What are lipids?
Lipids are a series of organic substances that are part of all living cells. It also includes fats and fat-like substances contained in the cells and tissues of animals as part of adipose tissue, which plays an important physiological role.
The human body itself is able to synthesize all the essential lipids. Only fat-soluble vitamins and essential polyunsaturated fatty acids cannot be synthesized in the body of animals and humans. Basically, lipid synthesis occurs in the liver and epithelial cells of the small intestine. A number of lipids are characteristic of certain organs and tissues, the remaining lipids are present in the cells of all tissues. The amount of lipids contained in organs and tissues is different. Most lipids are found in adipose and nervous tissue.
The lipid content in the human liver varies from 7 to 14% (dry weight). In the case of liver diseases, such as fatty liver, the lipid content in the liver tissue reaches 45%, mainly due to an increase in the amount of triglycerides. Lipids in blood plasma are found in combination with proteins and in this composition they are transported to other organs and tissues.
Lipids perform the following biological functions:
1. Structural. In combination, phospholipids with proteins form biological membranes.
2. Energy. In the process of fat oxidation, a large amount of energy is released, and it is she who goes to the formation of ATP. Most of the energy reserves of the body are stored precisely in the form of lipids, and are consumed in case of a lack of nutrients. So, for example, animals fall into hibernation, and pre-accumulated fats and oils are used to maintain life. Due to the high content of lipids in the seeds of plants, the embryo and seedling develop until they feed on their own. Seeds of plants such as coconut palm, castor bean, sunflower, soybean, rapeseed are the raw material from which vegetable oil is made industrially.
3. Heat-insulating and protective. It is deposited in the subcutaneous tissue and around organs such as the intestines and kidneys. The resulting layer of fat protects the body of the animal and its organs from mechanical damage. Since subcutaneous fat has a low thermal conductivity, it perfectly retains heat, which allows animals to live in cold climates. For whales, for example, this fat helps buoyancy.
4. Lubricating and water repellent. The skin, wool and feathers have a layer of wax that keeps them supple and protects them from moisture. Such a layer of wax is also found on the leaves and fruits of various plants.
5. Regulatory. Sex hormones, testosterone, progesterone and corticosteroids, as well as others, are derivatives of cholesterol. Vitamin D, derivatives of cholesterol, play an important role in calcium and phosphorus metabolism. Bile acids are involved in digestion (emulsification of fats), as well as the absorption of higher carboxylic acids.
Lipids are the source of metabolic water formation. So to get 105 grams of water, you need to oxidize 100 grams of fat. For desert dwellers, such water is vital, for example, for camels, who have to go without water for 10-12 days, such fat is deposited in their hump and used to obtain water. The process of fat oxidation is very important for hibernating animals, such as marmots, bears, etc.
LIPIDS - this is a heterogeneous group of natural compounds, completely or almost completely insoluble in water, but soluble in organic solvents and in each other, giving high molecular weight fatty acids upon hydrolysis.
In a living organism, lipids perform a variety of functions.
Biological functions of lipids:
1) Structural
Structural lipids form complex complexes with proteins and carbohydrates, from which cell membranes and cell structures are built, and participate in various processes occurring in the cell.
2) Spare (energy)
Spare lipids (mainly fats) are the energy reserve of the body and are involved in metabolic processes. In plants, they accumulate mainly in fruits and seeds, in animals and fish - in subcutaneous adipose tissues and tissues surrounding internal organs, as well as liver, brain and nervous tissues. Their content depends on many factors (type, age, nutrition, etc.) and in some cases is 95-97% of all lipids released.
Calorie content of carbohydrates and proteins: ~ 4 kcal / gram.
Calorie content of fat: ~ 9 kcal / gram.
The advantage of fat as an energy reserve, unlike carbohydrates, is hydrophobicity - it is not associated with water. This ensures the compactness of fat reserves - they are stored in an anhydrous form, occupying a small volume. On average, a person has a supply of pure triacylglycerols of approximately 13 kg. These reserves could be enough for 40 days of fasting in conditions of moderate exercise. For comparison: the total glycogen stores in the body are approximately 400 g; during starvation, this amount is not enough even for one day.
3) Protective
Subcutaneous fatty tissues protect animals from cooling, and internal organs from mechanical damage.
The formation of fat reserves in the human body and some animals is considered as an adaptation to an irregular diet and to living in a cold environment. A particularly large supply of fat is in animals falling into long hibernation (bears, marmots) and adapted to living in cold conditions (walruses, seals). The fetus has practically no fat, and appears only before birth.
A special group in terms of their functions in a living organism is made up of protective plant lipids - waxes and their derivatives, covering the surface of leaves, seeds and fruits.
4) An important component of food raw materials
Lipids are an important component of food, largely determining its nutritional value and palatability. The role of lipids in various processes of food technology is exceptionally great. Damage to grain and products of its processing during storage (rancidity) is primarily associated with a change in its lipid complex. Lipids isolated from a number of plants and animals are the main raw materials for obtaining the most important food and technical products (vegetable oil, animal fats, including butter, margarine, glycerin, fatty acids, etc.).
2 Lipid classification
There is no generally accepted classification of lipids.
It is most expedient to classify lipids depending on their chemical nature, biological functions, and also in relation to some reagents, for example, alkalis.
According to their chemical composition, lipids are usually divided into two groups: simple and complex.
Simple lipids - Esters of fatty acids and alcohols. These include fats , waxes And steroids .
Fats - esters of glycerol and higher fatty acids.
Waxes - esters of higher alcohols of the aliphatic series (with a long carbohydrate chain of 16-30 C atoms) and higher fatty acids.
Steroids - esters of polycyclic alcohols and higher fatty acids.
Complex lipids - in addition to fatty acids and alcohols, they contain other components of various chemical nature. These include phospholipids and glycolipids .
Phospholipids - these are complex lipids in which one of the alcohol groups is associated not with fatty acids, but with phosphoric acid (phosphoric acid can be combined with an additional compound). Depending on which alcohol is included in the composition of phospholipids, they are divided into glycerophospholipids (containing glycerol alcohol) and sphingophospholipids (containing sphingosine alcohol).
Glycolipids - these are complex lipids in which one of the alcohol groups is associated not with fatty acids, but with a carbohydrate component. Depending on which carbohydrate component is included in the composition of glycolipids, they are divided into cerebrosides (they contain any monosaccharide, disaccharide or a small neutral homooligosaccharide as a carbohydrate component) and gangliosides (they contain acidic heterooligosaccharide as a carbohydrate component).
Sometimes in an independent group of lipids ( minor lipids ) secrete fat-soluble pigments, sterols, fat-soluble vitamins. Some of these compounds can be classified as simple (neutral) lipids, while others are complex.
According to another classification, lipids, depending on their relationship to alkalis, are divided into two large groups: saponifiable and unsaponifiable.. The group of saponifiable lipids includes simple and complex lipids, which, when interacting with alkalis, are hydrolyzed to form salts of macromolecular acids, called "soaps". The group of unsaponifiable lipids includes compounds that are not subject to alkaline hydrolysis (sterols, fat-soluble vitamins, ethers, etc.).
According to their functions in a living organism, lipids are divided into structural, reserve and protective.
Structural lipids are mainly phospholipids.
Spare lipids are mainly fats.
Protective lipids of plants - waxes and their derivatives, covering the surface of leaves, seeds and fruits, animals - fats.
FATS
The chemical name for fats is acylglycerols. These are esters of glycerol and higher fatty acids. "Acyl-" means "fatty acid residue".
