Microstructure emulsions

Dubey NB, Windhab El (2013) Iron encapsulated microstructured emulsion-particle formation by prhhng process and its release kinetics. Journal of Food Engineering 115 198-206. 

J., ScHWESiNGEE, N., A microstructured device for the production of emulsions on demand, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6, pp. 159-167 (11-14 March 2002),... 

Although NMRI is a very well-suited experimental technique for quantifying emulsion properties such as velocity profiles, droplet concentration distributions and microstructural information, several alternative techniques can provide similar or complementary information to that obtained by NMRI. Two such techniques, ultrasonic spectroscopy and diffusing wave spectroscopy, can be employed in the characterization of concentrated emulsions in situ and without dilution [45],... 

In terms of measuring emulsion microstructure, ultrasonics is complementary to NMRI in that it is sensitive to droplet flocculation [54], which is the aggregation of droplets into clusters, or floes, without the occurrence of droplet fusion, or coalescence, as described earlier. Flocculation is an emulsion destabilization mechanism because it disrupts the uniform dispersion of discrete droplets. Furthermore, flocculation promotes creaming in the emulsion, as large clusters of droplets separate rapidly from the continuous phase, and also promotes coalescence, because droplets inside the clusters are in close contact for long periods of time. Ideally, a full characterization of an emulsion would include NMRI measurements of droplet size distributions, which only depend on the interior dimensions of the droplets and therefore are independent of flocculation, and also ultrasonic spectroscopy, which can characterize flocculation properties. 

K. B. Migler 2002, (Layered droplet microstructures in sheared emulsions finite-size effects), /. Colloid Interface Sci. 255, 391. 

N. C. Shapley, J. H. Walton, S. R. Dungan 2005, (Magnetic resonance imaging A technique to study flow and microstructure of emulsions), Braz. J. Chem. Eng. 22, 49. 

A typical characteristic of many food products is that these are multi-phase products. The arrangement of the different phases leads to a microstructure that determines the properties of the product. Mayonnaise, for example, is an emulsion of about 80% oil in water, stabilized by egg yolk protein. The size of the oil droplets determines the rheology of the mayonnaise, and hence, the mouthfeel and the consumer liking. Ice cream is a product that consists of four phases. Figure 1 shows this structure schematically. Air bubbles are dispersed in a water matrix containing sugar molecules and ice crystals. The air bubbles are stabilized by partial coalesced fat droplets. The mouthfeel of ice cream is determined by a combination of the air bubble size, the fat droplet size and the ice crystal size. 

In this level we specify the input (raw material) and the output (products) of the process. In this chapter, we will focus on single product processes only, but the method is not limited to this. The specification of the outputs includes a specification of the microstructure of the products, as well as other parameters, such as, the flavor profile and the microbiological status of the product. For the product microstructure one should specify the composition of the various phases of the product how the phases are arranged, and the interfacial composition. So for an emulsion one needs to specify ... 

The product microstructure is specified as follows. The product is an oil in water emulsion. The oil droplet size should be around 2pm. The emulsion is stabilized by two different emulsifiers, El and E2. Both emulsifiers should be at the interface in a certain ratio. Since there is an excess level of El, the remaining El should be dispersed in the water phase. The levels of the oil, El and E2 and the water phase are specified. The microstructure is shown schematically in Figure 3. 

Microemulsions are microstructured mixtures of oil, water, emulsifiers, and other substances. Since their structures differ in many ways from that of ordinary emulsions, it will be described separately. Liquid crystals (LC) are substances that exhibit special melting characteristics. Further, some surfactant-water-cosurfactant mixtures may also exhibit LC (lyotropic crystal) properties. 

The different microstructures, shown in Fig. 3, are highly dynamic aggregates. They can be detected by well established scattering techniques, like X-ray, light or neutron scattering [ 13]. Beside scattering techniques, the transitions between the microstructures can be detected from the changes of the viscosity of w/o-micro emulsion. For a diluted dispersion of spherical droplets without interactions, the relative viscosity is expected to obey the Einstein-relation ... 

The determination of the enzyme activity as a function of the composition of the reaction medium is very important in order to find the optimal reaction conditions of an enzyme catalysed synthesis. In case of lipases, the hydrolysis of p-nitrophenyl esters in w/o-microemulsions is often used as a model reaction [19, 20]. The auto-hydrolysis of these esters in w/o-microemulsions is negligible. Because of the microstructure of the reaction media itself and the changing solvent properties of the water within the reverse micelles, the absorbance maximum of the p-nitrophenol varies in the microemulsion from that in bulk water, a fact that has to be considered [82]. Because of this, the water- and surfactant concentrations of the applied micro emulsions have to be well adjusted. 

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

Polymer materials can easily be prepared from HIPEs if one or the other (or both) phases of the emulsion contain monomeric species. This process yields a range of products with widely differing properties. Additionally, as the concentrated emulsion acts as a scaffold or template, the microstructure of the resultant material is determined by the emulsion structure immediately prior to polymerisation. 

Very recently, ESR techniques have been employed to study the packing of surfactant molecules at the oil/water interface in w/o HIPEs [102,103], By including an amphiphilic ESR probe, which is adsorbed at the oil/water interfaces, it is possible to determine the microstructure of the oil phase from the distribution of amphiphiles between the films surrounding the droplets and the reverse micelles. It was found that most of the surfactant is located in the micelles, over a wide range of water fraction values. However, when the water content is very high (water droplets of the emulsion, to stabilise the large interfacial area created. 

