Fat-free mayonnaise thanks to manipulation of surface tension
Aqueous solutions of proteins and carbohydrates separate into two parts with an extremely ‘soft’ boundary surface. The surface tension between these two parts can be manipulated, for example by adjusting the pH balance. This can be used to develop emulsions of a water-based solution in another aqueous solution, such as fat-free mayonnaise. Leiden researchers were involved in the investigation. Physical Review Letters, 6 August 2015.
The theoretical foundation for this research was provided by Leiden researchers from the Colloid and Interface Science (CIS) research group of the Leiden Institute of Chemistry. Edgar Blokhuis explains: 'Both parts of the emulsion consist of 90% water. As a result, small molecules such as ions have no trouble moving through the water-water boundary. Thanks to their electric charge, the ions are attracted to protein molecules and will therefore primarily move towards the protein part, which is not ideal from a statistical perspective. In collaboration with the researchers responsible for the practical implementation we developed a theory to map this conflict. This theory leads to a surprisingly simple formula for reducing the surface tension that also happens to precisely match the experimental results.’
This research was initiated by researchers from Utrecht University and NIZO Food Research. Mark Vis, PhD candidate at Utrecht University and first author of the publication, conducted very precise experiments with mixtures of proteins and carbohydrates in 90% water. Since the proteins and the carbohydrates try not to mix a boundary forms with a surface tension that is up to one million times lower than that between oil and water. The researchers managed to further manipulate the surface tension by adjusting the pH balance, which impacts the electric charge of the protein, causing a difference in electrical tension between the two parts. The researchers established the precise effect of this difference on the surface tension.
Left: A carbohydrate and protein solution has spontaneously separated into two phases, one of which is rich carbohydrates and the other in protein.
Middle: The surface tension is determined by the shape of the water-water boundary near a wall.
Right: Schematic representation of the water-water surface, with carbohydrates in blue and proteins in red.
Mixtures of proteins and carbohydrates are relevant for applications in the food industry. Controlling the surface tension is an important step in manipulating the tendency of these mixtures to separate. Proteins and carbohydrates appear in many food products, but it is not the intention that they separate in these products. In some cases, however, a strong separation may actually be desirable, for example to develop mayonnaise that does not consist of droplets of oil in water, but rather droplets of water in water. Many studies of these kinds of systems are purely empirical: researchers try out different things to see what works. This study provides a theoretical framework that makes it possible to specifically define the circumstances required to create the desired emulsion.