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Watery solutions of proteins and carbohydrates separate into two parts with an extremely ‘soft’ boundary surface. It is possible to manipulate the surface tension between these two parts. This can be useful in the development of emulsions of a water-based solution in another watery solution, such as fat-free mayonnaise. That is the conclusion of a team of researchers from Utrecht ľ�ϸ���Ӱ��, ľ�ϸ���Ӱ�� of Leiden and NIZO food research. They published the results of their study in the prestigious journal Physical Review Letters on 6 August.

The researchers conducted experiments with mixtures of proteins and carbohydrates in 90% water. As with mixtures of oil and water, this fluid separated into two parts. “The proteins and the carbohydrates don’t want to mix together, so a boundary forms between the two layers,” according to Mark Vis, PhD Candidate at Utrecht ľ�ϸ���Ӱ�� and first author of the publication. “The surface tension, however, is up to one million times lower than that between oil and water.”

Electrical charge

The researchers managed to manipulate the surface tension between the protein-rich and carbohydrate-rich layers of the mixture by adjusting the PH balance. The PH balance has an effect on the electric charge of the protein. “We studied which effect the electric charge of the protein has on the surface tension,” explains Mark Vis. “We observed that the protein’s electric charge dissolved the boundary between the two parts of the fluid.”

Fat-free mayonnaise

Mixtures of proteins and carbohydrates are relevant for applications in the food processing industry. Controlling the surface tension is an important step in manipulating the tendency of these mixtures to separate. Proteins and carbohydrates are ingredients in many food products, but it is not the intention that they separate in these products. But in other cases, a strong separation is actually desirable, for example to develop mayonnaise that does not consist of droplets of oil in water, but rather of droplets of water in water.

Theoretical foundation

Since both parts consist of 90% water, tiny molecules such as ions have no trouble moving through the water-water barrier. This gives the barrier a number of unique characteristics. The researchers were able to explain their experimental results with a theoretical foundation. “Many studies of these kinds of systems are purely empirical: the scientists try out different things and see what works. Our research gives it a solid theoretical context,” says Mark Vis.

Mark Vis is one of the authors of . He will be defending his thesis titled Interfacial Thermodynamics of Coexisting Aqueous Polymer Solutions on Monday, 23 November in ľ�ϸ���Ӱ�� Hall in Utrecht.