Fats
Lipids
Lipids are a large group of natural compounds, different in structure and function, but similar in physicochemical properties. Their characteristic feature is the high content of hydrophobic radicals and groups in the molecules, which makes them insoluble in water. However, lipids are highly soluble in various organic solvents: ether, acetone, gasoline, benzene, chloroform, etc.
Lipids are divided into 2 groups: fats and fat-like substances, or lipoids.
Vegetable fats are usually liquid and are called oils. Fats perform storage and energy functions and are found in small quantities in all plant cells. Typically, vegetative organs contain much less fat than fruits and seeds. Thus, in leaves, stems and roots, the amount of fat rarely exceeds 5% of the dry mass. At the same time, the fruits and seeds of some plants are high in fat and are used for the industrial production of vegetable oils.
Peas, beans 2
Corn 5
Soybean, flax, cotton 20-30
Sunflower, mustard 30-50
Peanuts, poppy seeds, olives 40-50
Sesame, castor beans 50-60
Coconut tree 65
Up to 90% of all plant species deposit oil in their seeds as the main reserve substance, which is used during their germination. The deposition of fats into the reserve for plants is energetically “beneficial”, since their breakdown releases almost 2 times more energy than the breakdown of carbohydrates or proteins, and also produces 2 times more water, which is especially important when seeds germinate under conditions insufficient water supply.
Vegetable oils find the widest application. They are used in food, in the food and perfume industries, in medicine, in technology as lubricating oils and in the manufacture of high-quality varnishes and paints.
Fats are a mixture of glycerol esters and high molecular weight fatty acids. They are called glycerides. Fats contain mainly triglycerides:
Vegetable oils obtained from seeds are not pure triglycerides, but always contain some amount of impurities. Triglycerides account for 95-98%, the rest are impurities: free fatty acids (1-2%), phospholipids (1-2%), steroids (0.3-0.5%), as well as fat-soluble carotenoids vitamins, terpenoids, phenolic compounds. The presence of impurities increases the nutritional value of vegetable oils. Many of them have a healing effect. The yellowish color of vegetable oils depends on the content of carotenoids in them. Hemp and bay oils, which contain some chlorophyll, have a greenish color.
The properties of fats are determined by the composition of fatty acids that form an ester bond with glycerol. Fatty acids, the residues of which are part of triglycerides, can be saturated, mono- and polyunsaturated, and contain cyclic and polar groups. They almost all have an even number of carbon atoms (C 6 -C 22) and an unbranched chain.
The most important saturated fatty acids in vegetable oils:
Name Formula Where found
Nylon C 6 H 12 O 2 Coconut oil (up to 1%)
Caprylic C 8 H 16 O 2 Coconut oil (7%)
Capric C 10 H 20 O 2 Palm oil
Lauric C 12 H 24 O 2 Laurel and palm oil
Myristic C 14 H 28 O 2 Tropical plant oil
Palmitic C 16 H 32 O 2 Widely distributed
Stearic C 18 H 36 O 2 Widely distributed
Arachidic C 20 H 40 O 2 Peanut oil, etc.
Behenic acid C 22 H 44 O 2 Peanut oil, rapeseed oil, etc.
The most important unsaturated fatty acids of vegetable oils:
Vegetable oils contain much more unsaturated fatty acids than saturated fatty acids, which determines their liquid consistency. Scientists have calculated that oleic and linoleic acids account for more than 60% of all fatty acids in vegetable oils.
Linoleic and linolenic acids cannot be synthesized by the animal body. They are essential fatty acids and must be supplied to the body daily with food.
The properties of fat are characterized by a number of physicochemical constants. We will look at three constants that are important in determining the quality of vegetable oils: melting point, acid value and iodine value.
Since vegetable oils are mostly liquid, the melting point is important for only a few solid oils. Solids at room temperature include cocoa butter, coconut oil, palm oil and bay oil. These oils contain many saturated fatty acids.
Cocoa butter is obtained from seeds that contain 45-55% fat. After its removal, cocoa powder remains, which is used to prepare the famous drink and in the confectionery industry. Cocoa butter has a yellowish color and a pleasant smell, its melting point is 30-34°C. Its triglycerides contain lauric, palmitic, stearic, arachidic and oleic acids. This oil is used in the confectionery and perfume industries.
