Vegetables play an extremely important role in human nutrition. The nutritional value of vegetable crops is determined by their high content of carbohydrates, organic acids, vitamins, active elements, aromatic and mineral substances in a form accessible for absorption by the body. The variety and different combination of all the listed components in the composition of vegetable plants determines their taste, color, smell and nutritional value. The main indicator of the quality of vegetables is their biochemical composition. Vegetable plants contain up to 97% moisture in their composition, but even that small amount of dry matter found in vegetables contains many biologically important compounds that are vital for the normal functioning of the human body. The main part of the dry matter in vegetables is carbohydrates, the most important of which are starch and sugar.
The starch content in legumes is especially high, potatoes, root vegetables, carrots, peas, onions are rich in sugars. Sugars are present in vegetables various forms; Thus, table beets contain predominantly sucrose, while glucose predominates in cabbage, cucumbers and pumpkin crops.
The dry matter of vegetables also includes fiber, which has a positive effect on the body’s restoration of strength, and pectin substances, mainly proteins and glucose. Of particular value are natural organic acids, contained in different quantities in vegetable plants: lemon, apple, wine, oxalic and some others. It is organic acids that have a beneficial effect on the taste of vegetables and contribute to their better absorption by the human body. Many vegetable plants, such as onions, garlic, and aromatic crops, contain essential oils, possessing phytoncidal properties. The phytoncidal effect of onions and garlic has been used since ancient times in folk medicine for the purpose of prevention and treatment
inflammatory and infectious diseases.
Vegetables are also an important source of mineral elements involved in essential metabolic processes in the human body. Parsley leaves, green peas, onions, cabbage, and parsnips are exceptionally rich in phosphorus; leafy vegetables and root vegetables - potassium; lettuce, spinach, beets, cucumbers and tomatoes - iron; cauliflower, types of salads, spinach, greens - calcium.
The most valuable components of vegetables are the various vitamins they contain in large quantities, which are vital for human life. A lack of any vitamin in the human body can lead to serious disorders. various systems and cause serious illness. Vitamins are organic compounds necessary to maintain normal metabolism. They cannot be synthesized by the human body in the required quantities and must be supplied with food.
Vegetables are one of the main sources of replenishing vitamins in the body.
A person’s daily requirement for vitamins must be met to maintain their optimal balanced level in the body and the functioning of all systems. For example, daily dose, which satisfies the body's need for vitamin C, is contained in 300 g of ripe tomatoes, 250-300 g of fresh radishes, 250 g of fresh white cabbage, 80 g of dill, 70 g of parsley, 50 g of sweet pepper.
Fruits and vegetables contain vitamins, mineral salts, carbohydrates, proteins, and vegetable fats necessary for human life. Each type of fruit and vegetable has certain biological active substances: some of them improve the metabolic process, neutralize acids formed during the digestion of meat, dairy and flour foods, normalize blood pressure, others strengthen the walls of blood vessels, give them elasticity, and reduce cholesterol in the blood and fluids in the body.
Fruits and vegetables consumed fresh contain the most vitamins.
Provitamin A (carotene) is a growth vitamin. There is a lot of it in carrots, spinach, tomatoes, onion leaves, parsley, in the fruits of sea buckthorn, plums, and rose hips. In the human body, carotene is converted into vitamin A. With its deficiency, eye disease (night blindness) develops and the body's resistance to other diseases decreases.
B vitamins (Bi, Br, Bb, PP, etc.) promote metabolism in the body, slowing down the development of sclerotic phenomena in blood vessels. With a lack of vitamin Bi, a disease known as “beriberi” develops, which is characterized by a severe disorder of nervous and cardiac activity. Vitamin Br is part of a number of enzymes involved in carbohydrate and protein metabolism. With its deficiency, growth retardation or weight loss, weakness, weakened vision and the formation of cataracts, skin and nervous disorders. Vitamin PP takes an active part in metabolism. If it is deficient, the functions of the gastrointestinal tract are impaired. intestinal tract, central nervous system. Sources of vitamins Bi, Br and PP are apples, pears, carrots, tomatoes, cabbage, spinach, onions, and potatoes.
Vitamin C (ascorbic acid) protects against scurvy, nervous system disorders and general loss of strength. The main sources of this vitamin are rose hips, sea buckthorn, black currants, strawberries, apples, peppers, kohlrabi, white cabbage (fresh and pickled), horseradish, spinach, lettuce, onion leaves, dill and parsley, potatoes. Vitamin U contained in cabbage juice has been discovered. It helps treat stomach and duodenal ulcers.
