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реферат Химический состав плодов и овощей и его изменения при созревании, хранении и переработке


Тип работы: реферат. Добавлен: 17.05.2012. Сдан: 2011. Страниц: 20. Уникальность по antiplagiat.ru: < 30%

Описание (план):

Министерство  образования Республики Беларусь
УО «Могилевский Государственный Университет Продовольствия» 

Кафедра иностранных языков 

для сдачи  кандидатского экзамена по английскому  языку на тему: 

     Chemical composition of fruits and vegetables and its CHANGES UNDER ripening, storage and processing 

химический  состав плодов и овощей и его изменения  при созревании, хранении и переработке 



     fruits, vegetables chemical composition, water, mineral substances, carbohydrates, organic acids, vitamins, flavonoids, ripeness, storage, processing 

     The results of the studies of chemical composition of  fruits and vegetables are given in this work. The results have demonstrated that fruits and vegetables have high carbohydrates, phenolic compounds, minerals and certain vitamins, especially vitamins A and C. However have low protein and fat content.
      During maturing, storage and processing occur changes of a chemical compound of raw material. One of the principal responsibilities of the food scientist and food technologist is to preserve food nutrients through all phases of food acquisition, processing, storage, and preparation. 


     плоды, овощи, химический состав, вода, минеральные  вещества, углеводы, органические кислоты, витамины, флавоноиды, созревание, хранение, переработка 

     В данной работе приведены результаты исследований химического состава  плодов и овощей. Результаты показывают, что плоды и овощи имеют  высокое содержание углеводов, фенольных  и минеральных соединений, а так же некоторых витаминной, особенно витаминов А и С. Однако имеют низкое содержание белка и жира.
     В процессе созревания, хранения и переработки  происходят изменения химического  состава сырья. Одной из основных задач ученого-диетолога и технолога является сохранение питательных веществ пищи на протяжении всех стадий сбора, обработки, хранения, и подготовки продовольствия. 


     Contents / содержание 


     Compositions of vegetables and fruit not only vary for a given kind in according to botanical variety, cultivation practices, and weather, but change with the degree of maturity prior to harvest, and the condition of ripeness, which is progressive after harvest and is further influenced by storage conditions.
     Most fresh vegetables and fruit are high in water content, low in protein, and low in fat. In these cases water contents will generally be greater than 70% and frequently greater than 85%.
     Commonly protein content will not be greater than 3.5% or fat content greater than 0.5 %. Exceptions exist in the case of dates and raisins which are substantially lower in moisture but cannot be considered fresh in the same sense as other fruit. Legumes such as peas and certain beans are higher in protein; a few vegetables such as sweet corn which are slightly higher in fat and avocados which are substantially higher in fat.
     Vegetables and fruit are important sources of both digestible and indigestible carbohydrates. The digestible carbohydrates are present largely in the form of sugars and starches while indigestible cellulose provides roughage which is important to normal digestion.
     Fruit and vegetables are also important sources of minerals and certain vitamins, especially vitamins A and C. The precursors of vitamin A, including beta-carotene and certain other carotenoids, are to be found particularly in the yellow-orange fruit and vegetables and in the green leafy vegetables.
     Citrus fruit are excellent sources of vitamin C, as are green leafy vegetables and tomatoes. Potatoes also provide an important source of vitamin C for the diets of many countries. This is not so much due to the level of vitamin C in potatoes which is not especially high but rather to the large quantities of potatoes consumed. 

      1 Chemical composition

      1.1 Water

     Vegetal cells contain important quantities of water. Water plays a vital role in the evolution and reproduction cycle and in physiological processes. It has effects on the storage period length and on the consumption of tissue reserve substances.
     In vegetal cells, water is present in following forms:
    bound water or dilution water which is present in the cell and forms true solutions with mineral or organic substances;
    colloidal bound water which is present in the membrane, cytoplasm and nucleus and acts as a swelling agent for these colloidal structure substances; it is very difficult to remove during drying/dehydration processes;
    constitution water, directly bound on the chemical component molecules and which is also removed with difficulty.
     Vegetables contain generally 90-96% water while for fruit normal water content is between 80 and 90%.

