Dispersion food emulsions

Another example of a food emulsion is the ice cream, in which the colloidal dispersion of ice particles is achieved together with tiny entrapped air bubbles in an emulsion consisting of fats, sugar, and thickening agents (polysaccharides). 

Benichou, A., Aserin, A., Garti, N. (2002). Protein-polysaccharide interactions for stabilization of food emulsions. Journal of Dispersion Science and Technology, 23, 93-123. 

Vincent, B. (1999). Dispersion stabilization and destabilization by polymers. In Dickinson, E., Rodriguez Patino, J.M. (Eds). Food Emulsions and Foams Interfaces, Interactions and Stability, Cambridge, UK Royal Society of Chemistry, pp. 19-28. 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

Because of the widespread applications of surface chemistry, practically all industries, knowingly or otherwise, make use of the principles of surface chemistry. Countless cosmetic and pharmaceutical products are emulsions—lotions, creams, ointments, suppositories, etc. Food emulsions include milk, margarine, salad dressings and sauces. Adhesive emulsions, emulsion paints, self-polishing waxes, waterless hand cleaners and emulsifiable insecticide concentrates are commonplace examples of emulsions, which fall within the province of surface chemistry. Other products winch function in accordance with the principles of smface chemistry include detergents of every variety, fabric softeners, antistatic agents, mold releases, dispersants and flocculants. 

Although mechanical parameters are important, this is not the only area of control. The selection of the correct mix of stabiliser components is also critical. Beverage emulsions are essentially different from food emulsions. Their application in a mobile, liquid phase at concentrations in the region of 0.1% results in the formation of a uniform dispersion of the component droplets, and in order to remain stable and to avoid the effects already mentioned, these droplets must remain discrete from each other and also not interact with other... 

Emulsions are colloidal dispersions of liquid droplets in another liquid phase, sometimes stabilized by surface active agents. Emulsions thus consist of a discontinuous phase, dispersed in a continuous phase. The most common types of emulsions are water-in-oil (W/O) in which oil is the continuous phase, and oil-in-water (OAV) in which water forms the continuous phase. However, this traditional definition of an emulsion is too narrow to include most food emulsions. For example, in foods the dispersed phase may be partially solidified, as in dairy products or the continuous phase may contain crystalline material, as in ice cream. It may also be a gel, as in several desserts. In addition to this, air bubbles may have been incorporated to produce the desired texture. 

It is not possible to discuss all the methods available for characterizing foods critically and systematically in a single volume. Methods pertaining to interfaces (food emulsions, foams, and dispersions), fluorescence, ultrasonics, nuclear magnetic resonance, electron spin resonance, Fourier-transform infrared and near infrared spectroscopy, small-angle neutron scattering, dielectrics, microscopy, rheology, sensors, antibodies, flavor and aroma analysis are included. 

The structure of the interfacial layers in food colloids can be quite complex as these are usually comprised of mixtures of a variety of surfactants and all are probably at least partly adsorbed at interfaces which even individually, can form complex adsorption layers. The layers can be viscoelastic. Phospholipids form multi-lamellar structures at the interface and proteins, such as casein, can adsorb in a variety of conformations [78]. Lecithins not only adsorb also at interfaces, but can affect the conformations of adsorbed casein. The situation in food emulsions can be complicated further by the additional presence of solid particles. For example, the fat droplets in homogenized milk are surrounded by a membrane that contains phospholipid, protein and semi-solid casein micelles [78,816], Similarly, the oil droplets in mayonnaise are partly coated with granular particles formed from the phospho and lipo-protein components of egg yolk [78]. Finally, the phospholipids can also interact with proteins and lecithins to form independent vesicles [78], thus creating an additional dispersed phase. 

The nature of the colloidal dispersion can have important influences on other food properties. For example, a 50/50 % emulsion of oil (fat) and water has a very different thermal properties in O/W versus W/O form. The O/W emulsion would be expected to have the greater thermal conductivity, water being the external phase and, other factors being equal, should freeze at a faster rate [811]. O/W food emulsions tend to be quite fluid, whereas W/O food emulsions tend to be more viscous, sometimes solid-like. 

Food grade surfactants are, in general, not soluble in water, but they can form association structures in aqueous medium that are liquid crystalline in nature. These liquid crystalline structures are produced by heating the solid emulsifier (which is dispersed in water) to a temperature above its Krafft temperature. On cooling such a system, a gel phase is produced which becomes incorporated with the emulsion droplets. These gel phases produce the right consistency for many food emulsions. 

