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The atomization of oil-in-water emulsions for spray-drying purposes is a common task in the food industry. In this process, atomization is used to create fine droplets from a liquid feed, which, by subsequent contact with a hot air stream, are dried into particles. By this means, powders with encapsulated oily components can be produced. The oil droplet size in the resulting powder is of upmost importance, as it affects the encapsulation efficiency, the physical stability of the product, as well as the sensorial properties of the reconstituted food. Pressure swirl nozzles are widely used in the food industry as atomization devices. Upon pressure swirl atomization the liquid feed is strongly accelerated in a narrow gap and subjected to intense shear and elongational stress. The stresses acting on the liquid feed can also lead to deformation and break-up of the dispersed oil droplets.
A break-up of oil droplets during atomization has already been reported in literature. However, only few studies have focused on this change of oil droplet size of emulsions upon atomization by means of pressure swirl nozzles. The present study focused on the pressure atomization of protein based oil-in-water emulsions to evaluate the influence of atomization conditions and formulation parameters on the oil droplet size after atomization. Model emulsions consisting of maltodextrin, whey protein isolate and MCT (medium chain tryglicerides) oil with different initial oil droplet size, emulsion viscosity and oil content were atomized at different pressures using commercial pressure swirl nozzles with varying inlet geometries. The experiments were carried out in an atomization test rig equipped with a laser diffraction spectroscope for online measurements of the spray droplet size. Samples of the spray were taken at the different atomization conditions and the oil droplet size distribution was analyzed offline by means of laser diffraction spectroscopy.
Oil droplet breakup was visible for almost all atomization conditions. The resulting oil droplet size distribution is highly dependent on the applied atomization pressure. Interestingly, the resulting oil droplet size seemed to be in a wide range independent of the obtained spray droplet size. Results of this study prove that by adjustment of process and formulation parameters, the oil droplet size after atomization can be controlled independently of the spray droplet size.