Some vegetables contain aromatic substances that increase appetite and promote the absorption of food (dill, tarragon, cumin, basil, marjoram, savory, parsley, celery, onion, garlic, etc.); phytoncides that have a detrimental effect on pathogens (onions, garlic, peppers, radishes, horseradish).
Rational human nutrition consists of animal food and plant origin. Physiological norm consumption, the favorable temperature for growth, development and fruiting of heat-loving vegetable crops is 20-30 °C.
Less demanding of heat are cabbage of all types, carrots, beets, turnips, rutabaga, radishes, radishes, parsley, celery, onions, garlic, lettuce, spinach, dill, peas, and beans. Their seeds germinate at temperatures below 10 °C. These crops grow well, develop and form a productive part at 17-20 °C.
Winter-hardy vegetable plants include sorrel, rhubarb, horseradish, and perennial onions. In plants of this group, growth begins at 1-2 °C. Vegetating plants can tolerate frosts down to -10 °C. Being at rest, they overwinter painlessly in the open ground.
During the period of growth and development, the requirements for temperature conditions in vegetable plants change. During swelling and germination of seeds, more heat, and when seedlings appear, it is lower. Therefore, in protected ground with elevated temperature and lack of light, stretching of plants is often observed. During the flowering and fruiting period, the temperature should be elevated.
When storing vegetables and fruits it is necessary low temperature- about 0 ° C to slow down the processes of respiration and breakdown of nutrients.
Light. IN natural conditions sunlight- the only source of energy that provides the process of photosynthesis. In the light, synthesis occurs in the leaves of vegetative plants. organic matter from carbon dioxide in the air, water and minerals coming from the soil. The need for lighting is determined by the species and varietal characteristics of plants, the growing season, as well as the regime of other meteorological, soil and agrotechnical factors.
Garden plants react differently to light: some need intense lighting and, with a lack of light, grow poorly and sharply reduce yield (cherry), others are shade-tolerant (actinidia). The highest light intensity required reproductive organs(inflorescences, flowers, fruits). In the absence of light they do not develop. Deviation from the optimum illumination leads to leaf shredding. With insufficient lighting, many physiological processes are disrupted (accumulation and metabolism, differentiation of tissues and cells, pollination and fertilization, formation of fruits and seeds, etc.). For normal growth and high productivity of plants, it is necessary that all vegetative and reproductive organs that make up the crown are provided with an optimal amount of light. Poor lighting inside the crown reduces the longevity of the fruiting organs, their productivity, and the quality of the fruit. Assimilation, that is, the assimilation by the plant of what enters it from external environment substances is directly dependent on the intensity of illumination. As the latter improves, it increases. In gardening practice, pruning is used to lighten the crowns of trees and shrubs; if the planting is too dense, the plants are thinned out.
Vegetable crops are divided into short-day plants (tomatoes, eggplants, peppers, beans, zucchini, squash, pumpkin, cucumber varieties intended for cultivation in open ground) and long-day plants (root vegetables, cabbage, onions, garlic, green crops, some greenhouse varieties cucumbers). First for more rapid growth and development requires a day length of less than 12 hours, but in good light, the second requires more than 12 hours, and they tolerate partial shading.
By artificially shortening or lengthening daylight hours, you can get higher yields of some vegetable crops and products best quality. For example, by creating a short daylight hours for radishes, lettuce, dill and spinach, you can delay their development, that is, the transition to bolting and flowering, and get a higher yield of the productive part (root crops, leaves), and of increased quality. Under natural conditions, this is achieved by early spring and late autumn sowing dates, when daylight hours are shorter. IN winter months, with a short daylight hours and low illumination in greenhouses, from the moment of emergence of seedlings until the seedlings are planted in a permanent place, artificial supplementary lighting with electric lamps is used.
Excessive thickening of crops and plantings should not be allowed, both in protected and open ground, since in this case the plants shade each other, stretch out, weaken and subsequently reduce productivity. It is necessary to maintain the optimal density of sowing and planting, thin out the plantings if they are thickened, and destroy weeds.
