Overview Of Homogenization
The formation of an emulsion may involve a single step or a number of consecutive steps, depending on the nature of the starting material and the method used to create it. Prior to converting separate oil and aqueous phases into an emulsion, it is usually necessary to disperse the various ingredients into the phase in which they are most soluble. Oil-soluble ingredients, such as vitamins, colors, antioxidants, and surfactants, are usually mixed with the oil, whereas water-soluble ingredients,...
Table 51
Summary of the Instruments Used for Measuring Surface and Interfacial Tensions Du Nouy ring Wilhelmy plate Pendant drop Sessile drop Spinning drop Capillary rise Dynamic Maximum bubble pressure Oscillating jet Drop volume Surface waves Du Nouy ring Wilhelmy plate Pendant drop Sessile drop Spinning drop Drop volume Pendant drop Spinning drop FIGURE 5.13 Du Nouy ring method of determining the interfacial and surface tension of liquids. FIGURE 5.13 Du Nouy ring method of determining the...
HighPressure Valve Homogenizers
High-pressure valve homogenizers are the most commonly used method of producing fine emulsions in the food industry. Like colloid mills, they are more effective at reducing the size of the droplets in a preexisting emulsion than at creating an emulsion directly from two separate liquids Pandolfe 1991, 1995 . A coarse emulsion is usually produced using a highspeed blender and is then fed directly into the input of the high-pressure valve homogenizer. The homogenizer has a pump which pulls the...
Practical Implications Of Interfacial Phenomena
To conclude this chapter, a brief outline of some of the most important practical implications of interfacial phenomena for food emulsions is presented. One of the most striking features of food emulsions when observed under a microscope is the sphericity of the droplets. Droplets tend to be spherical because this shape minimizes the energetically unfavorable contact area between oil and water molecules, which is described by the Laplace equation Equation 5.4 . Droplets become nonspherical when...
Colloidal Interactions
Food emulsions are microheterogeneous materials that contain a variety of different structural entities which range in size, shape, and physicochemical properties, including atoms, molecules, molecular aggregates, micelles, emulsion droplets, crystals, and air cells Dickinson and Stainsby 1982, Dickinson 1992 . Many of these structural entities have at least one dimension that falls within the colloidal size range i.e., between a few nanometers and a few micrometers see Figure 1.8 . The...
Interdroplet Pair Potential 1
When the separation between two droplets is small compared to their size h lt lt rd , the interdroplet pair potential due to exclusion of the colloidal particles from the depletion zone is given by the following expression Sperry 1982 where POSM is the osmotic pressure arising from the exclusion of the colloidal particles and rc is the radius of the colloidal particles. The osmotic pressure difference is given by the following equation Hiemenz 1986 W I1 2M 3.21 Here, C, M, and v are the...
Capillary Rise And Meniscus Formation
The surface tension of a liquid governs the rise of liquids in capillary tubes and the formation of menisci curved surfaces at the top of liquids Hiemenz 1986, Hunter 1986 . When a glass capillary tube is dipped into a beaker of water, the liquid climbs up the tube and forms a curved surface Figure 5.10 . The origin of this phenomenon is the imbalance of intermolecular forces at the various surfaces and interfaces in the system Evans and Wennerstrom 1994 . When water climbs up the capillary...
POLYMERIC STERIC INTERACTIONS 351 Polymeric Emulsifiers
In Section 3.3, we saw that van der Waals interactions always operate between emulsion droplets and that these interactions are strong enough to cause droplets to aggregate, unless there is a sufficiently strong repulsive interaction to prevent them from coming close together. When emulsion droplets are surrounded by a layer of electrically charged emulsifier molecules, they may be stabilized against aggregation by electrostatic repulsion Section 3.4 . Nevertheless, many food emulsions are...
Hydrophobic Interactions
Compared to the other major forms of colloidal interaction, the contribution of hydrophobic interactions to emulsion stability has largely been ignored by emulsion scientists. Nevertheless, this type of interaction is of great importance in many types of foods and has recently been shown to promote droplet flocculation in protein-stabilized emulsions Monahan et al. 1996, Demetriades et al. 1997b . Hydrophobic interactions are important when the surfaces of the droplets have some nonpolar...
Energy Input
The size of the droplets in an emulsion can be reduced by increasing the amount of energy supplied during homogenization as long as there is sufficient emulsifier to cover the surfaces of the droplets formed . The energy input can be increased in a number of different ways depending on the nature of the homogenizer. In a high-speed blender, the energy input can be enhanced by increasing the rotation speed or the length of time that the sample is blended. In a high-pressure valve homogenizer, it...
Membrane Homogenizers
An emulsion is formed by forcing one immiscible liquid into another through a glass membrane which contains a uniform pore size Figure 6.10 . The size of the droplets formed FIGURE 6.10 Batch version of a membrane homogenizer. depends on the diameter of the pores in the membrane and the interfacial tensions between the oil and water phases Kandori 1995 . Membranes can be manufactured with different pore diameters so that emulsions with different droplet sizes can be produced Kandori 1995 . The...
