- Unique Emulsions based on recombinant Hydrophobins (2012)
- Hydrophobins are very interesting proteins of fungal origin. Beside their relatively small size of around 100 amino acids, they are well known to be the most surface active, natural proteins that have a strong tendency for self-assembly. Due to their versatile properties hydrophobins are present in different fungal structures, like as coaters of hyphae. These diversified properties of hydrophobins raised great interest among scientists. Possible applications in surface modification or emulsion industry were always restricted by the cost and effort of natural hydrophobin purification. This changed dramatically by the use of white biotechnology resulting in the availability of high amounts of recombinant hydrophobins nowadays. This study started with the physicochemical characterization of two recombinant hydrophobins, called H Star Proteins ® A and B. Both show a remarkable, time-dependent surface activity as well as a distinct aggregation behaviour indicating them to have the typical properties of natural hydrophobins. The use of the recombinant hydrophobins as emulsifier resulted in the formation of gel-like oil in water emulsions. Interestingly, without the occurrence of typical emulsion instability processes like creaming or coalescence, these emulsions showed significant aging effects. We conclude them to be the consequence of the time-dependent formation and progression of a self-supporting, three-dimensional protein network that evolves in the emulsion. The self-assemble tendency of recombinant hydrophobins is clearly not limited by adsorption to the oil-water interface. Obviously the long term stability of the emulsion is determined by the sticky character of the hydrophobin coated oil droplets that attract each other in the short range distance. This type of emulsion stabilization mechanism is absolutely novel in the field of emulsion technology. Moreover we used the hydrophobins’ ability of surface modification in order to coat disk-like clay particles. These clay-hydrophobin sandwiches were used for the formation of Pickering Emulsions. It turned out that the synergistic use of clay and hydrophobin resulted in homogenous, long-term stable and tooth-paste like emulsions. The clay particles improved strikingly the rigidity and elasticity of the self-supporting hydrophobin network. Substitution of the clay particles by boehmite needles resulted in similar Pickering emulsions. Finally, we report that it is possible to replace hydrophobin in combination with clay by other proteins, amphiphiles or surfactants. By adjusting the preparation conditions, the emulsifier concentration or the oil mass fraction one has a versatile tool to obtain Pickering emulsions with the desired properties. A new stabilization mechanism in emulsion science is introduced, supported and confirmed by our results.