Depending on the number of acyl radicals, fats are divided into mono-, di- and triglycerides. If the molecule contains 1 fatty acid radical, then the fat is called MONOACYLGLYCEROL. If there are 2 fatty acid radicals in the molecule, then the fat is called DIACYLGLYCERIN. Triacylglycerols predominate in humans and animals (they contain three fatty acid radicals).
The three hydroxyls of glycerol can be esterified either with just one acid, such as palmitic or oleic, or with two or three different acids:
Natural fats contain mainly mixed triglycerides, including residues of various acids.
Since the alcohol in all natural fats is the same - glycerol, the differences observed between fats are due solely to the composition of fatty acids.
Over four hundred carboxylic acids of various structures have been found in fats. However, most of them are present only in small quantities.
The acids contained in natural fats are monocarboxylic, built from unbranched carbon chains containing an even number of carbon atoms. Acids containing an odd number of carbon atoms, having a branched carbon chain, or containing cyclic fragments are present in minor amounts. The exceptions are isovaleric acid and a number of cyclic acids found in some very rare fats.
The most common fatty acids contain between 12 and 18 carbon atoms and are often referred to as fatty acids. The composition of many fats includes low molecular weight acids (C 2 -C 10) in a small amount. Acids with more than 24 carbon atoms are present in waxes.
The glycerides of the most common fats contain a significant amount of unsaturated acids containing 1-3 double bonds: oleic, linoleic and linolenic. Animal fats contain arachidonic acid containing four double bonds; acids with five, six or more double bonds have been found in fish and marine animal fats. Most unsaturated lipid acids have a cis-configuration, their double bonds are isolated or separated by a methylene (-CH 2 -) group.
Of all the unsaturated acids found in natural fats, oleic acid is the most common. In very many fats, oleic acid makes up more than half of the total mass of acids, and only a few fats contain less than 10%. Two other unsaturated acids - linoleic and linolenic - are also very widespread, although they are present in much smaller quantities than oleic acid. Significant amounts of linoleic and linolenic acids are found in vegetable oils; for animal organisms, they are essential acids.
Of the saturated acids, palmitic acid is almost as widespread as oleic acid. It is present in all fats, with some containing 15-50% of the total acid content. Stearic and myristic acids are widely distributed. Stearic acid is found in large quantities (25% or more) only in the reserve fats of some mammals (for example, in sheep fat) and in the fats of some tropical plants, for example, in cocoa butter.
It is advisable to divide the acids contained in fats into two categories: major and minor acids. The main acids of fat are considered to be acids, the content of which in fat exceeds 10%.
Physical properties of fats
As a rule, fats do not withstand distillation and decompose, even if they are distilled under reduced pressure.
The melting point, and, accordingly, the consistency of fats depend on the structure of the acids that make up their composition. Solid fats, i.e., fats that melt at a relatively high temperature, consist mainly of glycerides of saturated acids (stearic, palmitic), and oils that melt at a lower temperature and are thick liquids contain significant amounts of glycerides of unsaturated acids (oleic , linoleic, linolenic).
Since natural fats are complex mixtures of mixed glycerides, they do not melt at a certain temperature, but in a certain temperature range, and they are first softened. To characterize fats, it is usually used solidification temperature, which does not coincide with the melting point - it is somewhat lower. Some natural fats are solids; others are liquids (oils). The solidification temperature varies widely: -27 ° C for linseed oil, -18 ° C for sunflower oil, 19-24 ° C for cow fat and 30-38 ° C for beef fat.
The solidification temperature of fat is determined by the nature of its constituent acids: it is the higher, the greater the content of saturated acids.
Fats dissolve in ether, polyhalogen derivatives, carbon disulfide, aromatic hydrocarbons (benzene, toluene) and gasoline. Solid fats are hardly soluble in petroleum ether; insoluble in cold alcohol. Fats are insoluble in water, but they can form emulsions which are stabilized in the presence of surfactants (emulsifiers) such as proteins, soaps and some sulfonic acids, especially in slightly alkaline media. Milk is a natural emulsion of fat stabilized by proteins.
Chemical properties of fats
Fats enter into all chemical reactions characteristic of esters, however, in their chemical behavior there are a number of features associated with the structure of fatty acids and glycerol.
Among the chemical reactions involving fats, several types of transformations are distinguished.
Chapter II. LIPIDS
§ 4. CLASSIFICATION AND FUNCTIONS OF LIPIDS
Lipids are a heterogeneous group of chemical compounds that are insoluble in water, but highly soluble in non-polar organic solvents: chloroform, ether, acetone, benzene, etc., i.e. their common property is hydrophobicity (hydro - water, phobia - fear). Due to the wide variety of lipids, it is impossible to give a more precise definition of them. Lipids in most cases are esters of fatty acids and some kind of alcohol. The following classes of lipids are distinguished: triacylglycerols, or fats, phospholipids, glycolipids, steroids, waxes, terpenes. There are two categories of lipids - saponifiable and unsaponifiable. Saponifiables include substances containing an ester bond (waxes, triacylglycerols, phospholipids, etc.). Unsaponifiables include steroids and terpenes.
Triacylglycerols or fats
Triacylglycerols are esters of the trihydric alcohol glycerol
and fatty (higher carboxylic) acids. The general formula of fatty acids is: R-COOH, where R is a hydrocarbon radical. Natural fatty acids contain from 4 to 24 carbon atoms. As an example, we give the formula of one of the most common stearic acid in fats:
CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -COOH
In general, the triacylglycerol molecule can be written as follows:
If triacyoglycerol contains residues of various acids (R 1 R 2 R 3), then the central carbon atom in the glycerol residue becomes chiral.
Triacylglycerols are non-polar and therefore practically insoluble in water. The main function of triacylglycerols is energy storage. When 1 g fat is oxidized, 39 kJ of energy is released. Triacylglycerols accumulate in adipose tissue, which, in addition to storing fat, performs a thermal insulating function and protects organs from mechanical damage. For more information on fats and fatty acids, see the next paragraph.
Interesting to know! The fat with which the camel's hump is filled is, first of all, not a source of energy, but a source of water formed during its oxidation.
Phospholipids
Phospholipids contain hydrophobic and hydrophilic regions and therefore have amphiphilic properties, i.e. they are able to dissolve in non-polar solvents and form stable emulsions with water.
Phospholipids, depending on the presence of glycerol and sphingosine alcohols in their composition, are divided into glycerophospholipids And sphingophospholipids.
Glycerophospholipids
The structure of the glycerophospholipid molecule is based on phosphatidic acid, formed by glycerol, two fatty acids and phosphoric acids:
In glycerophospholipid molecules, an HO-containing polar molecule is attached to phosphatidic acid by an ester bond. The formula of glycerophospholipids can be represented as follows:
where X is the residue of an HO-containing polar molecule (polar group). The names of phospholipids are formed depending on the presence of one or another polar group in their composition. Glycerophospholipids containing an ethanolamine residue as a polar group,
HO-CH 2 -CH 2 -NH 2
are called phosphatidylethanolamines, a choline residue
- phosphatidylcholines, serine
- phosphatidylserines.
The formula for phosphatidylethanolamine looks like this:
Glycerophospholipids differ from each other not only in polar groups, but also in fatty acid residues. They include both saturated (usually consisting of 16-18 carbon atoms) and unsaturated (more often containing 16-18 carbon atoms and 1-4 double bonds) fatty acids.