Water makes up 75-85% of the wet weight of plants. It is spent on the formation of roots, shoots, leaves, fruits and other plant organs. great amount water. So, to create 1 kg of dry matter, plants consume 300-800 kg of water. Most of it is spent on transpiration, which promotes the movement of water through the vessels of the stem from the roots to the leaves.
The main source of water for the plant is soil moisture. Garden, vegetable and ornamental plants grow and produce best when soil moisture is 65-80% of full moisture capacity. With higher humidity, the oxygen necessary for the normal functioning of roots is displaced from the soil; with lower humidity, the plants lack moisture and their growth is inhibited.
In the Non-Chernozem Zone, with an annual precipitation of 550-700 mm, natural moisture is considered sufficient. However, every year certain months, and sometimes the entire growing season, are dry, as a result of which the normal growth and productivity of fruit, vegetable and ornamental plants is impossible without artificial irrigation. This is especially true for moisture-loving plants grown on light sandy and sandy loam soils, where constant watering is required.
If there is a lack of water for irrigation during the dry period, it is recommended to loosen the soil more often between the rows. Loosening prevents the formation of a soil crust, destroys the capillaries through which water flows from the lower layers of the soil to the upper ones, which significantly reduces its evaporation from the soil.
It is not recommended to water plants during the daytime in sunny weather, as most of the poured water will quickly evaporate. Watering is best done in the evening - 2-3 hours before sunset or early in the morning. In cloudy weather, watering during the daytime is also acceptable.
Fruit and berry plants more water required during the period intensive growth roots and shoots and during the formation of fruits (May - July), less - during the period of attenuation of growth and ripening of fruits (August - September). In dry weather, in the first period it is necessary to carry out abundant watering, in the future it can be limited, since a decrease in humidity at this time contributes to the ripening of shoots, preparing them for winter, ripening of fruits, improving their taste and color. Excessive amounts of moisture in the soil are also harmful: root growth is inhibited, shoot growth is delayed, fruits and berries crack. Trees and shrubs grow best when the groundwater level is at least 1-1.5 m from the soil surface. According to the degree of resistance to excess water in the root layer of the soil, fruit and berry plants are arranged in the following descending order: currants, gooseberries, apple trees, pears, plums, cherries, raspberries, strawberries.
Vegetable plants are demanding of moisture. IN different periods This exactingness varies depending on their growth and development. Cabbage, cucumbers, turnips, radishes, radishes, lettuce, and spinach are especially moisture-loving. A lot of moisture is required for seed germination (from 50 to 150% of their mass). Plants also need a lot of moisture at seedling age. Plants in adulthood and especially during the formation of productive organs need less frequent, but more abundant watering, capable of moistening the soil to the entire depth of the bulk of the roots (up to 20-30 cm). Plants must be watered regularly so that the moisture content of the root layer of soil is 70-80% of the total moisture capacity. A sharp transition from an arid state to excessive soil moisture leads to cracking of fruits, heads of cabbage and root crops, causing their consumer qualities to sharply decrease.
All thermophilic vegetable crops(especially cucumbers and tomatoes) should be watered with warm water (20-25°C). Watering cold water(6-10°C) leads to plant disease.
In greenhouses and greenhouses, water for irrigation is heated artificially. In open ground conditions, water is heated in the sun, for which it is poured in advance into barrels, bathtubs, tanks, and into small pools specially built on the plots.
Maintaining a certain air humidity is also important for vegetable plants. For example, the relative air humidity when growing cucumbers should be at least 85-90%, for tomatoes no more than 60-65%. Such a sharp difference in air humidity requirements does not allow growing cucumbers and tomatoes in the same greenhouse or greenhouse.
Atmospheric air consists mainly of oxygen (21%), carbon dioxide (0.03%) and nitrogen (78%). Air is the main source of carbon dioxide for photosynthesis occurring in plants, as well as oxygen necessary for their respiration (especially for the root system). Thus, adult plants per 1 hectare daily absorb more than 500 kg of carbon dioxide, which, if its content in 1 m3 of air is 0.03%, corresponds to more than 1 million m3. To ensure the normal functioning of plants, it is necessary to constantly replenish the air in the area where they are located with carbon dioxide. An artificial increase in the carbon dioxide content in the air to 0.3-0.6% (10-20 times more than natural) helps to increase plant productivity. The introduction of manure and other organic fertilizers into the soil helps enrich the ground layer of air with carbon dioxide. In greenhouses, this is achieved by fermenting cow or bird droppings in barrels, using liquefied gas cylinders, special burners, and “dry ice” (solid carbon dioxide).
