Emulsions are formed. Emulsions

Emulsion is a dosage form homogeneous in appearance, consisting of mutually insoluble finely dispersed liquids, for internal, external or injection use.

The production of emulsions is regulated by the State Pharmacopoeia.

Emulsions are microheterogeneous systems. The sizes of liquid droplets in emulsions range from 0.1 to 50 microns. The dispersed phase can be not only liquid, but also gas.

Medicinal substances in the dosage form “Emulsion” are prescribed for the purpose of:

Mask an unpleasant taste or smell (for example, castor oil, essential oils, etc.);

Facilitate the dosed intake of viscous, thick liquids (vinylene, castor oil, etc.);

Soften the irritating effect of certain medicinal substances (chloral hydrate, bromides, methyluracil, etc.);

Ensure the absorption of the oil phase in the stomach from emulsions of the first kind, accelerate the hydrolysis of dispersed fats by enzymes of the gastrointestinal tract;

Accelerate the absorption of oils in a finely dispersed state when administered enterally.

Emulsions are classified:

1. By use: for external use (nutritive and therapeutic enemas, cleansing emulsions, cosmetic milk, etc.); for internal use (medicine); for injection (emulsions for parenteral nutrition).

2. Composition: simple (oil - lipophilic liquid, emulsifier water - hydrophilic liquid); complex.

3. According to the source material: oil; seed.

4. By concentration: diluted (up to 0.1% of the liquid phase, for example, aromatic waters). They can be stable without adding a stabilizer, due to their high dispersion and low concentration of the dispersed phase; concentrated (more than 5% of the liquid phase) - the majority of emulsions used in medical practice.

To stabilize concentrated emulsions, the addition of a stabilizer (emulsifier) ​​is required; highly concentrated1) emulsions (more than 70% liquid phase).

5. By type, emulsions of the first kind (oil/water) _ dispersed phase (oil or lipophilic liquid) in the form of droplets distributed in an aqueous (or hydrophilic) dispersion medium. Emulsions of this type are more liquid and resemble milk in appearance. Use internally, externally, injection emulsions of the second type (water/oil) - the dispersed phase (water or hydrophilic liquid) in the form of droplets is distributed in an oily (or lipophilic) dispersed medium. Emulsions of this type are more viscous and thick. In appearance they resemble soft butter. Mainly used externally: ointments, liniments, creams.

Emulsions must be homogeneous and shelf stable; resistant to mechanical stress (should not delaminate during centrifugation at a rotation speed of 1.5 thousand min-1); withstand exposure to high (up to 50 °C) and low temperatures; provide optimal pharmacological effect.

In emulsions during storage, coalescence is possible - the process of enlargement and merging of droplets of the dispersed phase (loss of aggregative stability). The aggregative stability of emulsions, as well as solutions of protected colloids and suspensions, is understood as the ability of the dispersed phase (liquid droplets or gas bubbles) to maintain a uniform distribution in a dispersed medium for as long as possible. When phase droplets merge into a continuous layer, the emulsion stratifies - it is divided into two immiscible layers and is not restored when shaken (loss of aggregative and kinetic stability).

Emulsions separate under the influence of strong electrolytes, dehydrating substances (ethanol, distilled glycerin, sugar syrup, etc.), acidic and alkaline substances, environmental factors, mechanical stress, and temperature.

Considering the lack of affinity of the dispersed phase for the medium, it is not possible to obtain stable concentrated and, especially highly concentrated emulsions, only by reducing the particle size (as in the case of suspensions of hydrophilic substances with affinity for the medium) without adding stabilizers. As the particles of the dispersed phase decrease, the free interphase energy (Gibbs energy) increases, which, in the absence of affinity of particles of the dispersed phase to the medium, tends to decrease due to the merging of particles (reducing the specific surface area of ​​the dispersed phase). Stabilize the system (reduce the Gibbs energy) while maintaining high dispersion of particles of the dispersed phase is achieved by reducing the value of interfacial tension.

This role is played by surfactants, whose molecules are adsorbed at the phase interface (liquid/liquid, liquid/gas), forming a film of emulsifier molecules that firmly envelops the particles of the dispersed phase.