DEPLETION INTERACTIONS 361 Origin of Depletion Interactions
Many food emulsions contain small colloidal particles that are dispersed in the continuous phase which surrounds the droplets Figure 3.17 . These colloidal particles may be surfactant FIGURE 3.17 An attractive depletion interaction arises between emulsion droplets when they are surrounded by small nonadsorbing colloidal particles. FIGURE 3.17 An attractive depletion interaction arises between emulsion droplets when they are surrounded by small nonadsorbing colloidal particles. micelles formed...
Info Oku
colloid formed in many food emulsions, we will focus principally on their properties Dickinson and McClements 1995 . 4.5.2. Functional Properties 4.5.2.1. Critical Micelle Concentration A surfactant forms micelles in an aqueous solution when its concentration exceeds some critical level, known as the critical micelle concentration or CMC Myers 1988 . Below the CMC, the surfactant molecules are dispersed predominantly as monomers, but once the CMC is exceeded, any additional surfactant molecules...
Sessile and PendantDrop Methods
The sessile- and pendant-drop methods can be used to determine the static surface and interfacial tensions of liquids Hunter 1986, Couper 1993 . The shape of a liquid droplet depends on a balance between the gravitational and surface forces. Surface forces favor a spherical droplet because this shape minimizes the contact area between the liquid and its surroundings. On the other hand, gravitational forces tend to cause droplets to become flattened if they are resting on a solid surface or...
Info Ekn
FIGURE 4.5 The critical size of a nucleus required for crystal growth depends on a balance between the volume and surface contributions to the free energy of nuclei formation. nuclei. At a certain critical nucleus radius r , the overall free energy has a maximum value given by This equation can be rearranged to give an expression for the critical radius of the nucleus which must be achieved for crystallization to occur If a nucleus that has a radius below this critical size is formed, it will...
Molecular Characteristics
The principal role of surfactants in food emulsions is to enhance their formation and stability Charalambous and Doxastakis 1989, Dickinson 1992, Hasenhuettl and Hartel 1997 however, they may also alter emulsion properties in a variety of other ways e.g., by interacting with proteins or polysaccharides, by forming surfactant micelles, or by modifying the structure of fat crystals Dickinson and McClements 1995, Bergenstahl 1997, Bos et al. 1997, Deffenbaugh 1997 . By definition, a surfactant is...
Surfactant Classification
A food manufacturer must consider a variety of factors when selecting a surfactant for a particular product, including its legal status as a food ingredient its cost the reliability of the supplier the consistency of its quality from batch to batch its ease of handling and dispersion its shelf life its compatibility with other ingredients the processing, storage, and handling conditions it will experience and the expected shelf life and physicochemical properties of the final product. How does...
Emulsion Properties
1.3.1. Dispersed-Phase Volume Fraction The concentration of droplets in an emulsion is usually described in terms of the dispersed-phase volume fraction , which is equal to the volume of emulsion droplets VD divided by the total volume of the emulsion VE VDIVE. Knowledge of the dispersed-phase volume fraction is important because the droplet concentration influences the appearance, texture, flavor, stability, and cost of emulsion-based food products. In some situations, it is more convenient to...
Emulsion Science In The Food Industry
Many natural and processed foods consist either partly or wholly as emulsions or have been in an emulsified state at some time during their production such foods include milk, cream, butter, margarine, fruit beverages, soups, cake batters, mayonnaise, cream liqueurs, sauces, desserts, salad cream, ice cream, and coffee whitener Friberg and Larsson 1997, Krog et al. 1983, Jaynes 1983, Dickinson and Stainsby 1982, Dickinson 1992, Swaisgood 1996 . Emulsion-based food products exhibit a wide...
Interdroplet Pair Potential
Polymeric steric interactions arise when emulsion droplets get so close together that the emulsifier layers overlap Figure 3.15 . This type of interaction can be conveniently divided into two contributions Hiemenz 1986, Hunter 1986 Wsteric h elastic h mix h 3.16 The elastic contribution is due to the compression of the interfacial membrane, whereas the mixing contribution is due to the intermingling of the polymer chains Figure 3.15 . If it is assumed that the polymer molecules in the layers...
Table of Contents
1.1. Emulsion Science in the Food Industry 1.2. General Characteristics of Food Emulsions 1.2.1. Definitions 1.2.2 Mechanisms of Emulsion Instability 1.2.3. Ingredient Partitioning in Emulsions 1.2.4. Dynamic Nature of Emulsions 1.2.5. Complexity of Food Emulsions 1.3.1. Dispersed-Phase Volume Fraction 1.3.2. Particle Size Distribution 1.4. Hierarchy of Emulsion Properties 1.5. Investigation of Emulsion Properties 2.3. Origin and Nature of Molecular Interactions 2.3.2. Electrostatic...