How can the protein lactalbumin reduce the surface tension of water and work like an emulsifying agent in milk?
I dont know why lactalbumin reduces the surface tension but If you know the concepts of surface tension and surfactants then it becomes easier to extrapolate on that concepts to reach the conclusion why lactalbumin reduces surface tension?
According to HyperPhysics surface tension is the
The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface "film" which makes it more difficult to move an object through the surface than to move it when it is completely submersed.
And the choesive force is caused by the hydrogen bonds due to the strong interactions between water molecules
And according to wikipedia
Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid.
This image shows how a surfact decreases the surface tension of a liquid by causing interference in the hydrogen bonds between water molecules
Similarly lactalbumin which has a core hydrophobic group and other functional group such as thiol(Beta lactalbumin) which may interfere in water-water hydrogen bond causing decrease in surface tension.