Abstract
Proteins are mostly used to stabilize food emulsions; however, production of protein containing emulsions is notoriously difficult to capture in scaling relations due to the complex behavior of proteins in interfaces, in combination with the dynamic nature of the emulsification process. Here, we investigate premix membrane emulsification and use the Ohnesorge number to derive a scaling relation for emulsions prepared with whey protein, bovine serum albumin (BSA), and a standard emulsifier Tween 20, at various concentrations (0.1%, 0.5%, 1.25% and 2%). In the Ohnesorge number, viscous, inertia, and interfacial tension forces are captured, and most of the parameters can be measured with great accuracy, with the exception of the interfacial tension. We used microfluidic Y-junctions to estimate the apparent interfacial tension at throughputs comparable to those in premix emulsification, and found a unifying relation. We next used this relation to plot the Ohnesorge number versus P-ratio defined as the applied pressure over the Laplace pressure of the premix droplet. The measured values all showed a decreasing Ohnesorge number at increasing P-ratio; the differences between regular surfactants and proteins being systematic. The surfactants were more efficient in droplet size reduction, and it is expected that the differences were caused by the complex behavior of proteins in the interface (visco-elastic film formation). The differences between BSA and whey protein were relatively small, and their behavior coincided with that of low Tween concentration (0.1%), which deviated from the behavior at higher concentrations.
Highlights
Many food emulsions are prepared by standard homogenization techniques such as high-pressure homogenizers, colloid mills, or rotor stator systems, and the stabilizers of choice are proteins.Microstructured systems used for the production of emulsions are claimed to have lower energy requirements and higher control over the droplet size distribution than conventional equipment [1,2,3,4], and are interesting alternatives for more traditional techniques that are much higher in energy demand.Membranes can be used in two operation modes: direct membrane emulsification and premix membrane emulsification
The results wereobtained obtained for premix membrane emulsification can be summarized a
The results thatthat were for premix membrane emulsification can beusing summarized modified Ohnesorge number, which accounts for viscous, inertia, and interfacial forces, and a using a modified Ohnesorge number, which accounts for viscous, inertia, and interfacial forces, pressure ratio that relates the applied pressure and the Laplace pressure of the droplet
Summary
Many food emulsions are prepared by standard homogenization techniques such as high-pressure homogenizers, colloid mills, or rotor stator systems, and the stabilizers of choice are proteins.Microstructured systems (membranes, microsieves or microfluidic devices) used for the production of emulsions are claimed to have lower energy requirements and higher control over the droplet size distribution than conventional equipment [1,2,3,4], and are interesting alternatives for more traditional techniques that are much higher in energy demand.Membranes can be used in two operation modes: direct membrane emulsification (cross-flow membrane emulsification) and premix membrane emulsification. Microstructured systems (membranes, microsieves or microfluidic devices) used for the production of emulsions are claimed to have lower energy requirements and higher control over the droplet size distribution than conventional equipment [1,2,3,4], and are interesting alternatives for more traditional techniques that are much higher in energy demand. The to-be-dispersed phase flows through the membrane and the cross-flowing continuous phase shears of the droplets [1,5,6,7]. A coarse emulsion is pressed through the membrane (sometimes several times) therewith applying shear to the droplets, and achieving a reduction of the droplet size [3].
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