Coconut oil is obtained from the pulp of coconuts - copra. Copra contains up to 60-65%. Its melting point is 23-28°C. At room temperature it is softer than butter and has a pleasant smell and taste. As part of triglycerides, it contains mainly lauric, myristic acids, as well as 2-3% caproic, caprylic and capric. Coconut oil is used in the food, perfume, soap industries, and in the manufacture of ointments. Soap made with coconut oil is the only one that foams in salty sea water.
The oil palm contains oil in its seeds and fruit. This oil is solid at room temperature. The oil from the fruit is inedible and is used as a lubricant and in the production of candles and soap. The seeds contain edible oil. It is used for food and for making ointments.
Bay oil, which is obtained from the seeds of the bay laurel, can only conditionally be called solid: it has a paste-like consistency. This oil has a greenish color due to the chlorophyll it contains and a peculiar odor that depends on the presence of the essential oil.
During long-term storage, fats and products containing them deteriorate - they become rancid, acquiring an unpleasant taste and smell. The cause of rancidity may be the action of oxygen in the air, microorganisms and enzymes (lipase and lipoxidase).
The most common is rancidity under the influence of oxygen in the air. In this case, oxygen oxidizes unsaturated fatty acids at the site of the double bond to form a peroxide or the carbon atom adjacent to the double bond to form a hydroperoxide.
Fat-like substances include:
Phospholipids
Sphingolipids
Glycolipids
Steroids
Cutin and suberin
Fat-soluble pigments
(chlorophylls, carotenoids, phycobilins).
Glycolipids - these are fat-like substances in the molecules of which glycerol is connected by an ester bond with two fatty acid residues and a glycosidic bond with some sugar. Glycolipids are the main lipids of chloroplast membranes. There are approximately 5 times more of them in photosynthetic membranes than phospholipids.
Steroids. The steroids are based on 4 fused carbocycles: 3 six-membered and 1 five-membered. In animal organisms, cholesterol and a number of hormones have a steroid nature. In plants, steroids are more diverse. More often they are represented by alcohols - sterols. About 1% of sterols are linked by ester bonds to fatty acids - palmitic, oleic, linoleic and linolenic.
Ergosterol is common in plants, as well as yeast, ergot horns, and mushrooms. Vitamin A is formed from it under the influence of ultraviolet light.
ergosterol-sitosterol
Sterols are part of plant cell membranes and are believed to be involved in the control of permeability. It was found that the bulk of plant cell sterols are contained in the membranes of the ER and mitochondria, and their esters are associated with the cell wall fraction.
Wax. Waxes are contained in the cuticle and form a thin layer on its surface. A waxy coating covers the leaves, stems and fruits, protecting them from drying out and being damaged by microorganisms.
Wax- These are fat-like substances that are solid at room temperature. The composition of waxes includes esters of fatty acids and monohydric high-molecular fatty alcohols. In addition, waxes contain free fatty acids and alcohols, as well as paraffin hydrocarbons.
The composition of waxes varies from plant to plant. For example, the wax of cabbage leaves consists mainly of C 29 -hydrocarbon and its derivatives containing the carbonyl group =C=O. Grape berry wax contains esters of palmitic acid, ceryl and myricyl alcohols.
Plant waxes are used in the manufacture of candles, lipsticks, soaps, patches, and shampoos. For example, a significant amount of wax is secreted on the surface of the leaves of the Palma ceprpega palm, which grows in South America - up to 5 mm. This wax is called carnauba wax. It is hard and brittle, yellowish-greenish in color, and is used to make candles.
A unique wax is found in the fruits and seeds of Simonzia Californian, or jojoba, native to the southwestern United States and northwestern Mexico. This wax is liquid. For a long time it was mistaken for oil. For a long time, the Indians have been eating it and using its medicinal properties (wound healing, etc.) - And only relatively recently did they find out that it does not contain triglycerides, but esters of high-molecular acids and monohydric alcohols. In addition, this wax is the only one so far that is a reserve nutrient and is used during seed germination.
Cutin and suberin - these are fat-like substances that cover or permeate the walls of the integumentary tissues (epidermis, cork), increasing their protective properties. Kutin covers the epidermis with a thin layer on top - cuticle, which protects underlying tissues from drying out and penetration of microorganisms. Cutin contains C16 and C18 fatty hydroxy acids - saturated and monounsaturated. Hydroxyl groups - from one to three - are located at the end, as well as in the middle, of the acid's carbon chain. These groups bond with carboxyl ester bonds, resulting in a complex three-dimensional cutin structure that is highly resistant to various influences.