The emulsifier molecules are arranged in a strictly defined manner depending on the nature of the groups of its molecules. The hydrophilic groups of the emulsifier are always oriented towards the aqueous phase and are immersed in it. Non-polar regions of molecules, such as hydrocarbon chains, are always oriented towards the oil phase.

For more information about the properties of surfactants, see Chapter. 5.

The task of producing aggregation-stable emulsions comes down primarily to the selection of an effective emulsifier specific to a given type of emulsion.

Due to the instability of the emulsion, the pharmacy prepares it ex tempore.

Milk is a typical natural emulsion of fat in water - the fat phase is found in the milk plasma in the form of small drops (fat globules) of more or less regular shape, surrounded by a protective lipoprotein membrane. The presence of fat in milk in a finely dispersed form plays an important role in the process of its absorption by newborns, as well as during the technological processing of milk.

Based on the polarity of the dispersed phase and the dispersion medium, emulsions are divided into direct (oil in water) and reverse (water in oil). Depending on the concentration of the dispersed phase in the system, diluted, concentrated and highly concentrated emulsions are distinguished.

Dilute emulsions are similar in properties to lyophobic colloidal solutions. Their stability is due to the electrical charge of the particles (droplets). When the system loses stability, the droplets spontaneously form aggregates, followed by their merging (coalescence) with each other.

The size and number of fat globules in milk are variable and depend on the breed of animal, stage of lactation, feed rations and other factors. 1 ml of milk contains from 1.5 to 3 billion fat globules, their average diameter is from 2 to 2.5 microns with fluctuations from 0.1 to 10 microns or more. The sizes of fat globules are of practical importance, since they determine the degree of transition of fat into the product during the production of cream, butter, cheese, cottage cheese, etc.

The physical stability of fat globules in milk and dairy products, their behavior during cream settling and technological processing (homogenization, pasteurization, etc.) mainly depend on the composition and properties of their shells.

The shell of fat globules consists of lipids and proteins. These components, oriented in a certain way on the surface of the balls, stabilize the milk fat emulsion. The lipid fraction of the shell contains phospholipids (phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, etc.), high-melting triglycerides, cerebrosides, cholesterol, carotenes, vitamin A, etc. The protein components of the shell are divided into two fractions based on solubility in water (diluted saline solutions). One fraction of structural proteins is poorly soluble in water, contains about 14% nitrogen, and differs in amino acid composition from milk proteins (contains less lysine, valine, leucine, glutamic and aspartic acids and more arginine).

Another water-soluble protein fraction includes a glycoprotein with a high (about 18%) carbohydrate content and various enzymes.

Enzymes of the fat globule shell include xanthine oxidase, alkaline and acid phosphatases, cholinesterase, etc.

In addition to lipids and proteins, mineral elements were found in the shell of fat globules: Cu, Fe, Mo, Zn, Ca, Mg, Se, Na and K. It was found that from 5 to 25% of native milk copper and from 28 to 59% are associated with the shell. native iron (Cu content in 1 g of shell ranges from 5 to 25 μg, Fe - from 70 to 150 μg).

According to electron microscopic studies, the shell of the fat globule consists of two layers of different composition - an internal thin layer, tightly adjacent to the crystalline layer of high-melting triglycerides of the fat globule, and an external loose (diffuse) layer, easily desorbed during technological processing of milk.

The inner layer (membrane, matrix) has a thickness of 5 to 10 nm, formed from the plasma membrane of the secretory cell of the mammary gland during the process of secretion.

The emulsion of fat globules in milk is quite stable. Cooling of milk, mechanical action of pumps, mixers, heating to relatively high temperatures slightly change the composition, physico-chemical properties of the shells of fat globules, without disturbing the stability of the fat emulsion.