Sphingophospholipids
Sphingophospholipids are similar in composition to glycerophospholipids, but instead of glycerol they contain the amino alcohol sphingosine:
or dihydrosphingazine:
The most common sphingophospholipids are sphingomyelins. They are formed by sphingosine, choline, fatty acid and phosphoric acid:
The molecules of both glycerophospholipids and sphingophospholipids consist of a polar head (formed by phosphoric acid and a polar group) and two non-polar hydrocarbon tails (Fig. 1). In glycerophospholipids, both non-polar tails are fatty acid radicals, in sphingophospholipids, one tail is a fatty acid radical, the other is a hydrocarbon chain of sphingazine alcohol.
Rice. 1. Schematic representation of a phospholipid molecule.
When shaken in water, phospholipids spontaneously form micelles, in which nonpolar tails are collected inside the particle, and polar heads are located on its surface, interacting with water molecules (Fig. 2a). Phospholipids can also form bilayers(Fig. 2b) and liposomes– closed bubbles surrounded by a continuous bilayer (Fig. 2c).
Rice. 2. Structures formed by phospholipids.
The ability of phospholipids to form a bilayer underlies the formation of cell membranes.
Glycolipids
Glycolipids contain a carbohydrate component in their composition. These include glycosphingolipids containing, in addition to carbohydrates, alcohol, sphingosine and a fatty acid residue:
They, like phospholipids, consist of a polar head and two non-polar tails. Glycolipids are located on the outer layer of the membrane, are an integral part of the receptors, and provide cell interaction. They are especially numerous in the nervous tissue.
Steroids
Steroids are derivatives cyclopentanperhydrophenanthrene(Fig. 3). One of the most important representatives of steroids - cholesterol. In the body, it occurs both in the free state and in the bound state, forming esters with fatty acids (Fig. 3). In free form, cholesterol is part of the membranes and lipoproteins of the blood. Cholesterol esters are its reserve form. Cholesterol is the precursor of all other steroids: sex hormones (testosterone, estradiol, etc.), hormones of the adrenal cortex (corticosterone, etc.), bile acids (deoxycholic, etc.), vitamin D (Fig. 3).
Interesting to know! The body of an adult contains about 140 g of cholesterol, most of which is found in the nervous tissue and adrenal glands. Every day, 0.3-0.5 g of cholesterol enters the human body, and up to 1 g is synthesized.
Wax
Waxes are esters of long-chain fatty acids (14-36 carbons) and long-chain monohydric alcohols (16-22 carbons). As an example, consider the formula for wax formed by oleic alcohol and oleic acid:
Waxes perform mainly a protective function, being on the surface of leaves, stems, fruits, seeds, they protect tissues from drying out and penetration of microbes. They cover the wool and feathers of animals and birds, protecting them from getting wet. Beeswax serves as a building material for bees to create honeycombs. In plankton, wax is the main form of energy storage.
Terpenes
Terpene compounds are based on isoprene residues:
Terpenes include essential oils, resin acids, rubber, carotenes, vitamin A, and squalene. As an example, here is the formula for squalene:
Squalene is the main component of the secretion of the sebaceous glands.
The role of lipids in the life processes of the body is diverse.
Structural. In combination with proteins, lipids are structural components of all biological cell membranes, and therefore affect their permeability, participate in the transmission of a nerve impulse in the creation of intercellular interaction.
Energy. Lipids are the most energy intensive cellular fuel. When oxidizing 1 g of fat, 39 kJ of energy is released, which is twice as much as when oxidizing 1 g of carbohydrates.
Reserve. Lipids are the most compact form of energy storage in the cell. The fat content in the body of an adult is from 6 to 10 kg.
Protective. Possessing pronounced thermal insulation properties, lipids protect the body from thermal effects, the fat pad protects the body and organs of animals from mechanical and physical damage; protective membranes in plants (wax coating on leaves and fruits) protect against infections and excessively intensive water exchange.
Regulatory. Some lipids are precursors of vitamins, hormones, secondary metabolites - prostaglandins, leukotrienes, thromboxanes. In bacteria, lipids determine the taxonomic individuality, the type of pathogenesis, and many other features. Violation of lipid metabolism in humans leads to the development of such pathological conditions as atherosclerosis, obesity, cholelithiasis.
Classification of lipids. Lipids are chemically heterogeneous substances. In this regard, there are different approaches to their classification. But first of all, they are divided into simple and complex.
Simple (neutral) lipids primarily include derivatives of higher fatty acids and alcohols - icylglycerolipids, waxes, cholesterol esters, glycolipids and other similar compounds. Their molecules do not contain nitrogen, phosphorus and sulfur atoms.
As another defining feature, the nature of the link connecting the hydrophilic and hydrophobic regions of the molecule is used. Such a link is usually polyhydric aliphotic alcohols containing two or hydroxyl groups or complex lipids connected to another residue contain a heteroatom, these include phospholipids, glycolipids, steroids.
Simple lipids can be divided into neutral and polar.
Neutral lipids 95-96% are acylglycerols and, in fact, they are called fats.
In polar glycerolipids, the third hydroxyl group is either free (two OH groups may also be free - these are diacyl or monoacylglycerols). In polar glycerolipids, the third hydroxyl group can also be attached to the hydrophilic head.
The residues are fatty acids. The structural diversity of lipids is mainly due to the variety of fatty acids included in them, which differ in the degree and nature of the branching of the carbon chain, the number and position of the double bond, the nature and number of other functional groups, and finally in the length of the carbon chain. Fatty acids that are part of the lipids of higher plants and animals, as a rule, have an even number of carbon atoms, and acids with 16-20 carbon atoms per molecule are predominant.
The simplest representatives of natural fatty acids include saturated acids with a length of unbranched hydrocarbon chain of the general formula.
CH 3 (CH 2) and COOH, their main representatives are shown in the table.
Most common natural fatty acids
| Code Designation * | Structure | Systematic name | Trivial name |
| From 12:0 From 14:0 From 16:0 From 18:0 From 20:0 From 22:0 From 24:0 From 14:1 From 16:1 From 18:1 From 18:1 From 18:1 From 18 :1 from 22:1 from 18:2 from 18:3 from 20:3 from 20:4 | CH 3 (CH 2) 10 COOH CH 3 (CH 2) 12 COOH CH 3 (CH 2) 14 COOH CH 3 (CH 2) 16 COOH CH 3 (CH 2) 18 COOH CH 3 (CH 2) 20 COOH CH 3 (CH 2) 22 COOH CH 3 (CH 2) 3 CH \u003d CH (CH 2) 7 COOH CH 3 (CH 2) 5 CH \u003d CH (CH 2) 7 COOH CH 3 (CH 2) 7 CH \u003d CH (CH 2) 7 COOH CH 3 (CH 2) 5 CH \u003d CH (CH 2) 9 COOH CH 3 (CH 2) 5 CH \u003d CH (CH 2) 9 COOH CH 3 (CH 2) 10 CH \u003d CH (CH 2) 4 COOH CH 3 (CH 2) 7 CH \u003d CH (CH 2) 11 COOH CH 3 (CH 2) 4 (CH \u003d CHCH 2) 2 (CH 2) 6 COOH CH 3 CH 2 (CH \u003d CHCH 2) 3 ( CH 2) 6 COOH CH 3 (CH 2) 4 (CH=CHCH 2) 3 (CH 2) 5 COOH CH 3 (CH 2) 4 (CH=CHCH 2) 4 (CH 2) 2 COOH | Saturated n-Dodecane n-Tetradecanoic n-hexadecanoic n-Octadecanoic n-Eicosanoic n-Docosan n-Tetracosane Monoenoic cis-Tetradecene-9-ovaya cis-Hexadecene-9-ovaya cis-Octadecene-9-ovaya cis-Octadecene-11th trance-Octadecene-11th cis-Octadecene-6-ova cis-Docosene-13-ova Polyene cis, cis-Octadecadien-9,12-ova cis, cis, cis-Octadecatriene-9, 12, 15-ova cis, cis, cis-Eicosatriene-8,11,14-ova cis, cis, cis, cis-Eicosatetraen-5,8,11,14-ova | Lauric Myristic Palmitic Stearic Arachinic Behenic Lignoceric Myristoleic Palmitoleic Oleic Vaccene Trans-Vaccene Petroceline Eruic Linoleic Linolenic Dihomo-γ-linoleic Arachidonic |
* Numbers indicate the number of carbon atoms and double bonds in the chain
Among them, palmitic acid (C 16:0) occupies a special position, it can be synthesized by all organisms, which is the primary product formed under the action of fatty acid synthetase, and the starting material for the biosynthesis of other acids of the group - stearic, lauric, myristic, etc.
