New views on foams from protein solutions

The stabilization of foam by proteins has been mostly studied in relation to the food industry. The main aim of the research is to understand the relation between proteins used and the product properties. The molecular properties of proteins and their foam forming and stabilizing properties are typically linked to the adsorption kinetics and the interfacial properties. Additionally, the properties of thin liquid films formed between neighboring air bubbles are considered. While there are several rules of thumb describing the relations between the different parameters and processes it seems that there is not yet a ‘unifying’ theory on protein stabilized foams. If the different processes could be described by quantitative parameters the applications of traditional proteins and the use of proteins from novel sources could be optimized. However, even for simple protein systems there is a lack of such quantitative rules, and as a result the advancement in the understanding of protein foam seems to progress slowly. This is attributed to the complexity of the system by some authors, but by viewing the literature it also becomes apparent that certain ideas seem to resist change. There are some interesting articles that offer a different point of view. In this article we aim to provide an insight in the different ways in which proteins and their role in foamed systems are described. Based on recent results, it seems that protein adsorption and subsequent changes in interfacial properties could be described in colloidal terms such as the net charge, exposed hydrophobicity and size of the proteins. Such a description can help to understand the behavior of single-component systems, but can also add to the understanding of the more complex systems that seem to attract more and more interest in recent years. An example of the value of using new viewpoints is the exchange of information between fields of food and non-food foams. Examples in this field are the use of particles to stabilize foams, or the production of very stable microbubbles.

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► Comparison of ‘loop-train’, or polymer description of adsorbed proteins with a colloidal description.
► Electrostatic and hydrophobic properties of proteins determine adsorption kinetics.
► Application of RSA model to describe protein adsorption.
► Role of aggregates and particles in (de-)stabilization of protein foams