Food small-molecule emulsifiers

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... 

It is apparent that real food emulsions are likely to behave in a more complex way than are simple model systems studied in the laboratory. This may be especially important when lecithins are present in the formulation. Although these molecules are indeed surfactants, they do not behave like other small-molecule emulsifiers. For example, they do not appear to displace proteins efficiently from the interface, even though the lecithins may themselves become adsorbed (123). They certainly have the capability to alter the conformation of adsorbed layers of caseins, although the way in which they do this is not fully clear it is possibly because they can fill in gaps between adsorbed protein molecules (124). In actual food emulsions, the lecithins in many cases contain impurities, and the role of these (which may also be surfactants) may confuse the way that lecithin acts (125). It is possible also for the phospholipids to interact with the protein present to form vesicles composed of protein and lecithin, independently of the oil droplets in the emulsion. The existence of such vesicles has been demonstrated (126), but their functional properties await elucidation. 

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... 

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]. 

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