The biosynthesis of fatty acids, both saturated and unsaturated, occurs due to chain elongation by two CH 2 groups under the action of ELON gas enzymes.
Higher plants are characterized mainly by C 18 -unsaturated acids, biosynthetically obtained from C 18:0 stearic acid under the action of the desaturase enzyme.
In mammals and a number of bacteria, palmitic and stearic
acids serve as precursors for two widely used
nyh monoenoic (monounsaturated) fatty acids - palmitic and oleic. Almost all natural monoenoic acids are cis-isomers
CH 3 (CH 2) m CH \u003d CH (CH 2) n COOH general formula of monoenoic fatty acids
Mammalian fats and plant lipids contain a significant amount of polyene fatty acids. All natural polyenoic acids are non-conjugated: cis-double bonds in their hydrocarbon chains are separated, as a rule, by one methylene group. As a result, one or more repeating groups are formed in acid molecules.
-CH \u003d CH-CH 2 -CH \u003d CH-, therefore they are called acids of the divinylmethane series, they are represented by the general formula
Linoleic (n=2) and linolenic (n=3) acids are not synthesized in the body of higher animals and humans, but come from food, they are often called essential or essential fatty acids. Arachidonic and dihomo-γ-linoleic acids are precursors in the biosynthesis of prostaglandins and leukotrienes.
Along with straight-chain saturated and unsaturated acids, branched-chain fatty acids occur naturally. In particular, these include the most widely distributed natural tuberculostearic acid, first isolated from tubercle bacillus
Fatty acids containing a cyclopropane ring have been found in some plants and bacteria, such as lactobacillus and strechulic. The biosynthesis of such acids occurs by transferring the methylene group from S-adenosylmethionine to the double bond of monoenoic acid
Natural lipids also contain hydroxy acids, which are part of the lipids of bacterial cells. For example, 2(3)-hydrocystearic, 2(3)-hydroxypalmethic, 2-hydroxylignoceric, ricinoleic
Studies of the composition of lipids and their fatty acid composition, depending on the growing conditions of their sources, have shown that hydroxy acids accumulate in significant amounts of a stressful situation (frost, dry years, etc.)
Acylglycerides can be simple - formed by only one acid and complex or mixed, when they include residues of various acids. In addition, the functional groups in triacylglycerides can be differently oriented in space. These different orientations are in the form of a fork, a chair, a rod.
Pure acylglycerins are colorless, tasteless and odorless substances. The color, smell and taste of fats are determined by the presence of specific impurities in them. The melting and freezing points of acylglycerols do not match. This may be due to supercooling or the existence of several crystalline modifications. melting point of triacylglycerols containing residues trance-unsaturated acids is higher than that of acylglycerols containing residues cis-unsaturated fatty acids with the same number of carbon atoms.
In addition to being used for their intended purpose as fats, triglycerides can serve as a source for individual or near-individual components, such as the production of cotton palmetin as a result of demargarization. Isolation is based on sacristies in the melting and boiling points of not only saturated and unsaturated triglycerides, but also cis- And trance-isomers of unsaturated glycerides.
Waxes are fat-like substances that are solid at room temperature. The composition of the wax includes esters of fatty acids and higher monohydric (less often - dihydric) alcohols, and acids and alcohols mostly contain an even number of carbon atoms (C 13 -C 36). In addition, waxes always contain free acids, and often carbohydrates, and contain sterols and colorants as co-compounds.
Waxes are divided into vegetable and animal. In plants, waxes are mainly contained in the outer layer and play a mainly protective role. Covering the stems, fruits and plants with a thin layer of leaves, wax coating protects plants from damage, pests, and water loss slows down. Vegetable waxes include palm leaf wax (carnauba wax), flax stem wax, and industrial candeilla wax.
Animal waxes include spermaceti, it is isolated from spermaceti oil contained in the cranial cavity of the sperm whale. Cetyl ester of palmitic acid C 15 H 31 COOC 16 H 33 predominates in spermaceti.
Beeswax contains C 24 -C 34 alcohols esterified with higher acids (palmitic C 15 H 31 COOH, cerotinic C 25 H 51 COOH).
Chinese wax secreted by insects mainly consists of ceryl ester of cerotinic acid (C 25 H 51 COOC 26 H 53).
Compared to glycerides, wax esters are more difficult to saponify and are less soluble in common fat solvents.
Waxes find a variety of applications as additives to creams, ointments, lipsticks, are used in the manufacture of candles, soaps, plasters, shampoos. For example carnauba wax.
The composition of waxes varies from plant to plant. A unique wax was found in the fruits and seeds of Californian simongia (jojoba). This wax is liquid. Its Indians ate it and used its medicinal properties (wound healing, etc.). Its peculiarity is that it acts as a reserve nutrient used during seed germination. Without triacyl glycerides in its composition, this wax does not burn and does not decompose like ordinary oil. This makes it possible to use it for lubrication of high-speed motors, which lengthens their operation time by 5-6 times. The hardy jojoba shrub is unpretentious, grows on poor and saline soils, and its fruits and seeds contain up to 50% liquid wax.
Fat-like substances include cutin and suberin.
Cutin covers the top of the epidermis with a thin layer……………..
tissues from drying out and penetration of microorganisms. It consists of C 16 and C 18 ω-hydroxycarboxylic acids linked to each other by ester bonds into a polymer network.
Suberin is a polymer that impregnates the cell walls of the primary root cortex. This makes the cell walls strong and impermeable to water and gases, which increases the protective properties of the integumentary tissue. Suberin is similar to Cutin, but in addition to hydroxy acids, it includes dicarboxylic acids and dihydric alcohols.
Glycolipids. The term refers to a diverse and extensive group of lipids in which the hydrophobic portion of the lipid molecule is linked to a hydrophilic polar head composed of one or more carbohydrate residues. As the main carbohydrate components in the composition of glycolipids, glucose and galactose or their sulfated derivatives (usually galactosyl sulfate), amino sugars (galactosalin and glucosalin) or their acetyl derivatives are most often found. Glyceroglycolipids are present in nature mainly as glycosyldiacil glycerols.
Lecture #2
complex lipids.
Glycerophospholipids A common structural fragment of all glycerophospholipids is phospholipid acid (1,2-diacyl-3-phosphoglycerol)
Phosphatidic acid is formed in the body during the biosynthesis of triacylglycerides and glycerophospholipids as a common intermediate metabolite. All natural glycerophospholipids belong to the L-series and have one asymmetric atom. The composition of fatty acids of various glycerophospholipids differs even within the same organism, which determines the specificity of phospholipids.