When processing milk, the first thing that changes is the outer layer of the shell. It is known that in freshly milked milk the shells have an uneven, rough surface and a fairly large thickness of the outer layer. After mixing, shaking and storing the milk, the fat globule shells become smoother and thinner. These changes are due to the desorption of lipoprotein micelles from the membranes into the plasma. Simultaneously with the desorption of micelles, sorption of proteins and other components of milk plasma occurs on the surface of the membrane of fat globules. The processes of desorption - sorption during stirring and cooling can cause some changes in the composition and surface properties of the shells, which leads to a decrease in their strength and partial rupture. During the heat treatment of milk, not only a significant restructuring of the structural components of the shell is observed, but also partial denaturation (conformational rearrangement) of membrane proteins, which contributes to a further decrease in the stability of the shells of fat globules.

The shells can be destroyed relatively quickly as a result of special mechanical action, used, for example, in the production of butter, as well as the action of chemicals (concentrated acids, alkalis, amyl alcohol).

The stability of milk fat emulsion can be explained by the following factors. The first important factor in the stability of dilute emulsions stabilized by an emulsifier is, as is known, the appearance of an electrical charge on the surface of fat droplets.

The shells of fat globules contain polar groups on the surface: phosphate groups of phosphatidylcholine and other phospholipids, carboxyl groups, amino groups, COOH groups of sialic acid of protein and carbohydrate components. A total negative charge is created on the surface of the balls (their isoelectric state occurs at a milk pH of about 4.5). Cations Ca2+, Mg2+, etc. are added to the negatively charged groups. As a result, an electric double layer is formed, similar to the layer that appears on the surface of particles of typical hydrophobic colloids. Thus, at the phase boundary between fat globules, electrostatic repulsive forces act that exceed the attractive forces (energy barrier). An additional stabilizing effect is exerted by the hydration shell formed around the polar groups of the membrane components.

Among all the structural components of the fat globule shell, glycoproteins and phospholipids are especially important for stabilizing the milk fat emulsion. Thus, after treating the shells with proteinases that destroy glycoproteins, the stability of the emulsion decreases, and after removing the polar groups of phospholipids using phospholipase C, it drops sharply and coalescence of fat globules occurs.

The second factor in the stability of emulsions is the creation of a structural-mechanical barrier at the interface. A study of the structural and mechanical properties of the shells of fat globules showed that they have increased structural viscosity, mechanical strength and elasticity, and therefore can serve as a structural and mechanical barrier that prevents the merging of the globules.

Thus, the stability of milk fat emulsion is determined by thermodynamic (the presence of a double electrical layer and a hydration shell) and structural-mechanical factors. The structural-mechanical factor is the most powerful factor in stabilizing concentrated emulsions, which include, for example, high-fat cream.

Therefore, to ensure the stability of the fat emulsion of milk and cream during the production of dairy products, it is necessary to strive to preserve the shells of the fat globules intact and not reduce the degree of their hydration. For this purpose, it is necessary to reduce to a minimum mechanical impacts on the dispersed phase of milk during transportation, storage and processing, avoid its foaming, properly carry out heat treatment (long exposure at high temperatures can cause significant denaturation of the structural proteins of the shell and damage to its integrity), as well as widely apply additional fat dispersion by homogenization.

If during the production of most dairy products the process engineer is faced with the task of preventing aggregation and coalescence of fat globules, then when producing butter he is faced with the opposite task - to destroy (demulsify) the stable fat emulsion and separate the dispersed phase from it.

Emulsions find a variety of applications in food production. Some food products and food industry products are emulsions. Emulsions include milk, cream, butter, sour cream, margarine, i.e. fat-containing foods.

The composition of milk (O/W emulsion) includes liquid and partly solid fats, which represent a dispersed phase, and the aqueous dispersion medium contains proteins, various salts and sugar. Cream is a more concentrated emulsion compared to milk. Margarine is a concentrated W/O emulsion in which water serves as the dispersed phase, and the dispersion medium is edible fat purified from impurities. Edible fat is obtained from soybean, sunflower, cottonseed or corn oil. In addition, vitamins, coloring and other substances are added to margarine. Mayonnaise is a concentrated O/W vegetable oil emulsion. The dispersion medium is water containing egg yolk, vinegar, mustard, sugar, and spices. Butter is a highly concentrated structured system, which includes direct and reverse emulsions - mostly O/W and partly W/O.

