The structure and chemical composition of vegetables and fruits

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The structure and chemical composition of vegetables and fruitsThe bulk of the fruit consists of pulp (64.5-98.5% of the weight of the fruit). The cells that form the fruit pulp are covered with a thin membrane - cellulose, inside which there is protoplasm (in the form of separate threads), consisting of nitrogenous protein substances. The space between the protoplasm filaments is filled with cell sap, which is an aqueous solution of mineral and organic substances.

Insoluble substances contained in fruits are cellulose, hemicellulose (protopectin), insoluble nitrogenous substances, starch, insoluble minerals. The composition of soluble substances that form fruit juice include:

1) organic substances:

  • a) sugar (fructose, glucose, sucrose),
  • b) polyhydric alcohols (mannitol, sorbitol, inositol),
  • c) pentosans, pectin,
  • d) acids (malic, citric, tartaric, formic, benzoic, salicylic),
  • e) nitrogenous substances,
  • f) fat,
  • g) tannins (tannins),
  • h) dyes,
  • i) essential oils,
  • j) enzymes,
  • k) vitamins;

2) inorganic substances: salts of acids and bases.

The structure and chemical composition of vegetables and fruitsIn quantitative terms, the fruits are dominated by water (70-90%); insoluble substances are 2-8%, soluble - 7-16%.

Qualitatively, the composition of soluble and insoluble substances in vegetables and fruits is approximately the same, but the quantitative ratios of individual ingredients are different.

Water

Water is one of the main factors that determine the activity of the course of life processes in the body.

It is found in all cells, tissues and body fluids. In tissues, a significant part of the water is in bound form. All chemical and physicochemical reactions occur in the body in the aquatic environment. Water enters into many reactions; without it, the processes of hydrolysis, many reactions of oxidation, hydration, swelling of colloids, etc. cannot be carried out. Without water, the flow of plastic and energetic substances into tissues and the elimination of metabolic products from the body is unthinkable. The evaporation of water from the surface of the body is a powerful factor in the regulation of heat exchange in the body.

The structure and chemical composition of vegetables and fruitsThe great importance of water for the body is confirmed by the fact that its absence is tolerated by humans and animals much worse than hunger. Without water, an organism can exist for only a few days, while a person can endure a lack of food for more than a month.

Water is found in fruits and vegetables in a free and colloidal state.

Free water is contained in the cell juice of fruits and vegetables; sugar, acids, mineral salts and other substances are dissolved in it; it is easily removed when dried. Fruits and vegetables contain more free water than bound water. Water, which is in a strong bond with various substances (bound), cannot be separated from them without changing their structure, therefore it is absorbed more gradually, as it is released. In addition, mineral salts are dissolved in the water available in vegetables, including large amounts of potassium salts. As you know, potassium salts are rapidly excreted from the body in the urine; together with them liquid and table salt are removed. Therefore, the water received with vegetables and fruits does not stay in the tissues, but quickly leaves the body, thereby contributing to the removal of metabolic products from it, including nitrogenous toxins. The diuretic effect of vegetables and fruits, which contributes to the enhanced excretion of metabolic products, is widely used in medical nutrition, especially in case of cardiovascular failure, kidney disease.

The structure and chemical composition of vegetables and fruitsThere is especially a lot of water in cabbage (white cabbage, cauliflower, red cabbage), onions, lettuce, spinach, sorrel, eggplant, zucchini, cucumbers, tomatoes, watermelon, oranges, tangerines, melon and etc.

Nitrogenous substances

The protein content of plants, in particular vegetables and fruits, is variable. The culture, plant variety, soil and climatic conditions have a great influence on the accumulation and amino acid composition of proteins. Fertilization, especially nitrogen fertilization, is of great importance. The nutritional value of proteins is determined by their digestibility and amino acid composition. The proteins contained in plant products are enclosed in fiber and are difficult to access by digestive enzymes, as a result of which the absorption of these proteins in the intestine is less complete than the absorption of animal protein. Vegetable proteins, freed from fiber, are absorbed as well as animals.