      1.2 Mineral substances

     Mineral substances are present as salts of organic or inorganic acids or as complex organic combinations (chlorophyll, lecithin, etc.); they are in many cases dissolved in cellular juice.
     Vegetables are more rich in mineral substances as compared with fruits. The mineral substance content is normally between 0.60 and 1.80% and more than 60 elements are present; the major elements are: K, Na, Ca, Mg, Fe, Mn, Al, P. Cl, S.
     Among the vegetables which are especially rich in mineral substances are: spinach, carrots, cabbage and tomatoes. Mineral rich fruit includes: strawberries, cherries, peaches and raspberries. Important quantities of potassium (K) and absence of sodium chloride (NaCl) give a high dietetic value to fruit and to their processed products. Phosphorus is supplied mainly by vegetables.
     Vegetables usually contain more calcium than fruit; green beans, cabbage, onions and beans contain more than 0.1% calcium. The calcium/phosphorus or Ca/P ratio is essential for calcium fixation in the human body; this value is considered normal at 0.7 for adults and at 1.0 for children. Some fruit are important for their Ca/P ratio above 1.0: pears, lemons, oranges and some temperate climate mountain fruits and wild berries.
     Even if its content in the human body is very low, iron (Fe) has an important role as a constituent of haemoglobin. Main iron sources are apples and spinach.
     Salts from fruit have a basic reaction; for this reason fruit consumption facilitates the neutralisation of noxious uric acid reactions and contributes to the acid-basic equilibrium in the blood.

      1.3 Carbohydrates

     Carbohydrates are the main component of fruit and vegetables and represent more than 90% of their dry matter. From an energy point of view carbohydrates represent the most valuable of the food components; daily adult intake should contain about 500 g carbohydrates.
     Carbohydrates play a major role in biological systems and in foods. They are produced by the process of photosynthesis in green plants. They may serve as structural components as in the case of cellulose; they may be stored as energy reserves as in the case of starch in plants; they may function as essential components of nucleic acids as in the case of ribose; and as components of vitamins such as ribose and riboflavin.
     Carbohydrates can be oxidised to furnish energy, and glucose in the blood is a ready source of energy for the human body. Fermentation of carbohydrates by yeast and other microorganisms can yield carbon dioxide, alcohol, organic acids and other compounds.
     Some properties of sugars. Sugars such as glucose, fructose, maltose and sucrose all share the following characteristics in varying degrees, related to fruit and vegetable technology:
    they supply energy for nutrition;
    they are readily fermented by micro-organisms;
    in high concentrations they prevent the growth of micro-organisms, so they may be used as a preservative;
    on heating they darken in colour or caramelise;
    some of them combine with proteins to give dark colours known as the browning reaction.
     Some properties of starches:
    They provide a reserve energy source in plants and supply energy in nutrition;
    they occur in seeds and tubers as characteristic starch granules.
     Some properties of celluloses and hemicelluloses:
    They are abundant in the plant kingdom and act primarily as supporting structures in the plant tissues;
    they are insoluble in cold and hot water;
    they are not digested by man and so do not yield energy for nutrition;
    the fibre in food which produces necessary roughage is largely cellulose.
     Some properties of pectins and carbohydrate gums.
    Pectins are common in fruits and vegetables and are gum-like (they are found in and between cell walls) and help hold the plant cells together;
    pectins in colloidal solution contribute to viscosity of the tomato paste;
    pectins in solution form gels when sugar and acid are added; this is the basis of jelly manufacture.

      1.4 Fats

     Generally fruit and vegetables contain very low level of fats, below 0.5%. However, significant quantities are found in nuts (55%), apricot kernel (40%), grapes seeds (16%), apple seeds (20%) and tomato seeds (18%).