Phospholipids are essential components of most membranes in animal, plant, and bacterial cells.
Depending on the HOR substituents, various groups of phospholipids are distinguished
| Name of glycerophospholipid | HOR group | |
| Trivial name | Structure | |
| Nitrogen Free |  |
|
| Phosphatylglyceride | glycerol | |
| Phosphatidylglyceride | cardiolipin |  |
| Phosphatidylinositol | inositol |  |
| containing nitrogen |  |
|
| Phosphatidylethanolamine | cephalin | |
| Phosphatidylcholine | choline (lecithin) |  |
| Phosphatidylserine | serine |  |
Lecithin in its composition contains an amino alcohol in the form of trimethylammonium salt. Depending on which carbon atom is associated with phosphoric acid, its α and β forms are distinguished
α-lecithin β-lecithin
Lecithin found in cells, especially in the brain tissues of humans and animals, in plants it is mainly in soybeans, sunflower seeds, wheat germ. In bacteria, its content is extremely low.
Cephalin is also found in the cell membranes of higher plants and animals.
In addition to phospholipids belonging to the class of diacylglycerides, many natural objects contain small amounts of monoacylglycerides, called lysophospholipids.
x - residues of choline, ethanolamine, serine
Glycerophospholipids with cyclic polyhydroxy derivatives and a free OH group are present in the brain of mammals and in the membranes of nerve cells.
They are formed by hydrolysis in the phosphatidiadichon bond in the second position under the action of a specific enzyme, phospholipase A 2 . Lysophospholipids form a strong hemolytic effect.
lysophospholipids
Plasmalogens. They differ from the above glycerophospholipids in that instead of an acid residue at the first carbon atom, they contain α, β-unsaturated alcohol linked by an ether bond to the OH group……………
Hydrolysis of this group produces aldehydes, hence the name phosphatidals. Plasmalogens account for up to 10% of brain and muscle tissue phospholipids.
an example of a plasmalogen
(phosphatidolethanolamine)
They are also found in erythrocytes (up to 25%), are part of bacterial membranes, but are practically not found in plants. The hydrogenated analogue is called trangocyte. It speeds up aggregation.
Cardiolipin is practically localized in listochondria and plays an important role in the structural organization and functioning of the respiratory complexes.
Among glycoglycerolipids, a small group of phosphorus-containing glycolipids, found mainly in bacterial cells, has been found. For example
The residues of glycerophospholipids can contain carbohydrate residues as the alcohol component of H 3 PO 4 .
Complex lipids are also derivatives of sphingosine or its saturated analogue, dihydrophosphingosine.
sphingosine D-sphinganine
(D-i-sfingenin)
Acylation of the NH 2 group of the fatty acid sphingosine produces ceramide, the phosphocholine derivative of which is called sphingomyelin, that is, the OH group may contain an H 3 PO 4 residue.
Sphingolipids are especially rich in the brain and nervous tissues. Sphingomyelins are found in the tissues of the kidneys, liver, and blood lymph.
In general, natural long chain bases (sphingosines) are C 12 -C 22 compounds of two types. Unsaturated molecules with three functional groups (azothacylated representatives) are mainly of animal origin, while their saturated counterparts with four groups are of plant origin:
With a free NH 2 - group - sphingosines with an acylated NH 2 - group - ceramides containing a residue of phosphoric acid and choline - sphingomyelins.
Glycosphingolipids- derivatives of ceramides, the alcohol group of which is glycosylated with the remains of one or more carbohydrates.
Cerebrosides
galactosylceramides
Gangliosides - the carbohydrate part is oligomeric - branched. In this they differ from cerebrosides.
As well as in acylglycerides, the composition of phospholipids isolated from the same raw material is not identical; in plants, depending on the type of culture, it contains from 0.3 to 1.8% of phospholipids.
Ceramides are found in many animal and plant tissues, while swingomyelins are found only in animal cells. Sphingolipids are part of many dosage forms, so their chemical synthesis has been mastered. On the basis of sphingolipids, pharmacological active preparations with an antibacterial agent, cosmetic products have been created that allow protecting against viruses, bacteria and fungi.
Red algae, sea sponges, starfish are used as natural sources of sphingo compounds.
Cerebrosides can be isolated from soybeans, but natural representatives of sphingolipids due to the low content of road objects. And for pharmacological purposes, they are obtained synthetically. Mostly biochemical approaches are used.
Functional properties of lipids
According to their functions in the body, lipids are divided into two main groups - reserve or reserve and structural or protoplasmic.
Spare lipids (mainly acylglycerides) are high-calorie and constitute the body's energy and construction reserve, which it uses during periods of malnutrition and during illness. The high calorie content of fat allows the body in extreme situations to exist at the expense of its reserves for a long time (from several weeks to 1.5 months). Spare lipids are protective substances that help the body (plant or animal) to endure the adverse effects of the external environment, such as low temperatures. The latter is very important for plants, they suffer more from winter and summer temperature fluctuations. In this regard, up to 90% of all plants contain storage lipids. Spare lipids of animals and fish are concentrated in the subcutaneous adipose tissue, protecting the body from injury. Waxes can also be classified as protective lipids. Reserve lipids in most plants and animals are the main group of lipids by mass (95-96%) and are relatively easy to extract from fat-containing material (“free lipids”).
Structural lipids - and this is primarily phospholipids form complex complexes with proteins, carbohydrates and in the form of such supramolecular structures are part of the cell wall and participate in complex processes occurring in the cell. They belong to hard-to-remove bound and strongly bound lipids. To extract them, it is first necessary to destroy their bonds with proteins and carbohydrates.
When lipids are extracted from oilseed raw materials, a large group of substances, pigments, fat-soluble vitamins, and sterols, pass into the oil along with them. All these accompanying substances play an important role in the life of living systems.
Associated substances contained in raw fat
1. Fat-soluble pigments are substances that determine the color of oils and fats, the most common of which are carotenoids and chlorophylls.
Carotenoids are red-yellow plant pigments that provide color to a number of fats, as well as vegetables and fruits, egg yolk and many other products. By their chemical nature, these are hydrocarbons C 40 H 56 - carotenes and their oxygen-containing derivatives. Among them, the most famous is β-carotene (pro-vitamin A)
β-carotene gives color to vegetables, fruits and fruits. In addition to coloring properties, β-carotene is important because it is a precursor of vitamin A. A large amount of β-carotene is found in carrots, corn seeds, and palm oil.
The yellow dye from marigold petals is a fat-soluble dye and is isolated from plants in the form of an oil extract. It is used for coloring fat-soluble products - butter, cheese, etc. in the form of an oil extract.
The carotenoids baxin and norbixin are isolated from the seeds and pulp of the oleander tree (Bixaorellana), they are soluble in vegetable oil and are used as food colorings.
Chlorophyll - the coloring matter of green plants is a complex of magnesium with porphine derivatives.
Chlorophyll consists of blue-green chlorophyll (A) and yellow-green chlorophyll (B) in a ratio of 2: 1………………………
R= CH 3 (chlorophyll)
Chlorophyll gives a green color to many vegetables and fruits - lettuce, green onions, dill. Cotton seeds contain a pigment called gossypol. From 0.14 to 2.5%, gossypol itself and its transformation products color cottonseed oil in a dark yellow or brown color. Gossypol contained in the seeds, leaves, stems of cotton is a toxic substance. Excess gossypol in oil is unacceptable because it is a toxic substance. When unrefined oils are stored and heated, gossypol forms dark products and gives the oil an unpleasant taste. Rapid oxidation occurs. According to its structure, gossypol is a naphthalene dimer containing hydroxyl, aldehyde, methyl and isopropyl substituents:
fat soluble vitamins. These are mainly vitamins of group A (retinol), group D (ergocalciferol - D 2 and cholcalciferol - D 3), tocopherols (vitamin E), vitamins of group K (phylloquinones and menaquinones). Pigments and vitamins will be considered in more detail in the course "Food and Biologically Active Supplements".
