Fats and Oils
Pages 29-45
DOI: https://doi.org/10.1094/9780913250907.003
ISBN: 0-913250-90-2
Abstract
Topics Covered
- Functions in Food Systems
- Amphiphilic (Polar and Nonpolar) Nature
- Emulsification
- Foaming
- Wetting
- Interactions with other Components
- Functional Properties
- Emulsification — HLB
- Antistaling — Complexing with Starch
- Protein Aggregation and Solution
- Emulsifier Types and Applications
- Emulsifiers
- Wetting Agents
- Dough Strengtheners
- Film Formers
- Regulatory Considerations
Introduction to Chapter
Oil and water do not mix; oil is nonpolar, whereas water is a polar liquid. If oil and water are shaken together, an emulsion is formed. In a familiar example, when a bottle containing olive oil and vinegar is shaken, the oil phase separates into droplets suspended in the vinegar. The oil is called the “dispersed phase,” while the vinegar is the “continuous phase” (Box 3-1). This example is an oil-in-water (O/W) emulsion. In other instances, for example, during the production of margarine, the water phase is dispersed in droplets in the oil phase, giving a water-in-oil (W/O) emulsion. If the mixture of oil and vinegar is left standing for a while, the two phases slowly separate, with the oil droplets rising to the top. The length of time for separation depends on the size of the droplets—large droplets rise faster than small ones. This process is called creaming. When the drops contact each other, they join together, or coalesce. The average drop size increases, and eventually a phase of oil becomes visible on the top. This is called emulsion “breakdown.”
If an emulsifier is present in the system, the drops formed during shaking are smaller and take longer to rise to the top. Thus, a longer time elapses before the emulsion creams, the droplets in the dispersed phase coalesce, and the emulsion breaks down. Emulsifiers are sometimes called surfactants, but not all surfactants are effective emulsifiers. The key point is that good emulsifiers promote the subdivision of the dispersed phase. The phase in which the emulsifier is soluble is usually the continuous phase—a water-soluble emulsifier such as Polysorbate 60 promotes an O/W emulsion, while an oil-soluble emulsifier such as monoglyceride promotes a W/O emulsion. This tendency is expressed by the hydrophilic-lipophilic balance (HLB), which is discussed later in this chapter.
The actions of oil, water, and emulsifier in the situations described above can be explained in terms of how energy, both intrinsic and applied, influences the mixture of oil and water. Energy exists at the interface between the two phases (this is γ, the interfacial tension, or surface tension). Energy can also be applied from outside in the form of mixing (e.g., stirring by hand or beating with an electric mixer). Each time the oil or water droplets are subdivided by mixing, more droplets are created and the amount of interfacial area increases. The lower the interfacial energy is to start with, the larger the amount of new interfacial area that can be created for a given amount of energy input. As the interfacial area increases, so does the interfacial energy. However, this is the energy that makes the droplets resist further subdivision. It makes the small droplets want to coalesce into larger droplets, leading eventually to separation of the oil and water phases. Added surfactant decreases the free energy at the oil-water interface, lowering interfacial tension and slowing the rate of coalescence. This chapter examines this process in more detail.
