Phase small-molecule emulsifiers

Feed—constituent interactions further affect retention (28,29). Dispersing agents and emulsifiers are partially retained because they attach to the dispersed phase. Small molecules may similarly adsorb onto larger particles. 

Therefore, to understand the behavior of food emulsions, we need to know as much as possible about these types of emulsifiers, because fliey may not behave exactly similarly to classical small-molecule emulsifiers. For example, phospholipid molecules can interact with each other to form lamellar phases or vesicles they may interact with neutral lipids to form a mono- or multi-layer around the lipid droplets, or they may interact with proteins which are either adsorbed or free in solution. Any or all of these interactions may occur in one food emulsion. The properties of the emulsion system depend on which behavior pattern predominates. Unfortunately for those who have to formulate food emulsions, it is rarely possible to consider the emulsion simply as oil coated with one or a mixture of surfactants. Almost always there are other components whose properties need to be considered along with those of the emulsion droplets themselves. For example, various metal salts may be included in the formulation (e.g. Ca " is nearly always present in food products derived from milk ingredients), and there may also be hydrocolloids present to increase the viscosity or yield stress of the continuous phase to delay or prevent creaming of the emulsion. In addition, it is very often the case, in emulsions formulated using proteins, that some of the protein is free in solution, having either not adsorbed at all or been displaced by other surfactants. Any of these materials (especially the metal salts and the proteins) may interact with the molecules... 

The structures of the interfacial layers in emulsion droplets might be expected to be simple when small-molecule emulsifiers are used, but this is not necessarily the case, especially when not one but a mixture of surfactant molecules is present. Although simple inter-facial layers may be formed where the hydrophobic moieties of the surfactants are dissolved in the oil phase, and the hydrophilic head groups are dissolved in the aqueous phase, it is also possible to form multilayers and liquid crystals close to the interface (78). These, of coiuse, depend on the natiue and the concentrations of the different siufactants. Interactions between surfactants generally enhance the stability of the emulsion droplets, because more rigid and structured layers tend to inhibit coalescence. Also, mixtiues of different surfactants having different HLB numbers appears to provide structured interfacial layers, presumably because of the different affinities of the siufactants for the oil-water interface (79). 

The possibility of the formation of nonisotropic surfaces on some types of emulsion droplets has been recently demonstrated. On interfaces of protein which have been treated with small-molecule emulsifiers, the protein is displaced. However, when insuffi dent emulsifier is added to cause desorption of all of the protein, there is a tendency for the different surfactants to form regions (i.e., to phase separate on the interface) (122). Clearly, such an interface offers the opportunity for directed aggregation because of the anisotropy of the surface. However, it depends on the presence of at least two surfactants. 

Miiny important systems, however, do not follow Smith-Ewart Case 2 kinetics n can be less than 0.5 if free radicals can diffuse from the particles into the aqueous phase. This radical transport is believed to follow chain transfer reactions to small molecules such as monomers, solvent, added chain transfer agents and even emulsifier. The resulting radicals are sufficiently mobile so that a fraction of them can diffuse out of the particles thus causing n to be less than 0.5. 

Proteins, on the other end of the scale of molecular complexity, act as emulsifiers but behave differently from the small molecules, because of their individual molecular structures, and, indeed, it is the particular proteins present which give many food emulsions their characteristic properties. Most, if not all, proteins in their native states possess specific three-dimensional structures which are maintained in solution, unless they are subjected to dismptive influence such as heating (6). When they adsorb to an oil-water interface, it is unlikely that the peptide chains of proteins dissolve significantly in the oil phase, as they are quite hydro-philic as a result of the presence of carboxyl or amido groups it is more likely that the major entities penetrating the interface are the side chains of the amino acids (Table 1). It is possible, for example, for an a-helical portion of a protein to have a hydrophobic side, created by the hydrophobic side chains which lie outside the peptide core of the helix. However, even proteins lacking such regular structures possess amino acids with hydrophobic side chains which will adsorb to the oil-water interface. When a protein is adsorbed, the structure of the protein itself will... 

The authors of this review (46) have used BSA along with monomeric emulsifiers, both in the inner and the outer interfaces (in low concentrations of up to 0.2 wt %), and found significant improvement both in the stability and in the release of markers as compared to the use of the protein in the external phase only (Fig. 13). It was postulated that while the BSA has no stability effect at the inner phase it has strong effect on the release of the markers (mechanical film barrier). On the other hand, BSA together with small amounts of monomeric emulsifiers (or hydrocolloids) serve as good steric stabilizers, improve stability and shelf-life, and slow down the release of the markers. The BSA plays, therefore, a double role in the emulsions as film former and barrier to the release of small molecules at the internal interface, and as steric stabilizer at the external interface. The release mechanisms involving reverse micellar trans-... 

Emulsion Formation. An oil-in-water emulsion is produced by homogenizing an oil phase and an aqueous phase together (see above). This emulsion is usually stabilized by an emulsifier that adsorbs to the oil-water interface, thereby facilitating droplet formation and retarding droplet aggregation. Typically, this emulsifier is either a small molecule surfactant (e.g. lecithin. Tween, Spans, etc) or a biopolymer (e.g. protein, polysaccharide, or protein-polysaccharide complex). In addition, a material that will... 

One of the most straightforward applications of polymer particles generated by MF methods includes the encapsulation and delivery of small molecules such as drugs, nutrients, food, or cosmetics ingredients. As explained in Section 8.4.2.1, an ingredient to be encapsulated is dissolved or dispersed in the dispersed phase, the mixture is emulsified, and a precursor droplet is transformed into a polymer particle. This approach has been demonstrated for uniformly gelled core-shell microgels derived from compound droplets [48]. 

The interfacial thickness of emulsion droplets is an important parameter affecting lipid oxidation reaction rates. Increasing interfacial membrane thickness can conceivably hinder the physical interaction between aqueous phase prooxidants (e.g., transition metals) and emulsified lipids(Chaiyasit et al., 2000 Silvestre et al., 2000). For example, Silvestre and co-workers (2000) showed that iron-catalyzed cumenehydroperoxide reduction, as well as salmon oil-in-water emulsion oxidation, was slower when Brij 700 was used in place of Brij 76. Brij 700 and 76 are small molecule surfactants with identical hydrophobic tail group lengths (CHjlCH lj -), but vary only with respect to the size of their polar head groups Brij 700 and Brij 76 consist of 100 and 10 oxyethylene head groups, respectively. Lower hydroperoxide decomposition and lipid oxidation rates in Brij 700-stabilized emulsions suggest that a thicker interfacial layer was able to act as a physical barrier to decrease lipid-prooxidant interactions (Silvestre et al., 2000). 

Several components of the organic phase contribute greatly to the character of the final product. The pore size of the gel is chiefly determined by the amount and type of the nonsolvent used. Dodecane, dodecanol, isoamyl alcohol, and odorless paint thinner have all been used successfully as nonsolvents for the polymerization of a GPC/SEC gel. Surfactants are also very important because they balance the surface tension and interfacial tension of the monomer droplets. They allow the initiator molecules to diffuse in and out of the droplets. For this reason a small amount of surfactant is crucial. Normally the amount of surfactant in the formula should be from 0.1 to 1.0 weight percent of the monomers, as large amounts tend to emulsify and produce particles less than 1 yam in size. 

---