Emulsions are widely used in food technology. Fats are introduced into the dough in the form of an O/W emulsion, which significantly improves the quality of bread and bakery products.

It should be noted that emulsions play an important role in the life of the human body. The composition of blood includes an emulsion, the dispersed phase of which is erythrocytes, and proteins act as emulsifiers. Fats, an essential component of food, are insoluble in water and are absorbed only in an emulsified state.

Milk, cream, sour cream, and butter are emulsions and do not require additional emulsification. Vegetable oil and animal fat do not form emulsions in an aqueous environment. Therefore, before assimilation of such products, they are first transferred to an emulsified state. Emulsification occurs first in the stomach and then in the duodenum. Bile acts as an emulsifier, which contains bile acids - monocarboxylic hydroxy acids belonging to the class of steroids. At relatively high pH values ​​of 8.0-8.5, bile salts are formed. These salts are good emulsifiers.

The interfacial surface tension of water at the interface with oil σlj is approximately 40 mJ/m2. Solutions of bile acids reduce it hundreds of times, which ensures that conditions (15.2) and (15.3) are met - the system turns from lyophobic to lyophilic; Spontaneous dispersion of fat occurs in the stomach, and the resulting emulsion will be stable. Dispersion of fat and formation of emulsions is facilitated by peristaltic movement of the intestines. As a result, a direct emulsion of fat in water of the O/W type is formed. Such an emulsion enters the lymph and blood through the walls of the small intestines and is absorbed by the body.

Drugs are often also emulsions. To introduce them into the body through the mouth, it is recommended to use direct O/W emulsions. Medicines are introduced into the body through the skin in the form of reverse emulsions of the W/O type, since the skin is an obstacle to water and substances dissolved in it and easily allows other liquids to pass through.

Emulsions are widely used not only in food, but also in a number of other industries. Thus, the main process of soap making is associated with the formation of a direct O/W emulsion. Emulsification occurs in the dehydration of crude oil, in the production of petroleum products and cleaning of oil tanks, in the production of asphalt mixtures and the processing of natural rubber, in the production of film and photographic materials, in the production of greases and coolants for metal processing, as well as in a number of other technological processes.

Synthetic varnishes, which are emulsions of synthetic rubber and resin, are used for gluing and gluing paper, impregnating fabrics, and for preparing leather substitutes and various rubber products. Emulsion paints are non-toxic and fire-explosion-safe. For spraying plants, preparations are usually used in the form of emulsions. Natural emulsions include a number of valuable plant and animal products.

In industrial conditions, it is often necessary to combat the resulting emulsions. For example, during the dehydration of various petroleum products, in the paper and leather industries to prevent the precipitation of dispersed phase droplets on the fiber.

Chapter 16

FOAM

Foams differ from other dispersed systems in their mobility and ability to change the phase interface. A rapid decrease in the phase interface reduces the lifetime of the foam and necessitates the use of surfactants to maintain the stability of foams. A significant increase in the specific surface area of ​​the moving phase interface gives foams special properties.

Foams are formed in some technological processes, as well as under conditions of using various drugs.

In the process of producing an emulsion, especially by dispersion methods, drops of both one and another liquid are inevitably formed. However, over time, drops of one liquid are preserved and gradually accumulate, while drops of another coalesce almost instantly. If oil droplets accumulate, a direct emulsion (O/W) is formed, if water – a reverse emulsion (W/O) is formed. The type of emulsion formed depends on a number of factors, but is largely determined by the nature of the emulsifier. Following Bancroft's rule, we can say that the liquid that dissolves the emulsifier better or wets it better (if it is a powder) is a dispersion medium. Thus, knowing the nature of the emulsifier, it is possible to predict the type of emulsion formed. However, such an estimate is very approximate, especially if the emulsion is multicomponent.

There are several experimental methods for determining the type of emulsions.

DILUTION METHOD

A drop of emulsion is introduced into a test tube with water, which, with gentle shaking, is evenly distributed in the volume of water if it is an O/W emulsion. If the emulsion is reverse (W/O), then the drop does not disperse. This test gives better results in the case of dilute emulsions.