Very often, the microstructure and the macroscopic states of dispersions are determined by kinetic and thermodynamic considerations. While thermodynamics dictates what the equilibrium state will be, kinetics determine how fast that equilibrium state will be determined. While in thermodynamics the initial and final states must be determined, in kinetics the path and any energy barriers are important. The electrostatic and the electrical double-layer (the two charged portions of an inter cial region) play important roles in food emulsion stability. The Derjaguin-Landau-Verwey-Oveibeek (DLVO) theory of colloidal stability has been used to examine the factors affecting colloidal stability. 

Emulsifier/stabilizer systems are normally used to make stable food emulsions. Thus, lecithin is generally not called on to handle the entire emulsification, but it works in combination with other emulsifiers and stabilizing polymers such as proteins, starches, and gums (31). Lecithin will break up (emulsify) the particles, and a stabilizer (water-soluble polymer, etc.) will hold the particles in a dispersed orientation when a stable emulsion is formed. 

Disperse phase volume fraction. The viscosity of food emulsions tends to increase with increased disperse phase volume fraction (Figure 10). The viscosity increases relatively slowly, with 4> at low droplet concentrations, but increases steeply when the droplets become closely packed together. At higher droplet concentrations, the particle network formed has predominantly elastic characteristics. 

A new method for droplet size measurement, using a bench-top pulsed-field-gradient NMR spectrometer operating in the time domain, has been reported (18). The continuous water phase is successfully suppressed by gradient pulses in order to measure the dispersed oil phase. Simulations show that for most common oil/water food emulsions the influence of droplet diffusion is negligible due to a rather large droplet size or a high viscosity of the continuous water phase. 

Many foodstuffs consist of gelled emulsions, due to deliberate addition of gums and thickeners to increase the mass thickness (e.g., sausages) or due to denaturation of proteins to form protein micelles (e.g., cheese). Food emulsions containing water in oil have an internal water phase that is dispersed as droplets within an oil (or lipid) phase. The microorganisms are mostly found in the droplets (Verrips and Zaalberg, 1980 ... 

Several industrial systems involve emulsions, of which the following are worthy of mention. Food emulsions include mayonnaise, salad creams, deserts, and beverages, while personal care and cosmetics emulsions include hand creams, lotions, hair sprays, and sunscreens. Agrochemical emulsions include self-emulsifiable oils that produce emulsions on dilution with water, emulsion concentrates with water as the continuous phase, and crop oil sprays. Pharmaceutical emulsions include anaesthetics (O/W emulsions), hpid emulsions, and double and multiple emulsions, while paints may involve emulsions of alkyd resins and latex. Some dry-cleaning formulations may contain water droplets emulsified in the dry cleaning oil that is necessary to remove soils and clays, while bitumen emulsions are prepared stable in their containers but coalesce to form a uniform fihn of bitumen when apphed with road chippings. In the oil industry, many crude oils (e.g.. North sea oil) contain water droplets that must be removed by coalescence followed by separation. In oil slick dispersion, the oil spilled from tankers must be emulsified and then separated, while the emulsification of waste oils is an important process for pollution control. 

B. L. Wedzicha. Distribution of low-molecular-weight food additives in dispersed systems. In E. Dickinson, G. Stainsby, eds. Advances in Food Emulsions and Foams. Elsevier, London, 1988, pp. 329-371. 

The functional requirements of practical food emulsions are not complete stability, but rather controlled instability. Destabilizing reactions of food emulsions involve creaming, flocculation, and coalescence. An emulsion would cream or sediment if the dispersed phase is sufficiently different in density from the continuous phase. Creaming can be reduced by increasing the viscosity of the aqueous phase or be enhanced by increasing the particle size of oil droplets or lowering the density of the oil phase. 

Pectin is extracted commercially from citrus peel (lemon, lime and grapefruit) and apple pomace.1,2 The food industry is the most important field of application of extracted pectin. Pectins from different sources are widely used to stabilize food emulsions and dispersions in products such as fruit drinks, and fruit and tomato pastes.3 Pectin can form gels under certain circumstances and it... 

Emulsions are dispersions of one liquid phase in the form of fine droplets in another immiscible liquid phase. The immisciable phases are usually oil and water, so emulsions can be broadly classified as oil-in-water or water-in-oil emulsions, depending on the dispersed phase. Some typical food emulsions are mild cream, ice cream, butter, margarine, salad dressing, and meat emulsions. The results from rheological measurements can allow for a better understanding of how various emulsifiers/stabilizers interact to stabilize emulsions. Understanding the effect of additives such as food... 

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