The oxygen content in the soil air is somewhat less, and the carbon dioxide content is many times higher than in the atmosphere. Soil aeration has a great influence on the supply of oxygen to plant roots. To improve it, you need to frequently loosen the soil and keep it free of weeds.
Nutrition. To build their organs and produce crops, plants use minerals from the air (carbon dioxide) and soil (macro- and microelements dissolved in water). Different nutrients play different roles in plant life. Thus, carbon, oxygen, nitrogen, phosphorus, sulfur and magnesium are used to build organs and tissues. Iron, copper, zinc, manganese, cobalt are part of biocatalysts that promote the absorption of minerals by plants. Nitrogen, potassium, phosphorus, calcium, magnesium, sulfur are required by the plant in large quantities and are called macroelements, other elements are needed in small quantities and are called microelements. Of the macroelements, plants use nitrogen, phosphorus and potassium the most. Each of these elements is part of organic substances and plays a specific role in physiological processes.
Nitrogen is part of proteins and other organic substances. The largest amount of it goes to the formation of leaves, shoots, vegetative and flower buds, flowers, fruits and seeds. The nitrogen content in these organs changes noticeably during the growing season. So, in the spring (in initial period growth) in leaves and shoots it is increased. The source of nitrogen during this period is the reserves deposited in the plant in the fall. Then the amount of nitrogen decreases significantly. By autumn, the nitrogen content increases again and it flows into wintering organs.
A long-term lack of nitrogen leads to starvation of plants, which is reflected in the suspension of the growth of shoots and roots, the formation of smaller and paler leaves, and the shedding of fruits and berries. A sufficient amount of nitrogen ensures active growth of shoots, the formation of large dark green leaves, earlier entry of plants into fruiting, intensive flowering and increased fruit set.
Excess nitrogen with a lack of phosphorus and potassium in the soil can negatively affect the development of young plants. In this case, there is a delay in the growth of annual shoots and a later onset of a period of relative dormancy. In fruit-bearing trees, excess nitrogen causes insufficient ripening of fruits, their pale color, a decrease in sugar content and keeping quality, and a decrease in winter hardiness and frost resistance of fruit trees.
Nitrogen enters plants mainly through the roots from the soil, where it accumulates as a result of the introduction of organic and mineral fertilizers, as well as due to the activity of bacteria that fix it from the air.
Phosphorus compounds provide intermediate reactions associated with photosynthesis and plant respiration. Phosphorus is part of complex proteins. Its deficiency weakens the growth of shoots, branching of roots, and the formation of flower buds. Phosphorus in soil can be in the form of organic and mineral compounds. In the process of decomposition organic compounds it mineralizes and becomes available to plant roots. Most of the mineral phosphorus compounds are sparingly soluble and inaccessible to plants. U different breeds fruit assimilation capacity of roots is different. The roots of an apple tree, for example, absorb phosphorus from sparingly soluble compounds better than the roots of strawberries, currants, and gooseberries.
Potassium promotes the assimilation of carbon dioxide, the absorption of water by the plant, and metabolism. It ensures normal division of cells and tissues, growth of shoots and roots, formation of leaves and fruits, and increases the frost resistance of plants. Its deficiency leads to a change in the color of the leaves - their edges first turn yellow and then become covered with brown spots. In soil, potassium is found in organic and mineral compounds. Sandy soils are poor in potassium. Its main source is organic forms after their mineralization.
As for other macroelements, they are found in garden soils in quantities sufficient for plants.
Iron plays an important role in the formation of chlorophyll. If there is a deficiency of it, plants develop chlorosis (light yellow and even white leaves are formed).
Magnesium is part of chlorophyll. Its deficiency causes stunting of shoot growth, chlorosis or brown spotting, premature death and falling of leaves.
Zinc - component a number of vital enzymes, it influences the formation of growth substances (auxins) and plays an important role in redox processes in plants. If it is deficient, apple trees develop rosettes (instead of normal side shoots, they form rosettes with small deformed leaves).
Since these and other elements are needed by plants in small quantities, their needs are almost always met by the reserves that are available in the soil. An acute lack of microelements can be eliminated by adding them directly to the soil or spraying plants (foliar feeding).