METHOD OF WETTING HYDROPHOBIC

SURFACES

When a drop of emulsion is applied to a paraffin plate, the drop spreads if the dispersion medium is oil (W/O emulsion).

DEFINITION OF CONTINUOUS PHASE

A drop of the emulsion is placed on a microscope slide next to several crystals of dye dissolved in water. The plate is tilted so that the drop and the dye are in contact. If the continuous medium (water) appears to be colored, it is an O/W emulsion. Otherwise, the experiment is repeated with a fat-soluble dye, proving that the emulsion – V/M type. Water-soluble dyes are, for example, methyl orange and brilliant blue, and oil-soluble – Sudan III and magenta. This test can be carried out by pouring a certain amount of emulsion into a test tube and adding a few crystals of a water-soluble dye. Uniform coloring of the liquid will indicate that it is an O/W emulsion. Tronner and Bassus (1960) developed this method. On filter paper mugs moistened with 20% – m cobalt chloride solution and then dried, they placed a drop of emulsion. O/W emulsion causes a rapid appearance of pink color; no color changes were observed with W/O emulsion. If there is a mixture of O/W and W/O emulsions – slowly appears weakly – pink coloring.

CONDUCTIVITY MEASUREMENT

Two electrodes connected to an alternating current source and a neon lamp are placed in the emulsion. If the emulsion is O/W type – the neon lamp lights up because the aqueous continuous medium has much greater electrical conductivity than the oil one.

LESSON PLAN 26.

Teacher: Chumachenko E.V.

Topic: “General characteristics of coarse systems, their classification. Characteristics of emulsions".

Goals:

Educational: study the properties of coarse systems and their classification.

Educational: instilling interest in the discipline.

Developmental: developing the ability to use theoretical knowledge in practice.

Educational and methodological support and equipment: multimedia equipment, computer.

Type of activity– communication of new knowledge.

Type of activity– lecture – conversation (using technical means, presentations, chemical experiments).

Teaching methods:

1. According to the sources of transmission and the nature of perception of information -

visual (demonstration of presentation).

2. The nature of cognitive activity is explanatory and illustrative.

Interdisciplinary connections physics.

Progress of the lesson.

Organizational moment.

Learning new material:

1. General information about coarse systems.

2. Characteristics of emulsions.

Fixing the material

Discussion of material on issues.

Homework:

General information about coarse systems.

Systems in which the particle size of the dispersed phase is at least 10~5 cm are called coarsely dispersed. These include emulsions, foams, powders and suspensions, which have a lower degree of dispersion than colloids. In a number of properties, coarsely dispersed systems are close to microheterogeneous systems, and therefore have much in common with colloids.

Like colloids, they are heterogeneous and have a highly developed phase interface. The presence of a significant specific surface area, according to the second law of thermodynamics, leads these systems to aggregative instability. Therefore, aggregative stability can be imparted to such systems by adding a stabilizer, which is adsorbed on particles of the dispersed phase.

Due to the absence of Brownian motion, emulsions, foams and suspensions are kinetically unstable. In them, either settling of particles under the influence of gravity is observed (when the density of the substance of the particles is greater than the density of the medium), or floating of particles (if the density of the substance of the particles is less than the density of the medium).

Coarsely dispersed systems are widespread in nature and are used in practical human activities. They are especially important in food preparation technology, since most culinary products or semi-finished products are emulsions, powders, foams or suspensions.

Characteristics of emulsions.

Structure and production of emulsion. Emulsions are heterogeneous systems of mutually insoluble liquids. In such systems, one of the liquids (dispersed phase) is suspended in another (dispersion medium) in the form of droplets.

Most often, emulsions consist of water and a second liquid, which is usually referred to as “oil.” Thus, “oils” include gasoline, kerosene, benzene, mineral oils, animal, vegetable and other non-polar liquids.

You can disperse the hydrophobic liquid in water, for example by preparing an emulsion of benzene in water. It is quite possible to disperse water in benzene and thereby obtain an emulsion of water in benzene. Therefore, in principle there can be two types of emulsions: oil in water (abbreviated o/w), where the dispersed phase is oil and the dispersion medium is water, and water in oil (abbreviated w/o), when the dispersed phase is water, dispersion medium - oil. An example of an emulsion of the first type is cow's milk (an emulsion of fat in a protein hydrosol), and an example of an emulsion of the second type is natural oil, various medical ointments (emulsions of water in oil).