The vast majority of vegetables, all fruits and berries contain little nitrogenous substances - from 0.4 to 1.5%. Only dry legumes are rich in protein: peas contain 19.8% protein, soybeans - 28.7%, beans - 19.6%, lentils - 20.4%. Young leguminous vegetables are low in protein, such as green legumes 6%, green peas 5%.

Of the proteins found in vegetables and fruits, only pea, soy and lentil proteins contain all the essential amino acids and are complete. The proteins of other vegetables and fruits lack certain essential amino acids, so most plant proteins are less valuable than animal proteins.

The structure and chemical composition of vegetables and fruitsGiven the low protein content in vegetables and fruits, the lack of a number of essential amino acids, more difficult digestibility of vegetable proteins, it can be said that vegetables and fruits, with the exception of legumes, do not represent significant value as a source of protein in the diet of a healthy person. In medical nutrition, in some cases, a small amount of protein in vegetables and fruits is useful. Thanks to this, vegetables and fruits are widely used in diets for kidney diseases and in all cases when it is necessary to limit the intake of protein for a while.

Essential oils

Essential oils are found in fruits and leaves, causing their smell and aroma. They are called oils not because they have a relationship with fatty oils by their chemical nature, but because of the external similarity of their physical properties. They are poorly soluble in water, float on its surface in the form of oil eyes, when shaken give an unstable emulsion of a milky appearance, leave an oil stain on paper, easily dissolve in alcohol, ether, chloroform.

Essential oils are found in large quantities in citrus fruits and in some vegetables - onions, parsley, radishes, radishes, dill, celery, and garlic. They have disinfectant and antiseptic properties; on the skin and mucous membranes have a local irritant effect, causing burning, redness and inflammation. In addition, essential oils increase the secretion of digestive juices. They are excreted by the kidneys in the form of a compound with glucuronic and sulfuric acids. In small doses, they cause increased urine separation, in large doses, they have an irritating effect and can even cause severe nephritis. Excreted in part by the lungs, these substances increase the secretion of mucus and thereby promote expectoration, acting at the same time as an antiseptic. Essential oils affect the nervous system at first stimulating, and subsequently depressing.

In connection with the above properties of essential oils, the use of vegetables and fruits rich in them in small quantities is very advisable. Vegetables rich in essential oils are used as snacks and condiments to various dishes.

In medical nutrition, the appointment or prohibition of vegetables and fruits - ethers - is determined by the nature of the pathological process. For example, with gastric ulcer and duodenal ulcer, with enteritis, colitis, acute nephritis, hepatitis and cholecystitis, vegetables and fruits rich in essential oils are excluded from the patient's diet.With neuroses, accompanied by exhaustion and a simultaneous loss of appetite, the introduction of ether carriers is advisable.

Organic acids

The structure and chemical composition of vegetables and fruitsMany fruits and vegetables contain significant amounts of organic acids. Most often, fruits and vegetables contain malic and citric acids. Some fruits and berries contain small amounts of succinic, oxalic, salicylic, benzoic, formic acids.

Malic acid is found in almost all fruits. There is a lot of it in the rowan, barberry, dogwood, but not in citrus fruits and cranberries. Malic acid predominates in apples, citric acid in lemons (6-8%). There is a lot of citric acid in citrus fruits, in berries (in particular, in cranberries). Tartaric acid is found in significant quantities only in grapes. Small amounts of it are found in red currants, gooseberries, lingonberries, sweet cherries, strawberries, quince, apricots, plums.

Oxalic acid is found in small amounts in many fruits and vegetables and in significant amounts in spinach, sorrel, rhubarb, figs... In the intestine, it combines with dietary calcium and forms insoluble salt with it, which prevents its absorption. Many fruits and berries contribute to the excretion of oxalic acid from the body. These include apples, pears, quince, dogwood, leaves black currant, grape leaves (in the form of infusion). This is the basis for their use in oxaluria.