      1.5 Organic acids

     Fruit contains natural acids, such as citric acid in oranges and lemons, malic acid of apples, and tartaric acid of grapes. These acids give the fruits tartness and slow down bacterial spoilage.
     We deliberately ferment some foods with desirable bacteria to produce acids and this give the food flavour and keeping quality. Examples are fermentation of cabbage to produce lactic acid and yield sauerkraut and fermentation of apple juice to produce first alcohol and then acetic acid to obtain vinegar.
     Organic acids influence the colour of foods since many plant pigments are natural pH indicators.
     With respect to bacterial spoilage, a most important contribution of organic acids is in lowering a food's pH. Under anaerobic conditions and slightly above a pH of 4.6, Clostridium botulinum can grow and produce lethal toxins. This hazard is absent from foods high in organic acids resulting in a pH of 4.6 and less.
     Acidity and sugars are two main elements which determine the taste of fruit. The sugar/acid ratio is very often used in order to give a technological characterisation of fruits and of some vegetables.

      1.6 Nitrogen-containing substances

     These substances are found in plants as different combinations: proteins, amino acids, amides, amines, nitrates, etc. Vegetables contain between 1.0 and 5.5 % while in fruit nitrogen-containing substances are less than 1% in most cases.
     Among nitrogen containing substances the most important are proteins; they have a colloidal structure and, by heating, their water solution above 50°C an one-way reaction makes them insoluble. This behaviour has to be taken into account in heat processing of fruits and vegetables.
     From a biological point of view vegetal proteins are less valuable then animal ones because in their composition all essential amino-acids are not present.

      1.7 Vitamins

     Vitamins are defined as organic materials which must be supplied to the human body in small amounts apart from the essential amino-acids or fatty acids.
     Vitamins function as enzyme systems which facilitate the metabolism of proteins, carbohydrates and fats but there is growing evidence that their roles in maintaining health may extend yet further.
     The vitamins are conveniently divided into two major groups, those that are fat-soluble and those that are water-soluble. Fat-soluble vitamins are A, D, E and K. Their absorption by the body depends upon the normal absorption of fat from the diet. Water-soluble vitamins include vitamin C and several members of the vitamin B complex.
     Vitamin A or Retinol.
     This vitamin is found as such only in animal materials - meat, milk, eggs and the like. Plants contain no vitamin A but contain its precursor, beta-carotene. Man needs either vitamin A or beta-carotene which he can easily convert to vitamin A. Beta-carotene is found in the orange and yellow vegetables as well as the green leafy vegetables, mainly carrots, squash, sweet potatoes, spinach and kale.
     A deficiency of vitamin A leads to night blindness, failure of normal bone and tooth development in the young and diseases of epithelial cells and membrane of the nose, throat and eyes which decrease the body's resistance to infection.
     Vitamin C.
     Vitamin C is the anti-scurvy vitamin. Lack of it causes fragile capillary walls, easy bleeding of the gums, loosening of teeth and bone joint diseases. It is necessary for the normal formation of the protein collagen, which is an important constituent of skin and connective tissue. Like vitamin E, vitamin C favours the absorption of iron.
     Vitamin C, also known as ascorbic acid, is easily destroyed by oxidation especially at high temperatures and is the vitamin most easily lost during processing, storage and cooking.
     Excellent sources of vitamin C are citrus fruits, tomatoes, cabbage and green peppers. Potatoes also are a fair source (although the content of vitamin C is relatively low) because we consume large quantities of potatoes.