Suberin- a polymer that impregnates the cell walls of the cork and primary root cortex after desquamation of root hairs. This makes the cell walls strong and impermeable to water and gases, which, in turn, increases the protective properties of the integumentary tissue. Suberin is similar to cutin, but there are some differences in the composition of the monomers. In addition to the hydroxy acids characteristic of cutin, suberin contains dicarboxylic fatty acids and dihydric alcohols. The bonds between monomers are the same - ester bonds, which are formed by the interaction of hydroxyl and carboxyl groups.
In food products of animal origin, the main representative of sterols is.
The amount of cholesterol in adults and children should not exceed 300 mg.
There is especially a lot of cholesterol in sour cream, butter, eggs, liver, kidneys, brains, tongue, fats (beef, lamb, pork), sturgeon caviar, fatty herring, saury, sardines (canned), halibut. These products should not be abused, since high cholesterol levels in the body are one of the main reasons for the development of atherosclerosis.
Participate in the regulation of cholesterol metabolism and promote its elimination. In food products of plant origin, lecithin is mainly found, which contains the vitamin-like substance choline, as well as cephalin.
Rich (2.5-3.5 g per 100 g of the edible part of the product): egg yolk, liver, caviar, rabbit meat, fatty herring, unrefined vegetable oils. In 100 g of beef, lamb, pork, chicken meat, and peas there is about 0.8 g of lecithin; in most fish, cheese, butter, oatmeal - 0.4-0.5 g, in full-fat cottage cheese and sour cream - 0.2 g.
The optimal content of phospholipids in the diet of an adult is 5-7 g/day.
They are of significant value to the body fat-like substances (lipoids). These include biologically active substances - phospholipids And sterols.
Phospholipids (phosphatides)– the main representatives are lecithin, cephalin and sphingomyelin. In the human body, they are part of cell membranes and are essential for their permeability, metabolism between cells and the intracellular space.
Phospholipids in food products differ in their chemical composition and biological effects. The latter largely depends on the nature of their constituents. amino alcohol.
Most widely represented in food products lecithin. Lecithin contains glycerin, unsaturated fatty acids, phosphorus and vitamin-like substance choline. Lecithin has lipotropic action - reduces the accumulation of fats in the liver, promoting their transport into the blood. It is part of the nervous and brain tissue and affects the activity of the nervous system. Lecithin is an important factor in regulating cholesterol metabolism, because prevents the accumulation of excess amounts of cholesterol in the body, promotes its breakdown and elimination. A sufficient amount of lecithin is of great importance in diets for atherosclerosis, liver diseases, cholelithiasis, in the diets of mental workers and the elderly, as well as in diets for therapeutic and therapeutic-and-prophylactic nutrition.
The daily need for lecithin is about 5 g. Eggs (3.4 g%), liver, caviar, rabbit meat, fatty herring, unrefined vegetable oils (2.5-3.5 g%) are rich in lecithin. Beef, lamb, pork, chicken meat, peas contain about 0.8 g% lecithin, most fish, cheese, butter, oatmeal - 0.4-0.5 g%, full-fat cottage cheese, sour cream - 0. 2 g%. A good low-fat source of lecithin is buttermilk.
Sterols are hydroaromatic alcohols of complex structure contained in vegetable oils (phytosterols) and animal fats (zoosterols).
The best known of the phytosterols is ß-sitosterol, most of it is found in vegetable oils. It normalizes cholesterol metabolism, forming insoluble complexes with cholesterol that prevent the absorption of cholesterol in the gastrointestinal tract, and thereby reduce its content in the blood.
Cholesterol refers to animal sterols. It is a normal structural component of all cells and tissues. Cholesterol is part of cell membranes and, together with phospholipids and proteins, ensures selective permeability of membranes and affects the activity of enzymes associated with them. Cholesterol is the source of the formation of bile acids, steroid hormones of the gonads and adrenal cortex (testosterone, cortisone, estradiol, etc.), vitamin D.
It should be highlighted relationship between dietary cholesterol and atherosclerosis, the causes of which are complex and diverse. It is known that cholesterol is part of complex plasma proteins lipoproteins. There are high-density lipoproteins (HDL), low-density lipoproteins (LDL) and very low-density lipoproteins (VLDL). TO atherogenic, those. promoting the formation of atherosclerosis include LDL and VLDL. They are capable of depositing on the vascular wall and forming atherosclerotic plaques, as a result of which the lumen of the blood vessels narrows, the blood supply to the tissues is disrupted, and the vascular wall becomes weak and fragile.