Sterols. These unsaponifiable substances are polycyclic alcohols and ethers. The basis of sterols is perhydrocyclopentafenatrene, in the third position of which there is an OH group, in the 17th position there is a substituent R, which varies depending on the type of sterol
etc. R/ - fatty acid residue
OH in the third position, may be esterified with acetic acid or a fatty acid residue.
Sterols are alicyclic substances that are part of the group of steroids, usually they are crystalline monohydric alcohols (sterols) or their esters (sterides).
According to the source of their containing sterols are divided into:
zoosterols - found in animal fats
phytosterols - found in plants
mycosterols - found in mushrooms
The role of sterols is to regulate metabolism in the body, and specifically bile acids, train the immune system, and a number of others, help reduce stress factors such as malnutrition, poor environmental impact, pollution, some of them have anti-inflammatory and antihypoglycemic effects, which is important in the treatment of cardiovascular diseases and diabetes.
Cholesterol is the most important of the animal sterols. On the one hand, it is necessary for the synthesis of steroid hormones, while an excess of it contributes to the deposition in the form of plaques on blood vessels, which makes them brittle. Therefore, its intake with food should be controlled. A cholesterol level of 198-200 mg/di is considered normal. Cholesterol comes both with food 300-500 mg per day, and is formed biosynthetically 500-1000 mg. (70-80% is synthesized in the liver).
Cholesterol is found in the tissues of all animals and is absent, or present in small amounts, in plants.
Ergosterol is the precursor of Vitamin D.
Of the plant sterols, ecdysterone is the most important. It acts as an anabolic on muscle tissue, improves liver and heart function, and improves blood composition. It is taken as a nutritional supplement for athletes.
Processes that occur during the storage of fats.
During storage, fats are unstable and break down relatively quickly. Transformations can proceed along ester groups or along the hydrocarbon skeleton of the molecule.
Hydrolysis of triglycerides
………………
Hydrolysis proceeds stepwise through the intermediate formation of diacyl, monoacyl and then complete hydrolysis to glycerol. Hydrolysis of triacylglycerols is widely used in engineering for the production of fatty acids, glycerol, mono- and diacylglycerols. Hydrolytic decomposition of fats, lipids of grain, flour, cereals and other fat-containing food products is one of the reasons for the deterioration of their quality. This process is especially accelerated if the products are stored in the light, at high humidity, temperature, or other conditions that accelerate aging. The depth of hydrolysis of fats can be characterized by acid number. Acid number - the number of mg KOH required to neutralize the free fatty acids contained in 1 gram of food or fat. The acid number is one of the indicators of product quality and is regulated by the standard.
Interesterification. Of great practical importance are reactions in which there is an exchange of acyl groups (acyl migration) - intermolecular and intramolecular interesterification. Chemically, this process can take place under the influence of various agents. In practice, this process of exchange of acyl groups is important in obtaining fats of a soft consistency in the cross-transesterification of high-melting fats of animal origin and liquid vegetable fats. Plastic margarines are obtained with a melting point of 25-35 0 C. Such fats are very convenient for use in baking, in the manufacture of confectionery, cakes. Alkalis and alcoholates are used as catalysts for the transesterification of fats. When they interact with triacylglycerols, the saponification process first proceeds, sodium or potassium glycerate is formed, which is the actual catalyst for transesterification. The mechanism of transesterification is the same as for monoalcohol ethers.
The mechanism of the transesterification reaction consists in the interaction of the carbonyl group ›C=O of the ester with alcohol groups.
The rate depends on the composition of the fat, the degree of its saponification, temperature, type, quantity and activity of the catalyst.
Reactions of acylglycerols involving a hydrocarbon radical
1. Hydrogenation of acylglycerols. It is carried out under the action of H 2 at elevated temperatures in the presence of a catalyst (most often Ni-Re). For example, the hydrogenation of oils and fats with molecular hydrogen in industry is carried out at temperatures of 180-240 ◦ C in the presence of copper-nickel catalysts, at a pressure close to atmospheric. The task of hydrogenation is to change the fatty acid composition in order to change the consistency and properties of fat. Depending on the complete or partial addition of hydrogen to the unsaturated chain, fats of various consistencies are formed. The main chemical reaction that occurs in this case is the addition of hydrogen with double bonds in the side chains of carboxylic acids included in acylglycerols
The reaction is similar to the hydrogenation of alkenes.
Given the fact that different double bonds interact differently with hydrogen, it is possible to selectively hydrogenate one or another double bond in molecules of unsaturated acylglycerides. So in liquid oils, first one of the double bonds of linoleic acid is hydrogenated to linolenic, then linolenic acid is reduced to oleic, and only then stearic acid is formed during excessive hydrogenation.
By selecting the reaction conditions and appropriate catalysts, the desired fat structure can be achieved.
Lecture #3
Determining the hydrogenation condition and the corresponding catalyst,
you can get the desired structure of fat.
Avoid concomitant processes of isomerization of the location of double bonds and cis-trans- isomerization is possible by selection of catalyst and hydrogenation conditions.
Oxidation of acylglycerides. It is well known that olefins are easily oxidized by the action of atmospheric oxygen at the allyl position at the double bond. Fats that have an unsaturated hydrocarbon chain in the molecule are no exception. The primary products are hydroperoxides of various structures
The resulting hydroperoxides are unstable and can be converted into other products both due to the transformations of the hydroperoxide groups themselves and due to processes initiated by hydroperoxides. In this case, epoxides, alcohols, aldehydes, ketones, acids and their derivatives with hydrocarbon chains of various lengths can be formed.
In addition, autocatalytic oxidation processes with atmospheric oxygen can be accompanied by deeper oxidation with chain breaking, isomerization and polymerization, as a result of which aldehydes, polyenes, ethers and peroxides accumulate.
The direction and depth of oxidation of oils and fats depends primarily on their acyl composition.
With an increase in the degree of unsaturation of fatty acids that make up acylglycerols, the rate of their oxidation increases. For example, the ratio of the rate of oxidation of oleic - linoleic and linoleic acids is 1:27:77. Acylglycerols saturated with atmospheric oxygen do not oxidize under normal conditions. Inhibitors inhibit the oxidation process. They form stable radicals that are not further involved in the oxidation process. These compounds include ionol and other compounds of trisubstituted phenol. Of the natural antioxidants, tocopherol gosipol is of the greatest importance. With the introduction of antioxidants in the amount of 0.01%, the resistance of fats to oxidation increases by 10-15 times.
The activity of oxidants is affected by concomitant substances, so the duration of action of antioxidants increases in the presence of synergists (from the Greek synergos - acting together). The mechanism of action of synergists can be very different. They can deactivate those factors that promote oxidation, for example, deactivate traces of metals (Pb, Cu, Co, Mn, Fe, etc.) that act as oxidation catalysts. Active synergists are compounds that have hydroxy- and amino functions in the molecule. Citric and ascorbic acids have proven themselves as chelators. Phosphoric acid derivatives are also synergists.