      1.8 Enzymes

     Enzymes are biological catalysts that promote most of the biochemical reactions which occur in vegetable cells.
     Some properties of enzymes important in fruit and vegetable technology are the following:
    in living fruit and vegetables enzymes control the reactions associated with ripening;
    after harvest, unless destroyed by heat, chemicals or some other means, enzymes continue the ripening process, in many cases to the point of spoilage - such as soft melons or overripe bananas;
    because enzymes enter into a vast number of biochemical reactions in fruits and vegetable, they may be responsible for changes in flavour, colour, texture and nutritional properties;
    the heating processes in fruit and vegetables manufacturing/processing are designed not only to destroy micro-organisms but also to deactivate enzymes and so improve the fruit and vegetables' storage stability.
     Enzymes have an optimal temperature - around +50°C where their activity is at maximum. Heating beyond this optimal temperature deactivates the enzyme. Activity of each enzyme is also characterised by an optimal pH.
     In fruit and vegetable storage and processing the most important roles are played by the enzymes classes of hydrolases (lipase, invertase, tannase, chlorophylase, amylase, cellulase) and oxidoreductases (peroxidase, tyrosinase, catalase, ascorbinase, polyphenoloxidase).

      1.9 Sources of colour and colour changes

     The pigments and colour precursors of fruit and vegetables occur for the most part in the cellular plastic inclusions such as the chloroplasts and other chromoplasts, and to a lesser extent dissolved in fat droplets or water within the cell protoplast and vacuoles.
     These pigments are classified into four major groups which include the chlorophylls, carotenoids, anthocyanins, and anthoanthins. Pigments belonging to the latter two groups also are referred to as flavonoids, and include the tannins.
     The Chlorophylls. The chlorophylls are contained mainly within the chloroplasts and have a primary role in the photosynthetic production of carbohydrates from carbon dioxide and water. The bright green colour of leaves and other parts of plants is largely due to the oilsoluble chlorophylls, which in nature are bound to protein molecules in highly organised complexes.
     When the plant cells are killed by ageing, processing, or cooking, the protein of these complexes is denatured and the chlorophyll may be released. Such chlorophyll is highly unstable and rapidly changes in colour to olive green and brown. This colour change is believed to be due to the conversion of chlorophyll to the compound pheophytin.
     Conversion to pheophytin is favoured by acid pH but does not occur readily under alkaline conditions. For this reason peas, beans, spinach, and other green vegetables which tend to lose their bright green colours on heating can be largely protected against such colour changes by the addition of sodium bicarbonate or other alkali to the cooking or canning water.
     However, this practice is not looked upon favourably nor used commercially because alkaline pH also has a softening effect on cellulose and vegetable texture and also destroys vitamin C and thiamin at cooking temperatures.
     The Carotenoids. Pigments belonging to this group are fat-soluble and range in colour from yellow through orange to red. They often occur along with the chlorophylls in the chloroplasts, but also are present in other chromoplasts and may occur free in fat droplets. Important carotenoids include the orange carotenes of carrot, maize, apricot, peach, citrus fruits, and squash; the red lycopene of tomato, watermelon, and apricot; the yellow-orange xanthophyll of maize, peach, paprika and squash; and the yellow-orange crocetin of the spice saffron. These and other carotenoids seldom occur singly within plant cells.
     A major importance of some of the carotenoids is their relationship to vitamin A. A molecule of orange beta-carotene is converted into two molecules of colourless vitamin A in the animal body. Other carotenoids like alpha-carotene and gamma-carotene also are precursors of vitamin A, but because of minor differences in chemical structure one molecule of each of these yields only one molecule of vitamin A.
     In food processing the carotenoids are fairly resistant to heat, changes in pH, and water leaching since they are fat-soluble. However, they are very sensitive to oxidation, which results in both colour loss and destruction of vitamin A activity.
     The Flavonoids. Pigments and colour precursors belonging to this class are water-soluble and commonly are present in the juices of fruit and vegetables. The flavonoids include the purple, blue, and red anthocyanins of grapes, berries, plump, eggplant, and cherry; the yellow anthoxanthins of light coloured fruit and vegetables such as apple, onion, potato, and cauliflower, and the colourless catechins and leucoanthocyanins which are food tannins and are found in apples, grapes, tea, and other plant tissues. These colourless tannin compounds are easily converted to brown pigments upon reaction with metal ions.
     Properties of the anthocyanins include a shifting of colours with pH. Thus many of the anthocyanins which are violet or blue in alkaline media become red upon addition of acid.
     Cooking of beets with vinegar tends to shift the colour from a purplish red to a brighter red, while alkaline water can influence the colour of red fruits and vegetables toward violet and gray-blue.
     The anthocyanins also tend toward the violet and blue hues upon reaction with metal ions, which is one reason for lacquering the inside of metal cans when the true colour of anthocyanin-containing fruits and vegetables is to be preserved.
     The water-soluble property of anthocyanins also results in easy leaching of these pigments from cut fruit and vegetables during processing and cooking.
     The yellow anthoxanthins also are pH sensitive tending toward a deeper yellow in alkaline media. Thus potatoes or apples become somewhat yellow when cooked in water with a pH of 8 or higher, which is common in many areas. Acidification of the water to pH 6 or lower favours a whiter colour.
     The colourless tannin compounds upon reaction with metal ions form a range of dark coloured complexes which may be red, brown, green, grey, or black. The various shades of these coloured complexes depend upon the particular tannin, the specific metal ion, pH, concentration of the complex, and other factors not yet fully understood.
     Water-soluble tannins appear in the juices squeezed from grapes, apples, and other fruits as well as the brews from extraction of tea and coffee. The colour and clarity of tea are influenced by the hardness and pH of the brewing water. Alkaline waters that contain calcium and magnesium favour the formation of dark brown tannin complexes which precipitate when the tea is cooled.
     If acid in the form of lemon juice is added to such tea its colour lightens and the precipitate tends to dissolve. Iron from equipment or from pitted tin cans has caused a number of unexpected colours to develop in products containing tannins, such as coffee, cocoa and foods flavoured with these.
     The tannins are also important because they have an astringency which influences flavour and contributes body to such beverages as tea, wine, apple cider, etc.

