The use of electro-hydrodynamic liquid systems (EHD) is one of the emerging technologies for coating foods with oils, emulsifiers or various flavorings. The fundamental operating principles of such systems are based on the fact that the surface area, and therefore liquids’ surface energy is constantly increased by the application of electrical forces up to the disintegration of the surface itself. At this point, the liquid is atomized and subsequently transformed into droplets with electrical charges that form the coating. Electrical resistivity and viscosity of fluids play a major role in determining the efficiency of EHD systems. In this context, in a recent survey, a group of American researchers (Marthina & Barringer, 2012), investigated the influence of these two characteristics in the case of different types of fats (i.e., cocoa butter, palm oil and a blend of sunflower oil and palm). The test has also investigated the influence of soy lecithin addition (between 0.05 and 5%). The results show that when the latter ingredient decreases, also the resistivity of all samples decreases. On the contrary, there is no clear correlation between the apparent viscosity of fats and the content of lecithin (at 0.5% content, viscosity decreases, at 1% it increases and at higher levels it decreases). The authors point out, moreover, that EHD system is able to form stable coatings even with less thickness than that provided by traditional methods. Thanks to the repulsive forces of the electrical charges, the droplets spread over larger surfaces than control samples. In conclusion, the authors point out that from an economic point of view these characteristics are crucial because they guarantee complete coverage of the same area, but with lower coating quantity.
K.Marthina & S.A. Barringer, Journal of Food Science, 71, 2012, E26-E31