The bulk of cholesterol in the body is formed in the liver (about 70%) from fatty acids, mainly saturated. A person receives part of cholesterol (about 30%) from food.
The qualitative and quantitative composition of food significantly affects cholesterol metabolism. The more cholesterol comes from food, the less it is synthesized in the liver and vice versa. When saturated fatty acids and easily digestible carbohydrates predominate, cholesterol biosynthesis in the liver increases, and when PUFAs predominate, it decreases. Cholesterol metabolism is normalized by lecithin, methionine, vitamins C, B6, B12, etc., as well as microelements. In many products, these substances are well balanced with cholesterol: cottage cheese, eggs, sea fish, some seafood. Therefore, individual products and the entire diet must be assessed not only by cholesterol content, but also by a combination of many indicators. Currently, saturated fatty acids from animals and hydrogenated fats are considered more significant risk factors for the development of cardiovascular pathology than dietary cholesterol.
Cholesterol is widely present in all foods of animal origin (Table 3).
A typical daily diet should contain no more than 300 mg of cholesterol. When cooked, about 20% of cholesterol is destroyed.
Fats and fat-like substances (lipids) are derivatives of higher fatty acids, alcohols or aldehydes. They are divided into simple and complex. Simple lipids include lipids whose molecules contain only residues of fatty acids (or aldehydes) and alcohols. Among the simple lipids found in plants and animal tissues are fats and fatty oils, which are triacylglycerols (triglycerides) and waxes. The latter consist of esters of higher fatty acids and mono- or diatomic higher alcohols. Close to fats are trostaglandins, which are formed in the body from polyunsaturated fatty acids. By chemical nature, they are derivatives of prostanoic acid with a skeleton of 20 carbon atoms and containing a cyclopentane ring.
Complex lipids are divided into two large groups: phospholipids and glycolipids (i.e. compounds containing a phosphoric acid residue or a carbohydrate component in their structure).
Fatty oils of plants and fats of reserve tissues of animals, along with carbohydrates, represent a concentrated energy and construction reserve of the body. Up to 90% of plant species contain storage fats in their seeds. In addition to seeds, reserve fats can accumulate in other plant organs. Plants characterized by a high oil content in seeds and fruits in the tropics and subtropics are represented mainly by trees (palm trees, tung, castor beans, etc.). In areas with a temperate climate, these are mainly herbaceous plants (flax, sunflower, etc.), less often shrubs, and even less often trees. The accumulation of fats in plants can be quite significant; for example, in domestic sunflower varieties, the oil content sometimes reaches 60% of the kernel weight.
Spare fats also serve as protective substances that help the body endure unfavorable environmental conditions, in particular low temperatures. By accumulating in the endosperm or in the cotyledons of “overwintering” seeds, fats allow the embryo to be preserved in frost conditions. In trees in temperate climates, when entering a dormant state, the reserve starch of the wood turns into fat, which increases the frost resistance of the trunk. In animals, fats are final or temporary reserve substances. Finite reserves, such as milk fat, are not used by the body. Only temporary storage fats, typical of adipose tissue, are mobilizing products. It is these fats that simultaneously serve humans as products for food, medicinal and technical purposes.
Structure of fats
Fats consist almost exclusively of mixtures of fatty acid glycerides, which are esters of glycerol and high molecular weight fatty acids, most often triglycerides. Triglycerides have a general formula:
More than 200 different fatty acids are found in natural fats. The predominant ones are fatty acids with an even number of carbon atoms from C 8 to C 24. Fatty acids with a short chain of less than 8 carbon atoms (capronic, butyric, etc.) are not found in triglycerides, but they can be present in free form, affecting the smell and taste of fats. Most fats contain 4-7 main and several accompanying (constituting less than 5% of the total) fatty acids. Suffice it to say that up to 75% of global fat production is made up of triglycerides of three acids - palmitic, oleic and linoleic.
The fatty acids contained in triglycerides can be saturated or unsaturated. In table 1 shows the list and structure of fatty acids most often included in triglycerides. The fats of some plants contain specific fatty acids that are characteristic only of these plants. So, for example, castor bean oil contains hydroxy acid - ricinoleic acid, chaulmugro fatty oil is formed by glycerides of cyclic acids - hydrocarpic, chaulmugra, etc.