Emulsions are usually prepared by mechanically dispersing (emulsifying) one liquid into another.

Emulsifiable liquids are vigorously mixed, shaken or subjected to vibration using stirrers, colloid mills, and ultrasound. In culinary practice, this is done using special beaters or sometimes manually with various beaters.

Due to the enormous increase in the interface between the two liquids, the emulsion acquires a large supply of free surface energy E and becomes thermodynamically unstable. According to the second law of thermodynamics, such a system will tend to spontaneously transition to a stable state by reducing the supply of free surface energy. This spontaneous process can occur either due to a decrease in surface tension σ, or due to a decrease in the surface area S, since free surface energy is related to surface tension and the total surface area by the equation E=σS.

If a decrease in the supply of free surface energy occurs due to a decrease in the total surface of the system, this will be expressed in the merging of fat droplets, in a decrease in the number of fat droplets. The fusion of emulsion droplets is called coalescence, she similar to coagulation and quickly ends with the separation of the system into two separate liquid phases with a minimal interface. This merger leads to the destruction of the emulsion. Consequently, like colloids, emulsions are aggregatively unstable systems.

A decrease in the surface energy of the emulsion can be achieved by reducing the surface tension. This can be achieved by introducing into the system any surfactant that can be adsorbed on the surface of emulsion droplets and prevent their merging. Such substances that stabilize the emulsion are called stabilizers or emulsifiers . In this case, the total surface of the system remains unchanged, and the resulting emulsion becomes aggregatively stable.

Dilute emulsions include systems in which the volume fraction of the dispersed phase is less than 1%. They are stable without special emulsifiers. The stability of dilute emulsions is explained by the rather small size of liquid droplets and the insignificant concentration of these systems.

IN concentrated emulsions volume fraction of dispersed phase from 1 to 74%. An increase in concentration leads to a decrease in aggregative stability, because the probability of collision increases, and consequently, the coalescence of droplets. Therefore, to increase the aggregative stability of concentrated emulsions, an emulsifier is introduced, which, being adsorbed at the interface between two liquids, reduces surface tension. Strong adsorption films formed on the surface of emulsified liquid droplets prevent coalescence. The system becomes aggregatively stable. Depending on the type of emulsion, hydrophilic or hydrophobic emulsifiers of varying degrees of dispersion should be used.

Emulsifier must be similar to the liquid that forms the dispersion medium. Thus, o/w emulsions are stabilized by water-soluble high-molecular compounds, for example, proteins or water-soluble hydrophilic soaps (sodium oleate and alkali metal soaps in general). Emulsifiers when preparing a w/o emulsion are high-molecular substances that are insoluble in water, but highly soluble in hydrocarbons (rubber, resins, etc.), as well as polyvalent metal soaps that are insoluble in water.

In adsorption layers, emulsifier molecules containing polar and nonpolar groups (soaps, proteins) are oriented with their polar ends toward the polar liquid and their nonpolar ends toward the nonpolar liquid. On the surface of liquid droplets in o/w and w/o emulsions, the opposite orientation of the molecules of such emulsifiers will be observed.

Such shells of surfactants on the surface of emulsion droplets are quite strong and elastic. When particles collide, they, as a rule, are not destroyed - the emulsions become stable.

In addition to high-molecular compounds and soaps, powders, so-called solid emulsifiers, can serve as emulsifiers for emulsions of both the first and second types. However, they are less effective than soaps and high polymers. Powders must be highly dispersed and must be better wetted by the liquid that serves as the dispersion medium; in this case, most of the solid particles will be on the outer, outer side of the droplets, forming shells of high strength that protect them from coalescence during collisions. If the powder particles are better wetted by the liquid, which is a dispersed phase, then most of each particle will be drawn inside the droplets, the surface of the emulsion droplets will be unprotected, and such emulsions will coalesce. Therefore, hydrophilic powders, such as flour, chalk, iron (III) oxide, clay, stabilize o/w emulsions, while carbon black and other hydrophobic powders stabilize w/o emulsions.

