Development of Dairy Water-in-Oil-in-Water Emulsions - Evaluation of surfactants and milk components as emulsifiers

Double emulsions have a great potential in food applications, such as low calorie products and to improve sensory properties. For the dairy industry, double emulsions could be used to produce a product with a lower fat content which maintain the same properties as regular whipping cream. The purpose of this project was to obtain a stable Water-in-Oil (W/O) emulsion with butter oil with a small mean droplet size which could be used to prepare a double emulsion. All the emulsions were prepared with a rotor - stator system. For the W/O emulsion studies, different surfactants such as polyglycerol polyricinoleate (PGPR), oat oil, and soy – and rapeseed - lecithin, were evaluated to see how different concentrations together with an addition of electrolytes and/or milk proteins, affected the mean droplet size and the creaming rate (emulsion stability). PGPR as a surfactant together with proteins, resulted in the smallest mean droplet size of 1.0 ± 0.1 µm, and the highest emulsion stability of 100 %. The emulsion stability was unaffected, independently of surfactant or milk proteins used as stabilizers, between 1 hour of storage and 48 hours of storage at 6°C. This shows that the crystalized fat in the butter contributes to the emulsion stability. W/O emulsions was also successfully prepared with oat oil and fluid rapeseed lecithin. However, the mean droplet size was larger, between 6.7 and 10.1 µm, compared to PGPR and the emulsion stability was around 90 %. W/O/W (10/90) emulsions were successfully prepared with a W/O (20/80) emulsion containing 2 wt % PGPR and 2 wt% MPC. The smallest mean droplet size of 8.6 ± 0.5 µm was obtained with SMP in the external aqueous phase. By varying the aqueous phase from 20 wt% to 30 wt% in the inner emulsion, the mean droplet size went from 1 µm to 2 µm. Also, a W/O/W emulsion, containing an inner emulsion of 20 and 30 wt% aqueous phase, respectively, showed a significantly increase in mean droplet size from 13.6 ± 0.6 to 15.0 ± 0.7 µm (P<0.01). The emulsion stability of all the W/O/W emulsions was poor, and through microscopic examination, big and coalesced W/O/W emulsion droplets could be distinguish. A suggestion for this appearance could either be caused by the rather large mean droplet size, partial aggregation and/or the osmotic pressure, where the water migrates to the inner aqueous phase causing the emulsion droplet to swell. Further investigations have to be done to enhance the stability of double emulsions. By suggestion, it could be done by alter the protein concentration for the second emulsification, alternatively add another type of emulsifier, as well as controlling the temperature.