      2 Changes of a chemical composition of fruits and vegetables under ripening and storage

     Fruit and vegetables are in a live state after harvest. Continued respiration gives off carbon dioxide, moisture, and heat which influence storage, packaging, and refrigeration requirements. Continued transpiration adds to moisture evolved and further influences packaging requirements.
     Further activities of fruit and vegetables, before and after harvest, include changes in carbohydrates, pectins, organic acids, and the effects these have on various quality attributes of the products.
     As for changes in carbohydrates, few generalizations can be given with respect to starches and sugars. In some plant products sugars quickly decrease and starch increases in amount soon after harvest. This is the case for ripe sweet corn which can suffer flavour and texture quality losses in a very few hours after harvest.
     Unripe fruit, in contrast, is frequently high in starch and low in sugars. Continued ripening after harvest generally results in a decrease in starch and a increase in sugars as in the case of apples and pears. However, this does not necessarily mean that the starch is the source of the newly formed sugars.
     Further, the courses of change in starch and sugars are markedly influenced by postharvest storage temperatures. Thus potatoes stored below about 10 C° (50 F°) continue to build up high levels of sugars, while the same potatoes stored above 10 C° do not.
     This property is used to help the dehydration process in potato storage. Here potatoes should have a low reducing sugar content so as to minimise Maillard browning reactions during drying and subsequent storage of the dried product. In this case potatoes are stored above 10°C prior to being further processed.
     After harvest the pectin changes in fruit and vegetables are more predictable. Generally there is decrease in water-insoluble pectic substance and a corresponding increase in watersoluble pectin. This contributes to the gradual softening of fruits and vegetables during storage and ripening. Further breakdown of water-soluble pectin by pectin methyl esterase also occurs.
     The organic acids of fruit generally decreases during storage and ripening. This occurs in apples and pears and is especially important in the case of oranges. Oranges have a long ripening period on the tree and time of picking is largely determined by degree of acidity and sugar content which have major effects upon juice quality.
     It is important to note that the reduction of acid content on ripening influences more than just the tartness of fruit. Since many of the plant pigments are sensitive to acid, fruit colour would be expected to change. Additionally, the viscosity of pectin gel is affected by acid and sugar contents, both of which change with ripening.