- The importance of fruits and vegetables in human nutrition
Vegetables have great importance in human nutrition. Eating right means correctly combining plant and animal foods in accordance with age, nature of work, and state of health. When we eat meat, fats, eggs, bread, cheese, acidic acids are formed in the body inorganic compounds. To neutralize them, you need basic, or alkaline, salts, which are rich in vegetables and potatoes. Green vegetables contain the largest amount of acid neutralizing compounds.
Consumption of vegetables helps prevent many serious diseases and increases human tone and performance. In many countries of the world during treatment various diseases dietary nutrition fresh vegetables occupy a leading position. They are rich ascorbic acid(vitamin C), which ensures normal carbohydrate metabolism and promotes the removal of toxic substances from the body, resistance to many diseases, and reduction of fatigue. Many vegetables contain B vitamins, which affect human performance. Vitamins A, E, K, PP ( a nicotinic acid) are present in green peas, cauliflower and green vegetables. Cabbage contains vitamin and, which prevents the development peptic ulcer duodenum.
Organic acids, essential oils and vegetable enzymes improve the absorption of proteins and fats, enhance the secretion of juices, and promote digestion. Onions, garlic, horseradish, and radishes contain phytoncides that have bactericidal properties (they destroy pathogens). Tomatoes, peppers, and leaf parsley are rich in phytoncides. Almost all vegetables are suppliers of ballast substances - fiber and pectin, which improve intestinal function, help eliminate excess cholesterol from the body and harmful products digestion. Some vegetables, such as cucumber, have low nutritional value, but due to the content of proteolytic enzymes, they have a positive effect on metabolism when consumed. Green vegetables are of particular value. In their fresh form, they are not only better and more fully absorbed by humans, but also help (with enzymes) in the digestion of meat and fish in the body. At the same time, when cooked, green vegetables lose a significant part of their beneficial properties.
To meet the need for vitamins, carbohydrates, proteins, acids, salts, an adult needs to consume more than 700 g (37%) of food of animal origin and more than 1200 g (63%) of plant origin, including 400 g of vegetables, daily. The annual need for vegetables per person varies depending on the region of the country and is 126-146 kg, including cabbage various types 35--55 kg, tomatoes 25--32, cucumbers 10--13, carrots 6--10, beets 5--10, onions 6--10, eggplants 2--5, sweet peppers 1--3, green peas 5--8, melons 20--30, other vegetables 3--7.
Vegetables increase the digestibility of proteins, fats, and minerals. Added to protein foods and cereals, they enhance the secretory effect of the latter, and when consumed together with fat, they remove its inhibitory effect on gastric secretion. It is important to note that undiluted juices of vegetables and fruits reduce secretory function stomach, and diluted ones increase it.
The importance and role of vegetables in human nutrition is enormous, because they have a beneficial effect on digestion. However, you should not think that you need to eat only plant foods, as vegetarians believed. Modern science the basis healthy eating A person is nourished by a harmonious combination of plant and animal food.
According to scientists, the average daily norm vegetables for an adult is 300-400 g - 110-150 kg per year. The same amount of potatoes is needed.
The most important feature of vegetables is their high content of vitamins. This makes them indispensable in human nutrition.
Vitamins are special substances that regulate the vital functions of the body. More than 20 of them are now known. The most important vitamins for humans are vitamins A, B, Bi, B2, B12, C, D, E, K, and PP.
Vitamin A is found in animal products ( fish oil, cow butter), but its main amount enters the human body in the form of carotene when consuming tomatoes, lettuce, spinach, carrots, pumpkin, zucchini, cauliflower, and green leafy vegetables. In any case, this is an important action for any gardener.
Vitamin A promotes the growth of a young body, improves vision, and also enhances the activity of the endocrine glands. Its deficiency reduces the body's resistance various diseases, colds and causes eye disease (night blindness).
Vitamins Bi and Br are found in cabbage, tomatoes, potatoes, carrots, leafy vegetables and legumes. The first of them helps to improve cardiac activity and the nervous system, and the second - metabolic processes and the activity of the gastrointestinal tract. A lack of vitamin Bi in food can lead to muscle weakness and even paralysis of the legs.