Succinic acid is found in unripe cherries, currants, cherries, apples, unripe gooseberries and grapes. Benzoic acid is found in lingonberries and cranberries; it has antiseptic properties. Salicylic acid is found mainly in strawberries, raspberries and cherries. Raspberry contains formic acid.

The amount of organic acids determines the overall acidity of the fruit or its juice. The taste of the fruit depends not only on the content of organic acids, but also on the type of sugars present in them (glucose, fructose or sucrose), on the presence of tannins (tannins), as well as on their various combinations.

The structure and chemical composition of vegetables and fruitsOrganic acids are among the strong causative agents of pancreatic secretion (NI Leporakii) and stimulate intestinal peristalsis (LB Berlin).

Thus, the inclusion of vegetables and fruits rich in organic acids in the diet contributes to the normal course of digestion.

Tannins (tannins)

Tannins are widespread in fruits. They are of great gustatory value: the astringent, tart taste of some fruits (blueberries, dogwood, quince, pears, etc.) depends on them. These substances cause the surface of a fresh cut of some fruits to darken in air, which is associated with the action of an enzyme from the group of oxidases. The amount of tannins in fruits decreases when frozen, so many fruits (mountain ash, dogwood) become less tart and less astringent after freezing.

Tannins have the ability to precipitate protoplasmic proteins of tissue cells and intercellular substance. Therefore, tannins have a local astringent or irritating effect on the mucous membranes, depending on their concentration in the solution. The precipitated protein layer protects the mucous membrane from various irritations to some extent. As a result, peristaltic bowel movements, especially if they were abnormally increased, slow down; food masses remain in its cavity longer than usual and absorption occurs in large sizes, despite the fact that tannins themselves impede absorption by the mucous membrane. As a result, the intestinal contents become harder and drier.

The anti-inflammatory effect of tannins on the intestinal mucosa leads to a decrease in its secretory function and is to some extent accompanied by an antiseptic effect.

Of the tannins, tannin is the best studied. It has anti-inflammatory, disinfectant and partially vasoconstrictor effect, has a beneficial effect on the intestines when diarrhea... The effect of tannin on the mucous membrane of the digestive tract after eating is very small, since the protein substances of the food bind it before it reaches the walls of the stomach and intestines.

Some of the tannin-rich fruits such as blueberry and bird cherry are used in medical nutrition for diseases of the gastrointestinal tract as an astringent and anti-inflammatory agent.

Carbohydrates

Vegetables, fruits and berries contain the following carbohydrates: monosaccharides - a-glucose and a-fructose; disaccharides - sucrose (beet sugar) and maltose (malt sugar); polysaccharides - starch, cellulose, hemicellulose, pectin substances, pentosans. Mono- and disaccharides, being water-soluble carbohydrates, determine the sweet taste of the fruit. They are rich in figs, grapes, apples, cherries, dates, persimmon, bananas.

Glucose and fructose are found in all fruits. Sucrose in some fruits such as grapes, red currants, cloudberries, dogwood, persimmon, missing. Pome fruit is dominated by fructose. In stone fruits (apricots, peaches, plum) glucose is slightly higher than fructose; they are richer in sucrose than pome fruits. Berries have the lowest sucrose content. The amount of fructose and glucose in them is approximately the same. When grapes ripen, the fructose content increases. Of tropical fruits, the largest amount of sugars is found in bananas; sucrose prevails in pineapples (8.6%). Citrus fruits contain a lot of sucrose, with the exception of lemons, where it contains up to 0.7-0.8% (with the simultaneous presence of a large amount of citric acid - 6-8%).

The structure and chemical composition of vegetables and fruitsThe sugar content varies greatly not only in fruits of different species and varieties, but also in fruits of the same variety grown under different climatic and soil conditions.

Sugars are mildly laxative.

The most important plant carbohydrate belonging to the group of polysaccharides is starch. It consists of amylose (80-85%) and amylopectin (15-20%). Starch is found mainly in green unripe fruits, as the fruit ripens, the amount of starch in it decreases.