      3 Stability of nutrients under processing

     One of the principal responsibilities of the food scientist and food technologist is to preserve food nutrients through all phases of food acquisition, processing, storage, and preparation.
     This shows the stability of vitamins, essential amino acids, and minerals to acid, air, light, and heat, and gives an indication of possible cooking losses. Vitamin A is highly sensitive to acid, air, light and heat; vitamin C to alkalinity, air, light and heat; vitamin D to alkalinity, air, light and heat; thiamin to alkalinity, air, and heat in alkaline solutions; etc. Cooking losses of some essential nutrients may be in excess of 75%. In modern food processing operations, however, losses are seldom in excess of 25% .
     The ultimate nutritive value of a food results from the sum total of losses incurred throughout its history - from farmer to consumer. Nutrient value begins with genetics of the plant and animal. The farmland fertilization program affects tissue composition of plants, and animals consuming these plants. The weather and degree of maturity at harvest affect tissue composition.
     Storage conditions before processing affect vitamins and other nutrients. Washing, trimming, and heat treatments affect nutrient content. Canning, evaporating, drying, and freezing alter nutritional values, and the choices of times and temperatures in these operations frequently must be balanced between good bacterial destruction and minimum nutrient destruction.
     Packaging and subsequent storage affect nutrients. One of the most important factors is the final preparation of the food in the home and the restaurant - the steam table can destroy much of what has been preserved through all prior manipulations. 


     Состав  плодов и овощей изменяется не только в зависимости от ботанического  разнообразия, методов культивирования  и климатических условий, но и  согласно изменению степени зрелости до сбора урожая и состоянию зрелости, которая является прогрессивной после сбора урожая и далее влияет на условия хранения.
     Большинство свежих овощей и плодов имеют высокое  содержание воды и низкое содержание белка и жира. Таким образом,  содержание воды обычно более чем 70 %, а часто более чем 85 %.
     Обычно  содержание белка не более чем 3.5 % и содержание жира не более чем 0.5 %. Исключения составляют финики и изюм, которые имеют значительно меньшую влажность, но их нельзя счесть свежими в том же самом смысле, как и другие плоды. Бобовые типа гороха и некоторые бобы имеют более высокое содержание белка; некоторые овощи типа сладкой кукурузы, у которых содержание жира  немного выше и авокадо, в которых содержание жира значительно выше.  
     Овощи и плоды являются важными источниками  как легко усваиваемых, так и  трудно усваиваемых углеводов. Легко усваиваемые углеводы присутствуют в значительной степени в виде сахаров и крахмала, в то время как трудно усваиваемая целлюлоза обеспечивает грубую пищу, которая важна для нормального пищеварения.
     Плоды и овощи также являются важными  источниками минеральных веществ и некоторых витаминов, особенно витаминов А и C. Предшественники витамина A, включающие ?-каротин и некоторые другие каротиноиды, присутствуют особенно в желто-оранжевых плодах, овощах и в зеленых листовых овощах.
     Плоды цитрусовых являются превосходными источниками витамина C, как - зеленые листовые овощи и помидоры. Картофель также является важным источником витамина C для питания многих стран. Это обуславливается не столько уровнем витамина C в картофеле, содержание которого не достаточно высоко, а скорее благодаря большому количеству потребляемого картофеля. 