Vitamin C is found in cabbage, tomatoes, peas, peppers, green onions, horseradish, lettuce, spinach, dill, parsley, potatoes and many other vegetables. This vitamin protects the body from many diseases (scurvy), accelerates the healing of wounds, fractures, improves the absorption of carbohydrates, proteins and fats, promotes normal liver function, recovery from pneumonia, diphtheria and whooping cough. The reserves of vitamin C in our body are insignificant. Therefore, we should consume fresh or canned vegetables throughout the year. Fresh greens are especially useful in winter.
Vitamin B is found in onions, spinach, green peas, rhubarb and other vegetables. This vitamin favors proper development bones and teeth in young body. In its absence, rickets develops and muscles weaken.
Vitamin E is found in all green parts of vegetables and especially in leafy ones. It helps improve the functioning of the nervous system, treat cardiovascular diseases and takes part in fat metabolism.
Vitamin K is found mainly in leafy vegetables, tomatoes and carrots; it promotes blood clotting and accelerates wound healing.
Vitamin PP is found in large quantities in cauliflower, tomatoes and carrots, takes part in the metabolism of carbohydrates and proteins, regulates the activity of the nervous system and prevents gout.
With a lack of vitamins, the normal functioning of the body is disrupted, and general weakness begins due to lack of appetite; all this leads to serious illnesses. In addition, when eating bread, meat, fish, butter, cheese, eggs in digestive organs harmful acids are formed. To neutralize them, you need to eat vegetables, which, in addition to vitamins, also contain mineral salts.
Some vegetables (onions, garlic, horseradish) contain special substances - phytoncides, which have an inhibitory effect on bacteria and thereby disinfect the digestive organs.
The importance of vegetable dishes in nutrition
The importance of vegetable dishes and side dishes in nutrition is determined primarily chemical composition vegetables and, first of all, carbohydrate content. Thus, potato dishes and side dishes serve as the most important source of starch. Dishes made from beets, carrots, and green peas contain a significant amount of sugars.
Vegetable dishes and side dishes are especially important as a source of valuable minerals. Most vegetables are dominated by alkaline ash elements (potassium, sodium, calcium, etc.), so dishes made from them help maintain acid-base balance in the body, since acidic elements predominate in meat, fish, cereals, and legumes. In addition, the ratio of calcium and phosphorus in many vegetables is close to optimal. Vegetable dishes, especially beets, are a source of hematopoietic microelements (copper, manganese, zinc, cobalt).
Although vitamins are partially lost during heat treatment, vegetable dishes and side dishes cover the bulk of the body's need for vitamin C and a significant portion for B vitamins. Parsley, dill, and onion, which are added when serving, significantly increases the C-vitamin activity of dishes.
Despite the low content and inferiority of most plant proteins, vegetable dishes serve as an additional source of them. When vegetables are cooked together with meat, fish, eggs, cottage cheese and other protein products, the secretion of gastric juice almost doubles and the absorption of animal proteins improves.
Flavoring, coloring and aromatic substances contained in vegetables help increase appetite and allow you to diversify your diet.
Vegetables are used to prepare dishes for self-serving in the breakfast, lunch or dinner diet and side dishes for meat and fish dishes.
Depending on the type of heat treatment, there are boiled, poached, fried, stewed, and baked vegetable dishes.
Vegetable side dishes can be simple or complex. Simple side dishes consist of one type of vegetable, and complex ones consist of several. For complex side dishes, vegetables are selected so that they combine well in taste and color. You can balance it out with a side dish. nutritional value food as a whole, regulate its weight and volume.
Meat dishes are usually served with side dishes of any vegetables. At the same time, side dishes with a delicate taste are more suitable for dishes made from lean meat: boiled potatoes, mashed potatoes, vegetables in milk sauce. It is better to serve dishes of fatty meat and poultry with more spicy side dishes - stewed cabbage, vegetables stewed with tomato sauce. Green peas, boiled potatoes, and mashed potatoes are served as a side dish for boiled meat. For fried meat - fried potatoes, complex side dishes. For boiled and poached fish - boiled potatoes, mashed potatoes. Side dishes of cabbage, rutabaga, and turnips are usually not served with fish dishes.
Processes that occur during heat treatment of vegetables
When vegetables are cooked, profound physical and chemical changes occur. Some of them play a positive role (softening vegetables, gelatinization of starch, etc.), improve the appearance of dishes (formation of a golden brown crust when frying potatoes); other processes reduce nutritional value (loss of vitamins, minerals
etc.), cause color changes, etc. The culinary specialist must be able to manage the processes taking place.