Highly concentrated emulsions with a dispersed phase concentration of more than 74% called gelatinized . In such emulsions, droplets of the dispersed phase are highly deformed. From balls they turn into polyhedra, the latter can be more densely packed. Therefore, highly concentrated emulsions can contain a dispersed phase of up to 99% . The dispersion medium in such emulsions turns into thin films that separate the dispersed phase into polyhedra. Gelatinated emulsions are solid, retain their shape, and do not spread. Examples include butter, margarine, mayonnaise, and thick creams.

Destruction of emulsions. In many cases, the breakdown of the emulsion is demulsification - may be as important as their education. Demulsification comes down to coalescence of the emulsion, i.e., its separation into free liquid phases. Breaking emulsions can be achieved in the following ways:

1) chemical destruction protective films with appropriate substances, for example, the destruction of milk emulsifier by sulfuric acid when determining its fat content;

2) destruction of protective films by mechanical action, for example, when churning sour cream and cream to obtain butter (here de-emulsification is accompanied by concentration, i.e. the formation of a gelatinized emulsion);

3) thermal destruction - separation of emulsions when heated; at the same time, the adsorption of the emulsifier decreases and the number of droplet collisions increases, which leads to their merging. Such destruction (stratification) of emulsions is observed during prolonged boiling of sauces and during the production of ghee. The destruction of emulsions also occurs when the temperature drops - freezing. For example, when mayonnaise is stored below -15° C, the dispersion medium freezes, which upon subsequent thawing leads to its destruction.

The importance of emulsions. Emulsions are widely distributed in nature (crude oil, milky sap of rubber plants). Emulsions are used and formed in many manufacturing processes. A variety of food products are emulsions; milk, butter, margarine, cream.

Milk is a polydisperse system, the components of which are in varying degrees of dispersion. In warm milk, the fat is in an emulsified state, and the protein substances and some of the salts are in a colloidal state, and the other part of the salts are in the form of true solutions. When milk sits, a layer of concentrated emulsion forms - cream. To increase stability, it is homogenized. During the homogenization process, large fat droplets of milk are reduced several times. This homogenized milk is very stable and does not form a layer of cream for several months.

Butter and margarine are made from milk. Margarine is a w/o emulsion, and butter is a complex structured emulsion containing elements of both types of o/w and w/o emulsions in different proportions.

The importance of emulsions and emulsification in culinary practice is great. The physiology of nutrition poses the task of cooking technology not only to increase the digestibility of food, but also to reduce the energy costs for its absorption and facilitate the course of biochemical reactions in the digestive tract. From this point of view, for example, the emulsification of fats in culinary practice is of great importance. As an example, let's look at the features of preparing mayonnaise.

The dispersion medium in these emulsions is water of yolks and vinegar, the dispersed phase is vegetable oil. Emulsifiers include lecithin and vittelin in the yolk and mustard powder proteins. Mayonnaise contains 75% fat. It is crushed into tiny balls. When whipped by hand, their size is 1.5-2 10 -3 cm, and when whipped by machine - from 10 -4 to 4 10 -4. 1 g of sauce contains up to 1 10 12 fat globules. It takes a lot of work to break down the fat this way. If fat were included in food unemulsified, then this work would have to be performed by the human body. In addition, if the surface of 1 cm 3 of oil is only 6 cm 2, then in mayonnaise it reaches 60,000 cm 2. With such an increase in surface area, the reaction between fats and water under the action of enzymes in the digestive tract is greatly facilitated. The smaller the fat globules, the more stable the emulsion is. However, a high degree of fat fragmentation (dispersity) in sauces such as mayonnaise also plays a negative role.

A large surface area leads to an acceleration of the processes of oxidation and rancidity of fats under the influence of light and oxygen. Therefore, mayonnaise must be stored in a dark place and in an airtight container.

It is undesirable to emulsify fat during the cooking of meat broths (usually at high boiling), since emulsified fats are easily hydrolyzed (saponified) and the released fatty acids give the broths the taste of lard and the smell of soap.