Vegetables rich in starch include potatoes (average 16% starch) and green peas (average 6%). Bananas contain a lot of starch. There is very little starch in berries.

The starch of plant products is well digested in the gastrointestinal tract. Starchy vegetables and fruits are good sources of carbohydrates.

The backbone of plant food products is made up of cell membranes and middle plates located between them, firmly gluing individual cells. DI Lobanov calls these structural elements "cell walls". The median plates are composed of pectin substances. The main substance in cell walls, as mentioned above, is fiber (cellulose). It does not dissolve in water and is not destroyed by weak acids and alkalis. In terms of its chemical composition, it is a polysaccharide having the same chemical formula as starch, but a different arrangement of glucose particles. Individual vegetables and fruits differ in the content of "cell walls": in table varieties of carrots, cell walls are one and a half times more than in beets (on dry matter). In different varieties of the same vegetables, the "cell walls" are fairly constant.

Zucchini contains the least amount of fiber and cell membranes, onion and tomatothere are relatively few of them in lettuce, pumpkin, spinach, cabbage and potatoes. A lot of fiber and cell membranes in carrots, beets and most of all in green peas, beans and dry fruits.

Fiber is not digested at all by the digestive juices of the human gastrointestinal tract. The cell membranes are partially cleaved in the lower part of the small intestine and in the large intestine, mainly in the cecum, under the influence of the cellulase enzyme produced by bacteria; the result is glucose.However, in the large intestine, glucose is absorbed in negligible amounts that have no practical value (LB Berlin). The role of fiber and cell membranes in digestion is that they irritate the mechanoreceptors embedded in the walls of the gastrointestinal tract, thereby affecting the motor and secretory activity of the digestive organs.

The structure and chemical composition of vegetables and fruitsThe degree of mechanical irritation is determined by both the number and the state of the cell membranes: its intensity decreases with grinding and cooking food /

SI Chechulin on dogs, and later I.T.Kurtsip in observations of people showed that mechanical irritation of the stomach causes the secretion of gastric juice. I. T. Kurtsin found that bile formation and contractions of the gall bladder also intensify.

Mechanical irritation has a particularly great effect on the motor and secretory functions of the small and large intestines, strengthening them.

Eating foods rich in cell membranes increases the excretion of cholesterol from the body. When rabbits were fed milk and eggs, pronounced atherosclerotic changes in the aorta were noted; when given the same amount of pure cholesterol on a plant-based diet, these changes did not occur.

B.I.Barskiy established that the load of plant food against the background of a mixed diet leads to the mobilization and elimination of significantly larger amounts of sterols with feces than when feeding without such a load. As a load, the author added to the daily diet 200 g of carrots, 250 g of white cabbage, 100 g of beets and 700 g of apples. Based on this, he suggests that fiber adsorbs sterols and prevents their reabsorption.

Thus, fiber is essential for the normal course of digestion. Fiber-rich vegetables and fruits should definitely be included in the diet of a healthy person, although they do not significantly affect the calorie content of food. The effect of fiber on the digestive organs is taken into account when constructing therapeutic food regimes: in some cases, they try to introduce as large amounts of fiber as possible (for example, with constipation), in others, foods rich in fiber are limited or excluded from the diet (with gastric ulcer and duodenal ulcer in stages of exacerbation, with enteritis and colitis).

Pectin substances are complex colloidal polysaccharides called gluopolysaccharides. Their chemical nature and structure are not entirely clear. It is known that their molecule includes two components: some polysaccharide and pectic acid. The name of these substances comes from the word pectys - jelly - due to the ability of calcium salts of pectinic acid to form characteristic jellies.

Pectin substances form an intercellular layer (middle plate) in plant tissues, being a cementing material between individual cells. In plants, they are found in the form of protopectin and pectin. Immature fruits contain protopectin, which is insoluble in water and as an intercellular substance, which determines their density. When fruits ripen, protopectin transforms into soluble pectin, in connection with which the intercellular substance softens and the fruits acquire the softness characteristic of mature fruits. Protopectin can be converted to pectin by the action of the enzyme protopectinase or by prolonged boiling. This produces methyl alcohol and pectic acid. Methyl alcohol is formed similarly in unripe and spoiled fruits and berries.