Softening of vegetables during heat treatment. Parenchyma tissue consists of cells covered with cell membranes. Individual cells are connected to each other by median plates. Cell walls and medial plates give vegetables mechanical strength. The composition of cell walls includes: fiber (cellulose), semi-fiber (hemicellulose), protopectin, pectin and connective tissue protein extensin. In this case, protopectin predominates in the middle plates.
During heat treatment, fiber remains virtually unchanged. Hemicellulose fibers swell but remain intact. The softening of the tissue is due to the breakdown of protopectin and extensin.
Protopectin - a polymer of pectin - has a complex branched structure. The main chains of its molecules consist of residues of galacturonic and polygalacturonic acids and the sugar rhamnose. The chains of galacturonic acids are connected to each other using various bonds (hydrogen, ether, anhydride, salt bridges), among which salt bridges of divalent calcium and magnesium ions predominate. When heated, an ion exchange reaction occurs in the middle plates: calcium and magnesium ions are replaced by monovalent sodium and potassium ions.
... GK - GK - GK ... ... GK - GK - GK ...
COO COONa
Ca+2Na+(K)+Ca++
... GK - GK - GK ... ... GK - GK - GK ...
In this case, the connection between the individual chains of galacturonic acids is destroyed. Protopectin breaks down and is formed
pectin is soluble in water, and the vegetable tissue softens. This reaction is reversible. For it to pass, in right side, it is necessary to remove calcium ions from the reaction sphere. Plant products contain phytin and a number of other substances that bind calcium. However, the binding of calcium (magnesium) ions does not occur in an acidic environment, so the softening of vegetables slows down. In hard water containing calcium and magnesium ions, this process will also take place slowly. As the temperature rises, the softening of vegetables accelerates.
In different vegetables, the rate of protopectin breakdown is not the same. Therefore, you can boil all vegetables, and fry only those in which protopectin has time to turn into pectin before all the moisture has evaporated (potatoes, zucchini, tomatoes, pumpkin). In carrots, turnips, rutabaga and some other vegetables, protopectin is so stable that they begin to burn before they reach culinary readiness.
The softening of vegetables is associated not only with the breakdown of protopectin, but also with the hydrolysis of extensin. Its content decreases significantly when vegetables are cooked. Thus, upon reaching culinary readiness, about 70% of the extensin in beets breaks down, and about 40% in parsley.
Change in starch. During heat treatment of potatoes, starch grains (Fig. III.9) located inside the cells are gelatinized due to cell sap. In this case, the cells are not destroyed and the paste remains inside them. In hot potatoes, the connection between individual cells is weakened due to the breakdown of protopectin and extensin, so when rubbed they are easily separated from each other, the cells remain intact, the paste does not leak out, and the puree turns out fluffy.
When cooled, the connection between the cells is partially restored, they are separated from each other with great difficulty, their shells tear when rubbed, the paste flows out, and the puree turns out sticky.
When frying potatoes and other starchy vegetables, the surface of the cut pieces quickly dehydrates, the temperature in it rises above 120°C, and the starch
Rice. III.9. Starch grains in potatoes:
1 - cheese; 2 - boiled; 3 - pureed after cooling
it breaks down to form pyrodextrins, which are brown in color, and the product becomes covered with a golden brown crust.
Change in sugars. When cooking vegetables (carrots, beets, etc.), part of the sugars (di- and monosaccharides) goes into the broth. When frying vegetables, baking onions, carrots for broths, caramelization of the sugars contained in them occurs. As a result of caramelization, the amount of sugar in vegetables decreases, and a golden brown crust appears on the surface. The reaction of melanoidin formation, accompanied by the appearance of dark-colored compounds - melanoidins, also plays an important role in the formation of a crispy crust on vegetables.
Change in color of vegetables during heat treatment. The different colors of vegetables are caused by pigments (coloring substances). When cooked, the color of many vegetables changes.
The color of beets is determined by pigments - betanins (red pigments) and betaxanthins (yellow pigments). The color shades of root vegetables depend on the content and ratio of these pigments. Yellow pigments are almost completely destroyed when beets are cooked, and red pigments partially (12-13%) pass into the decoction and are partially hydrolyzed. In total, about 50% of betanins are destroyed during cooking, as a result of which the color of root vegetables becomes less intense. The degree of change in beet color depends on a number of factors: heating temperature, betanin concentration, pH of the medium, contact with atmospheric oxygen, the presence of metal ions in the cooking medium, etc. The higher the heating temperature, the faster the red pigment is destroyed. The higher the concentration of betanin, the better it is preserved. Therefore, it is recommended to boil beets in their peels or stew them with a small amount of liquid. In an acidic environment, betanin is more stable, so vinegar is added when cooking or stewing beets.