The non-aqueous HIPEs showed similar properties to their water-containing counterparts. Examination by optical microscopy revealed a polyhedral, poly-disperse microstructure. Rheological experiments indicated typical shear rate vs. shear stress behaviour for a pseudo-plastic material, with a yield stress in evidence. The yield value was seen to increase sharply with increasing dispersed phase volume fraction, above about 96%. Finally, addition of water to the continuous phase was studied. This caused a decrease in the rate of decay of the emulsion yield stress over a period of time, and an increase in stability. The added water increased the strength of the interfacial film, providing a more efficient barrier to coalescence. 

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

Semenova, M.G., Belyakova, L.E., Dickinson, E., Eliot-Laize, C., Polikarpov, Yu.N. (2005). Caseinate interactions in solution and in emulsions effect of temperature, pH and calcium ions. In Dickinson, E. (Ed.). Food Colloids Interactions, Microstructure and Processing, Cambridge, UK Royal Society of Chemistry, pp. 209-217. 

Figure 3.2 Evolution of the microstructure of phase-separated biopolymer emulsion system containing pectin and 0.5 vt% heat-denatured (HD) whey protein isolate (WPI) stabilized oil droplets, (a) Composition 1U 3L (one-to-three mass ratio of upper and lower phases). The large circles are the water droplets (W), while the small circles are the oil droplets (O). This system forms a W2/W1-O/W1 emulsion, where O is oil, Wi is HD-WPI-rich and W2 is pectin-rich, (b) Composition 2U 2L. This system forms an 0/Wi/W2 emulsion, where O is oil, Wi is HD-WPI-rich and W2 is pectin-rich, (c) Composition 3U 1L. This system forms an 0/W]/W2 emulsion, where O is oil, Wi is HD-WPI-rich and W2 is pectin-rich. Reproduced from Kim et al. (2006) with permission.

There is now a solid body of available knowledge to indicate that the general features of biopolymer self-assembly in bulk aqueous solutions can account for various detailed aspects of the stability, rheology and microstructure of oil-in-water emulsions (and foams) stabilized by the same kinds of biopolymers (Dickinson, 1997, 1998 Casanova and Dickinson, 1998 Dickinson et al., 1997, 1998 Semenova et al., 1999, 2006 van der Linden, 2006 Semenova, 2007 Ruis et al., 2007). In particular, the richness of the self-assembly and surface-active properties of the... 

Hence, from the previously described light-scattering study of caseinate self-assembly in solution, we can postulate that heating/cooling not only alters the nature and strength of the physical (hydrophobic) interactions between emulsion droplets covered by caseinate. It most likely also transforms the nanoscale structural characteristics of the protein network in the bulk and at the interface, thereby affecting the viscoelastic and microstructural properties of the emulsions. 

In a recent study by Sun et al. (2007) of 20 vol% oil-in-water emulsions stabilized by 2 wt% whey protein isolate (WPI), the influence of addition of incompatible xanthan gum (XG) was investigated at different concentrations. It was demonstrated that polysaccharide addition had no significant effect on the average droplet size (d32). But emulsion microstructure and creaming behaviour indicated that the degree of flocculation was a sensitive function of XG concentration with no XG present, there was no flocculation, for 0.02-0.15 wt% XG, there was a limited... 

Figure 7.21 Effect of pH on microstructure of primary emulsions (no added polysaccharide) and secondaiy emulsions (0.1 or 0.5 wt% sodium alginate) based on 5 wt% oil, 0.45 vt% p-lactoglobulin, and 5 mM phosphate buffer. Reproduced from Pongsawatmanit et al. (2006) with permission.

Figure 7.22 Microstructure of acidified mixed emulsions (20 vol% oil, 0.5 wt% sodium caseinate) containing different concentrations of dextran sulfate (DS). Samples were prepared at pH = 6 in 20 mM imidazole buffer and acidified to pH = 2 by addition of HCl. Emulsions were diluted 1 10 in 20 mM imidazole buffer before visualization by differential interference contrast microscopy (A) no added DS (B) 0.1 wt% DS (C) 0.5 wt% DS (D) 1 wt% DS. Particle-size distributions of the diluted emulsions determined by light-scattering (Mastersizer) are superimposed on the micrographs, with horizontal axial labels indicating the particle diameter (in pm). Reproduced with permission from Jourdain et al. (2008).

Kerstens, S., Murray, B.S., Dickinson, E. (2006). Microstructure of p-lactoglobulin-stab-ilized emulsions containing non-ionic surfactant and excess free protein influence of heating. Journal of Colloid and Interface Science, 296, 332-341. 

Figure 8.4 Effect of replacing small fraction of p-lactoglobulin by sodium caseinate on microstructure of concentrated oil-in-w7ater emulsion (45 vol% oil, 3 wt% total protein, pH = 6.8, ionic strength = 0.03 M) heated for 6 min at 90 °C. Confocal micrographs were obtained with Rhodamine B as fluorescent protein stain (a) emulsion contains 3 wt% p-lactoglobulin (b) emulsion contains 2.85 wt% p-lactoglobulin + 0.15 wt% caseinate. Scale bar = 20 pm. Reproduced from Parkinson and Dickinson (2004) with permission.

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