The structure and chemical composition of vegetables and fruitsCurrently, there is evidence that pectin passes unchanged through the digestive tract up to the large intestine, where it is exposed to the microflora [Kertezh (Z. J. Keg-tesz)]. The completeness of the breakdown of pectin substances in the body is influenced by factors such as the rate of passage of food residues through the large intestine, the pH value of the intestinal contents, which varies within a fairly wide range, and the composition microflora, which can change dramatically depending on the nature of the previous diet or in connection with diseases such as dysentery. Pectin and its hydrolysis products help detoxify certain substances that enter the body, which has been shown for lead and menthol.

Works by a number of authors [Block, Tarnowski, Green; Myers, Rouse (L. N. Block, A. Tarnowski, V. N. Green; R. V. Myers, A. N. Rouse)] established a positive effect of pectin preparations, in particular nickel pectinate, in gastrointestinal diseases. It is explained mainly by the adsorbing properties of pectins, due to which bacteria and toxins are removed from the intestine (L.A. Pevnitsky, V.E. Kremer, N.F. Zaitseva, V.L. Ushakova, V.M. Golubeva) and water binds ... The presence of pectin in food can lead to some change in the intestinal microflora (according to N. V. Kuibysheva). According to Werch et al. (S. C. Werch and oth.), This action of pectin substances, if any, is caused rather by the acidic nature of the pectin compounds than by any specific properties.

Pectin substances are also attributed to bactericidal properties. Steinhaus, Georgi (I. E. Stein-haus, SE Georgi) are of the opinion that not the pectin itself, but the products of its decomposition in combination with other compounds have bactericidal properties.

The observations of Tompkins, Crook, Haynes, Winters (C. A. Tompkins, G. W. Crook, E. Haynes, M. Winters) found that pectin promotes epithelialization of tissues in the treatment of burns and infected wounds, thereby accelerating healing. The introduction of pectin into the gastrointestinal tract of animals protected the mucous membranes from damage caused by the action of menthol and atophan [Menville, Bradway, Mac Minis; Winters, Peters, Crook (J. A. Manville, E. M. Bradway, A. S. McMinis; M. Winters, G. A. Peters, G. W. Crook)].

Plant diets (apple, carrot, banana) used by many authors in the treatment of gastrointestinal diseases are rich in pectin substances. Most authors attribute a therapeutic effect to this circumstance.

So, the vast majority of fresh fruits and vegetables contain a relatively low amount of carbohydrates (no more than 10%). Fresh vegetables are only potatoes, and from fruits, some grape varieties contain quite a lot of carbohydrates, but much less than cereals and cereals. Dried fruits contain almost the same amount of carbohydrates as cereals and cereals. A significant part of carbohydrates in vegetables and fruits is contained in an easily digestible form (in the form of sugars), while in cereals and cereals carbohydrates are in the form of starch. Of the fruits, grapes are of great value, since carbohydrates are in it in significant quantities and in an easily digestible form.

The structure and chemical composition of vegetables and fruitsVegetables and fruits usually cover a small portion of the daily carbohydrate requirement, but they are nevertheless essential for the body. This is explained by the following:

  1. In fruits, carbohydrates are found mainly in the form of sugars and therefore are easily absorbed.
  2. A variety of dishes with added sugar are prepared from fruits (jelly, compotes, mousses, jellies, preserves, jams, etc.), therefore, with fruit dishes it is easy to introduce large amounts of water-soluble carbohydrates into the body, which is especially important to take into account in medical nutrition.
  3. Vegetables and fruits contain carbohydrates that, while not providing nutritional value, are nevertheless needed for the normal course of a number of physiological processes in the body (fiber, pectin).

Summarizing all of the above, we can say that vegetables and fruits, along with cereals, cereals and sugar, are a source of carbohydrates in the diet.

E. A. Beyul


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