The rate of fat oxidation decreases with decreasing oxygen content increases with increasing temperature, direct sunlight. In the body, lipid oxidation proceeds under the action of biological catalysts - lipoxygenases. Such enzymatic oxidation, which causes rancidity of oils, is characteristic of the lipid complex of stored oilseeds, grains, and products of their processing (flour, cereals). In all these objects, along with fats, there are enzymes of lipase and lipoxygenase. Each has its own purpose - lipase catalyzes the hydrolysis of triacylglycerols, and lipoxygenase catalyzes the formation of hydroperoxides of unsaturated fatty acids (mainly linoleic and linolenic). Free fatty acids are oxidized faster than their residues, which are part of the fat triglyceride molecule. Thus, enzymatic rancidity can be expressed by the following general scheme
And then, at the sites of lipoxygenase, the resulting unsaturated acid is oxidized to pore hydroxy compounds
The oxidation process can, as described above, proceed further. Forming hydroperoxy and secondary metabolites - aldehydes and ketones are the cause of deterioration in the quality of food raw materials and many lipid-containing products, the so-called rancidity of margarine, milk fat, flour, cereals. Therefore, lipid-containing products stored for a long time under the influence of air oxygen, moisture, light and the enzymes present in them gradually acquire an unpleasant taste and smell. Some of them are discolored. They accumulate harmful oxidation products. At the same time, not only their nutritional and biological properties are reduced, but they may turn out to be completely unsuitable for consumption.
Food spoilage of fat is accompanied by a change not only in triglycerides, but also in related substances. For example, the discoloration of vegetable oils during salting is associated with the oxidation of carotenoids. The dark color of oils obtained from moldy grains is due to the oxidation of mycotoxins accumulated in them. The very dark color of cottonseed oil is associated with the appearance of gossypol oxidation products. Deeper processes of fat spoilage are accompanied by the formation of both heavy polymerization products and light ones, for example, trimethylamine N (CH 3) 3 - it ensures that the products turn rancid with a herring smell. Fats and products containing them are not equally stable during storage, it depends on their fatty acid composition, the nature of the impurities present, the presence or absence of enzymes. All this determines the conditions of their packaging, storage, shelf life of finished products. The least stable during storage are margarine, butter and chicken fat.
Analysis of fat spoilage is carried out mainly organoleptically. At the first stage, an unpleasant taste appears, which is not characteristic of the oil or fat being evaluated (fat can act as an irritant - pinching in the throat, causing a burning sensation, scratching. A little later, an unpleasant odor appears (sometimes the smell of drying oil). In a qualitative assessment of spoilage of butter or margarine use the terms: "salting", "cheesy taste", "oiliness" and finally "rancidity".
Methods for the isolation and analysis of lipids in raw materials and food products
For the analysis of lipids, a wide variety of methods are used - classical and physico-chemical.
The study of lipids begins with the determination of their quantity (content) in foods. To do this, methods for determining the content of lipids directly in the object (NMR and IR spectroscopy) and methods for extracting lipids from food products or biological objects are used. When isolating lipids, it should be taken into account that they are capable not only of hydrophobic interactions, but also of the formation of hydrogen, electrostatic, and covalent bonds. Depending on the type of interaction, they are divided into free, bound or strongly bound. From this to what type lipids belong and methods for their extraction differ.
Free lipids extracted from a biological object with non-polar solvents (hexane, diethyl ether). In this case, the complexes formed by hydrophobic interactions in adipose tissue, albumin complexes with fatty acids are destroyed.
Related lipids are extracted by a solvent system in which a polar component is present, usually an alcohol (a mixture of chloroform and ethanol). This destroys the hydrogen and electrostatic forces. In this way, lipids are extracted from membranes and mitochondria.
Tightly bound lipids. They are in complexes formed by covalent bonds and are not extracted by solvents. First, the complex is destroyed by hydrolysis with weak acid or alkali solvents, and then the released lipids are extracted with an organic solvent.
All groups of lipids can be identified step by step.
In addition to extraction with organic solvents, extraction with liquefied gases (butine, nitrogen, ammonia, CO 2, freons, argon, etc.) is used. Since extraction takes place at lower temperatures, the risk of oxidation, decomposition and loss of valuable properties during evaporation is minimized. The most promising is the extraction of CO 2 (28 0 C, p=65-70 atm), the quantitative yield reaches 98%.
After isolation, the resulting lipid mixture is fractionated (separated into individual components) and analyzed. In general, the lipid analysis scheme is as follows:
triacylglycerides
diacylglycerides
monoacylglycerides
free fatty acids
sterols, vitamins, etc.
The most effective and widely used method of fractionation of complex mixtures of lipids is chromatography (adsorption). It is used for both analytical and preparative purposes. Thin layer chromatography is most effective. There are various methods of chromatographic separation (one-dimensional, two-dimensional, eluents of different polarity).
The main characteristics of lipids are:
Acid number(the definition has already been given) - an indicator that characterizes the amount of free fatty acids contained in fat. Given that the storage of food products containing fats and oils is always accompanied by the hydrolysis of the latter, one can judge their quality by the value of the acid number. In fat processing technology, acid number is used to calculate the amount of alkali required for alkaline refining of fats and oils.
Saponification number is equal to the number of mg of KOH required for saponification of glycerides and neutralization of released and free fatty acids in 1 g of fat or oil. By the number of saponification, one can judge the average molecular weight of the fatty acids included in the composition and determine the amount of alkali necessary for saponification of fat during soap making.
Iodine number- an indicator characterizing the unsaturation of fatty acids that make up fat. It is expressed as a percentage of iodine equivalent to halogen added to 100 g of fat. There are several methods for determining the iodine number. One of the most common is the bromometric method. In this case, a solution of bromine is used in anhydrous methyl alcohol saturated with NaBr, with which bromine forms a strong complex compound
Breaking off bromine reacts with unsaturated glycerides
Unreacted bromine is titrated iodmetrically.
and the released iodine is titrated with sodium thiosulfate.
And from here it is easy to calculate the iodine number of fat. The iodine number is widely used to determine the type of fat, its ability to "dry", the calculation of the hydrogen necessary for its hydrogenation.
Chemical synthesis of lipids
For research and practical purposes, lipids are usually isolated from natural sources. However, in some cases, chemical synthesis is necessary, for example, to finally prove the structure of new types of lipid substances isolated from plant, animal or mineral organisms, the development of membrane studies has put on the agenda the problems of preparative synthesis of many membrane lipids, in addition to the study of lipid functions, in the study of the mechanisms of their interaction with other components of living nature requires modified lipids, lipids containing a radiation label.
The complexity of the chemical structure of lipids and their great diversity require the use of a wide range of synthesis methods. But if you do not touch on the methods for obtaining saturated and unsaturated carboxylic acids, then they boil down to the following
1. Acylation hydroxyl groups of glycerol or amino groups of sphingosine. Fatty acids, their halides, and anhydrides are used as acylating agents.
2. Alkylation used in the synthesis of lipids with a simple ether bond. As reagents, alkyl halides or esters of p-toluenesulfonic acids are used.
3. Phosphating is an essential step in the synthesis of phospholipids. For this, chlorophosphates or silver salts of substituted phosphoric acids are obtained and they are involved in interaction with glycerol or sphingosine or their monohydroxy derivatives.
4. Glycosylation - it is used in the synthesis of glycolipids, a specific catalyst for glycosylation is mercury cyanide. Biocatalysts such as lipase can also be used.
The exchange reaction of functional groups in the presence of biocatalysts is also widely used.
Phospholipids of various types can also be obtained directly from phosphatidic acid by esterification with a suitable amino alcohol in the presence of a condensing agent.
All the described techniques are also suitable for the synthesis of sphingolipids.
