Unique emulsions based on biotechnically produced hydrophobins

Abstract

The emphasis of this manuscript is on emulsions with gel-like properties based on biotechnically produced hydrophobins. These emulsions are compared to emulsions based on surfactants. Even though the preparation conditions for both emulsion types were the same, the structure and the properties were very different. Homogeneous, gel-like emulsions could be obtained with a protein concentration between 0.02 and 1 wt% and an oil mass fraction of more than 0.65. The gelified state is formed because the protein-covered droplets behave like sticky spheres even when the globules are ionically charged and the long range interaction is repulsive. Conductivity and microscopy measurements showed that the emulsions were of the oil in water (o/w) type. The size of the emulsion droplets depends on the mixing apparatus. With a vortex shaker oil droplets of up to 100 μm diameter were obtained indicating some protein remained in the bulk aqueous phase. With a high pressure homogenizer the emulsion droplets got much smaller and the protein was completely adsorbed at the droplet interface. Interestingly the emulsions aged with time without changing their structure. The aging was a result of the increase of the storage modulus G′. In the case of surfactants no homogeneous stable emulsions could be obtained under the same conditions.