Triglycerides can be single-acid or mixed-acid (mixed). In mono-acid triglycerides, esterification of glycerol occurred with three molecules of the same fatty acid (for example, triolein, tristearin, etc.). However, fats consisting of monoacid triglycerides are relatively rare in nature (olive oil, castor oil). The formation of fats is dominated by the law of maximum heterogeneity: the vast majority of known fats are mixtures of different acid triglycerides (for example, stearin diolein, palmitino diolein, etc.). Currently, over 1,300 fats are known, differing in the composition of fatty acids in the multi-acid triglycerides they form.
Fat-like substances include:
Phospholipids
Sphingolipids
Glycolipids
Steroids
Cutin and suberin
Fat-soluble pigments
(chlorophylls, carotenoids, phycobilins).
Glycolipids - these are fat-like substances in the molecules of which glycerol is connected by an ester bond with two fatty acid residues and a glycosidic bond with some sugar. Glycolipids are the main lipids of chloroplast membranes. There are approximately 5 times more of them in photosynthetic membranes than phospholipids.
Steroids. The steroids are based on 4 fused carbocycles: 3 six-membered and 1 five-membered. In animal organisms, cholesterol and a number of hormones have a steroid nature. In plants, steroids are more diverse. More often they are represented by alcohols - sterols. About 1% of sterols are linked by ester bonds to fatty acids - palmitic, oleic, linoleic and linolenic.
Ergosterol is common in plants, as well as yeast, ergot horns, and mushrooms. Vitamin A is formed from it under the influence of ultraviolet light.
ergosterol 
-sitosterol
Sterols are part of plant cell membranes and are believed to be involved in the control of permeability. It was found that the bulk of plant cell sterols are contained in the membranes of the ER and mitochondria, and their esters are associated with the cell wall fraction.
Wax. Waxes are contained in the cuticle and form a thin layer on its surface. A waxy coating covers the leaves, stems and fruits, protecting them from drying out and being damaged by microorganisms.
Wax - These are fat-like substances that are solid at room temperature. The composition of waxes includes esters of fatty acids and monohydric high-molecular fatty alcohols. In addition, waxes contain free fatty acids and alcohols, as well as paraffin hydrocarbons.
The composition of waxes varies from plant to plant. For example, the wax of cabbage leaves consists mainly of C 29 -hydrocarbon and its derivatives containing the carbonyl group =C=O. Grape berry wax contains esters of palmitic acid, ceryl and myricyl alcohols.
Plant waxes are used in the manufacture of candles, lipsticks, soaps, patches, and shampoos. For example, a significant amount of wax is secreted on the surface of the leaves of the Palma ceprpega palm, which grows in South America - up to 5 mm. This wax is called carnauba wax. It is hard and brittle, yellowish-greenish in color, and is used to make candles.
A unique wax is found in the fruits and seeds of Simonzia Californian, or jojoba, native to the southwestern United States and northwestern Mexico. This wax is liquid. For a long time it was mistaken for oil. For a long time, the Indians have been eating it and using its medicinal properties (wound healing, etc.) - And only relatively recently did they find out that it does not contain triglycerides, but esters of high-molecular acids and monohydric alcohols. In addition, this wax is the only one so far that is a reserve nutrient and is used during seed germination.
Cutin and suberin - these are fat-like substances that cover or permeate the walls of the integumentary tissues (epidermis, cork), increasing their protective properties. Kutin covers the epidermis with a thin layer on top - cuticle, which protects underlying tissues from drying out and penetration of microorganisms. Cutin contains C16 and C18 fatty hydroxy acids - saturated and monounsaturated. Hydroxyl groups - from one to three - are located at the end, as well as in the middle, of the acid's carbon chain. These groups bond with carboxyl ester bonds, resulting in a complex three-dimensional cutin structure that is highly resistant to various influences.
Suberin - a polymer that impregnates the cell walls of the cork and primary root cortex after desquamation of root hairs. This makes the cell walls strong and impermeable to water and gases, which, in turn, increases the protective properties of the integumentary tissue. Suberin is similar to cutin, but there are some differences in the composition of the monomers. In addition to the hydroxy acids characteristic of cutin, suberin contains dicarboxylic fatty acids and dihydric alcohols. The bonds between monomers are the same - ester bonds, which are formed by the interaction of hydroxyl and carboxyl groups.
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