Nutritional value of oils and fats
Vegetable fats and oils are a component of food, a source of energy and plastic material for a person, a supplier of a number of substances necessary for him (unsaturated fatty acids, phospholipids, fat-soluble vitamins). All these substances are indispensable nutritional factors that determine its biological value. The recommended fat content in the human diet is 30-33%. In the southern regions, it is somewhat less - 27-28%, and for the northern regions - more than 38-40%. On average, this is 90-102 g per day, directly in the form of fats 45-50 g. The constant rejection of fats or the use of only fats combined with the necessary components leads to serious disturbances in the physiological state of a person. The activity of the central nervous system is disrupted, immunity is reduced, life expectancy is reduced. Excess consumption of fat is undesirable. It leads to obesity and the occurrence of many cardiovascular diseases.
Visible fats (vegetable oils, animal fats, butter, margarine, etc.) and invisible fats (fat in meat and meat products, fish, milk, dairy products, cereals, bread and bakery products) are distinguished in the composition of food products. The largest amount of invisible fats is found in chocolate, sweets, cheese, sausages. It is important not only the amount of absorbed fat, but also its composition. Linoleic and linolenic acids are not synthesized in the human body; arachidonic acid is synthesized from linoleic acid. These three types of acids are essential. They are involved in the construction of cell membranes, prostaglandins, are involved in the regulation of metabolism, regulation of cell metabolism, blood pressure, platelet aggregation, and regulates many other processes. All these functions are performed only cis-isomers of unsaturated acids. In the absence of essential fatty acids, a variety of diseases develop. Of the essential acids, arachidonic acid has the highest activity, followed by linoleic acid, linolenic acid is 8-10 times less active than linoleic acid. Useful for the body are pentoenoic acids, which are contained in fish fat.
Among food products, vegetable oils are the richest in polyunsaturated acids, especially corn, sunflower, and soybean. The content of linoleic acid in them reaches 50-60%, in animal fats - only 0.6%. Arachidonic acid is found in food in small quantities. Most of all it is in eggs - 0.5%, and in vegetable fats there is practically none.
Currently, it is believed that the daily requirement for linoleic acid should be 6-10 g, the minimum is 2-6 g, and its total content in dietary fats should be at least 4% of the total calorie content. Thus, the composition of fatty acids intended for nutrition of a healthy body should be balanced: 10-20% - polyunsaturated, 50-60% monounsaturated and 30% saturated, some of which should be with an average chain length. This is ensured by using 1/3 of vegetable fats and 2/3 of animal fats in the diet.
Depending on age and those suffering from cardiovascular diseases, this ratio changes in favor of unsaturated ones: the ratio of polyunsaturated and unsaturated acids is ~ 2:1, and the ratio of linoleic and linolenic acids is ~ 10:1. It is believed that it is better to use fats of a balanced composition in one meal.
An important group of lipids in nutrition are phospholipids, which are involved in the construction of cell membranes and the transport of fat in the body, they contribute to better absorption of fats and prevent fatty liver. The total human need for phospholipids is 5 g per day. There are cholesterol restrictions. With an increase in its level in the blood, the risk of the occurrence and development of atherosclerosis increases. Daily intake of cholesterol should not exceed 0.5 g. The largest amount of cholesterol is found in eggs, butter and offal.
Carbohydrates
LECTURE #1
Carbohydrates are widely distributed in nature and play an important role in the life processes of various organisms. It should be noted that glucose is formed practically from nothing, being the first substances of a living cell along the biosynthetic pathway. If amino acids, and especially their polymeric derivatives, polypeptides and proteins, are more concentrated in living organisms, then carbohydrates in plants. They are widely distributed in nature and occur both in free and bound form. Carbohydrates account for ¾ of the entire biological world, cellulose is the structural unit of the plant world (80-90%), and the main dietary carbohydrate is starch. In the animal body, carbohydrates account for 2% of the mass.
Lipids are the most important source of energy in the body. The fact is obvious even at the nomenclature level: the Greek "lipos" is translated as fat. Accordingly, the category of lipids combines fat-like substances of biological origin. The functionality of the compounds is quite diverse, which is due to the heterogeneity of the composition of this category of bio-objects.
What are the functions of lipids
List the main functions of lipids in the body, which are the main ones. At the introductory stage, it is advisable to highlight the key roles of fat-like substances in the cells of the human body. The basic list is the five functions of lipids:
- reserve energy;
- structure-forming;
- transport;
- insulating;
- signal.
The secondary tasks that lipids perform in combination with other compounds include regulatory and enzymatic roles.
The energy reserve of the body
This is not only one of the important, but the priority role of fat-like compounds. In fact, part of the lipids is the source of energy for the entire cell mass. Indeed, fat for cells is an analogue of fuel in a car tank. The energy function of lipids is realized as follows. Fats and similar substances are oxidized in the mitochondria, breaking down to the level of water and carbon dioxide. The process is accompanied by the release of a significant amount of ATP - high-energy metabolites. Their reserve allows the cell to participate in energy-dependent reactions.
Structural blocks
At the same time, lipids perform a building function: with their help, the cell membrane is formed. The following groups of fat-like substances are involved in the process:
- cholesterol - lipophilic alcohol;
- glycolipids - compounds of lipids with carbohydrates;
- Phospholipids are esters of complex alcohols and higher carboxylic acids.
It should be noted that in the formed membrane, fats are not directly contained. The resulting wall between the cell and the external environment is two-layered. This is achieved due to biphilia. A similar characteristic of lipids indicates that one part of the molecule is hydrophobic, that is, insoluble in water, the second, on the contrary, is hydrophilic. As a result, the bilayer of the cell wall is formed due to the ordered arrangement of simple lipids. Molecules turn their hydrophobic regions towards each other, while hydrophilic tails are directed inside and outside the cell.
This determines the protective functions of membrane lipids. First, the membrane gives the cell its shape and even maintains it. Secondly, the double wall is a kind of passport control point that does not allow unwanted visitors to pass through.
Autonomous heating system
Of course, this name is rather conditional, but it is quite applicable if we consider what functions lipids perform. The compounds do not so much heat the body as they keep the heat inside. A similar role is assigned to fatty deposits that form around various organs and in the subcutaneous tissue. This class of lipids is characterized by high heat-insulating properties, which protects vital organs from hypothermia.
Have you booked a taxi?
The transport role of lipids is considered a secondary function. Indeed, the transfer of substances (mainly triglycerides and cholesterol) is carried out by separate structures. These are linked complexes of lipids and proteins called lipoproteins. As you know, fat-like substances are insoluble in water, respectively, in blood plasma. In contrast, the functions of proteins include hydrophilicity. As a result, the core of a lipoprotein is an accumulation of triglycerides and cholesterol esters, while the shell is a mixture of protein molecules and free cholesterol. In this form, lipids are delivered to the tissues or back to the liver for removal from the body.
Secondary Factors
The list of already listed 5 functions of lipids complements a number of equally important roles:
- enzymatic;
- signal;
- regulatory
Signal function
Some complex lipids, in particular their structure, allow the transmission of nerve impulses between cells. Glycolipids act as an intermediary in this process. No less important is the ability to recognize intracellular impulses, which is also realized by fat-like structures. This allows you to select from the blood the substances necessary for the cell.
Enzymatic function
Lipids, regardless of their location in the membrane or outside it, are not part of enzymes. However, their biosynthesis occurs with the presence of fat-like compounds. Additionally, lipids are involved in protecting the intestinal wall from pancreatic enzymes. The excess of the latter is neutralized by bile, where cholesterol and phospholipids are included in significant quantities.
