AFM in food science which permit a molecular understanding of the rheology of food biopolymers.

The bubbles in a pure protein foam are stabilized by elastic networks of protein molecules that adsorb to the air/water interface through hydrophobic interaction. In real systems, however, there are often other amphiphiles present that have an antagonistic effect on the stability of the foam. This paper describes the first direct observation of specific heterogeneous structures that occur during the competitive adsorption between proteins and surfactants. This is in contrast to the previous assumption of a homogeneous distribution of the two competing species at the interface. By using atomic force microscopy to visualize the breakdown of protein networks, we have identified the specific mechanism for surfactant displacement of proteins from 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 inducing its displacement from the interface. Copyright © 1999 John Wiley & Sons, Ltd.