Vegetables with a white color (potatoes, white cabbage, onions, etc.) acquire a yellowish tint when cooked. This is explained by the fact that they contain phenolic compounds - flavonoids, which form glycosides with sugars. During heat treatment, glycosides are hydrolyzed to release an aglycone, which is yellow in color.
The orange and red color of vegetables is due to the presence of carotenoid pigments: carotenes - in carrots, radishes; lycopenes - in tomatoes; violaxanthin - in pumpkin. Carotenoids are stable during heat treatment. They are insoluble in water, but highly soluble in fats; this is the basis for the process of extracting them with fat when sautéing carrots and tomatoes.
The pigment chlorophyll gives vegetables their green color. It is found in chloroplasts enclosed in the cytoplasm. During heat treatment, cytoplasmic proteins coagulate, chloroplasts are released and the acids of the cell sap interact with chlorophyll. As a result, pheophytin is formed - a brown substance. To preserve the green color of vegetables, a number of rules should be followed:
* boil them in a large amount of water to reduce the concentration of acids;
* do not cover the dish with a lid to facilitate removal with steam volatile acids;
* reduce the cooking time of vegetables by immersing them in boiling liquid and not overcooking them.
In the presence of copper ions in the cooking medium, chlorophyll acquires a bright green color; iron ions - brown; tin and aluminum ions - gray.
When heated in alkaline environment chlorophyll, when saponified, forms chlorophyllin, a bright green substance. The production of green dye is based on this property of chlorophyll: any greens (tops, parsley, etc.) are crushed and boiled with the addition of baking soda and squeeze the chlorophyllin paste through the cloth.
Changes in vitamin activity in vegetables. During heat treatment, vitamins undergo significant changes.
Vitamin C. Vegetables are the main source of vitamin C in human nutrition. It is highly soluble in water and very unstable when heat treated. Contained in vegetable cells in three forms: reduced (ascorbic acid), oxidized (dehydroascorbic acid) and bound (ascorbigen). Reduced and oxidized forms of vitamin C can easily transform into one another under the action of enzymes (ascorbinase - into the oxidized form, ascorbine reductase - into the reduced form). Dehydroascorbic acid is not inferior in biological value to ascorbic acid, but is much more easily destroyed during heat treatment. Therefore, during culinary processing, they try to inactivate ascorbinase, in particular, by immersing vegetables in boiling water.
Oxidation of vitamin C occurs in the presence of oxygen. The intensity of the process depends on the heating temperature of the vegetables and the duration of heat treatment. To reduce contact with oxygen, vegetables are cooked with the lid closed (except for green-colored vegetables); the volume of the container must correspond to the weight of the vegetables being boiled; in case of boiling, do not add cold, unboiled water. The faster vegetables are heated during cooking, the less ascorbic acid is destroyed. So, when immersing potatoes in cold water(during cooking) 35% of vitamin C is destroyed, when hot, only 7%. The longer the heating, the higher the degree of oxidation of vitamin C. Therefore, overcooking of food, long-term storage of food is not allowed, and reheating of ready-made dishes is undesirable.
Metal ions entering the cooking medium with tap water and from the walls of the cookware are catalysts for the oxidation of vitamin C. Copper ions have the greatest catalytic effect. In an acidic environment, this effect is less pronounced, so you should not add soda to speed up the cooking of vegetables.
Some substances contained in food products pass into the decoction and have a stabilizing effect on vitamin C. These substances include proteins, amino acids, starch, vitamins A, E, B 1, pigments - flavones, anthocyanins, carotenoids. For example, when boiling potatoes in water, the loss of vitamin C is about 30%, and when cooking in meat broth, vitamin C is almost completely preserved.
The more total of ascorbic acid in the product, the better the C-vitamin activity is preserved. This explains the fact that vitamin C in potatoes and cabbage is preserved better during the cooking process in the fall than in the spring. For example, when cooking unpeeled potatoes in the fall, the degree of destruction of vitamin C does not exceed 10%, in the spring it reaches 25%.