      1 Химический состав

      1.1 Вода

     Растительные  клетки содержат значительные количества воды. Вода играет важную роль в развитии, в цикле восстановления и в  физиологических процессах. Она влияет на продолжительность срока хранения.
     В растительных клетках, вода присутствует в следующих формах:
    связанная вода или вода растворенная, которая присутствует в клетке и формирует истинные растворы с минеральными или органическими веществами;
    коллоидная связанная вода, которая присутствует в мембране, цитоплазме и ядре и действует как набухающий агент для этих коллоидных структурных веществ; ее очень трудно удалить в течение процессов сушки/обезвоживания;
    вода, непосредственно связанная химическими составляющими молекул и которая также удаляется с трудом.
     Овощи, как правило,  содержат 90-96% воды, в то время как для плодов нормальное  содержание воды - между 80 и 90 %.

      1.2 Минеральные вещества

     Минеральные вещества присутствуют в виде солей органических или неорганических кислот или как сложные органические соединения (хлорофилл, лецитин, и т.д.); во многих случаях они растворены  в клеточном соке.
     Овощи более богаты минеральными веществами по сравнению с плодами. Содержание минеральных веществ обычно между 0.60 и 1.80% и присутствует более чем 60 элементов главные из которых: K, Na, Са, Мg, Fe, Мn, АI, P, CI, S.
     Среди овощей особенно богаты минеральными веществами: шпинат, морковь, капуста  и помидоры. Плодами, богатыми минеральными веществами являются земляника, вишня, персики и малина. Значительные количества калия (K) и отсутствие хлорида натрия (NaCl) способствуют высокой питательной ценности плодов и их переработанной продукции. Фосфор содержится главным образом в овощах.
     Овощи обычно содержат больше кальция, чем плоды; зеленые бобы, капуста, лук и бобы содержат кальция более чем 0.1 %. Отношение кальций/фосфор или Ca/P важно для закрепления кальция в человеческом организме; нормальным является соотношение 0.7 для взрослых и 1.0 для детей. Некоторые плоды важны благодаря соотношению Ca/P 1.0: груши, лимоны, апельсины, некоторые плоды умеренного климата и дикие ягоды.
     Даже  если его содержание в человеческом организме является очень низким, железо (Fe) имеет большое значение как составляющая гемоглобина. Главными  источниками железа являются яблоки и шпинат.
     Соли  плодов имеют основную реакцию; по этой причине потребление плодов облегчает  нейтрализацию вредных кислотных  реакций в моче и способствует кислотному равновесию в крови.

      1.3 Углеводы

     Углеводы  являются главным компонентом плодов и овощей и составляют более чем 90% от  сухого вещества. С точки  зрения энергии углеводы самые ценные из компонентов продовольствия; ежедневное потребление углеводов для взрослого  человека должно составлять приблизительно 500г.
     Углеводы  имеют большое значение в биологических  системах и в пищевых продуктах. Они получаются путем фотосинтеза  на зеленых растениях. Они могут  служить структурными компонентами, как в случае целлюлозы; они могут  являться источником энергии, как, например, крахмал в растениях; они могут функционировать как важные компоненты нуклеиновых кислот, как в случае рибозы; и как компоненты витаминов типа рибозы и рибофлавина.
     Углеводы  могут окисляться, чтобы давать энергию, а  глюкоза в крови является готовым источником энергии для человеческого организма. Сбраживание углеводов дрожжами или другими микроорганизмами может привести к выделению углекислого газа, спирта, органических кислот и других соединений.
     Некоторые свойства сахаров. Сахара типа глюкозы, фруктозы, мальтозы и сахарозы имеют следующие характеристики в различных степенях, связанных с технологией плодов и овощей:
      они снабжают пищу энергией;
      они легко сбраживаются микроорганизмами;
      в высоких концентрациях они предотвращают рост микроорганизмов, поэтому  могут использоваться как консервант;
      при нагревании они темнеют  и карамелизуются;
      некоторые из них соединяются с белками, темнеют, что известно как реакция Майера.
     Некоторые свойства крахмала:
      он обеспечивает запасом энергии растения и снабжает энергией пищу;
      он находятся в семенах и клубнях как характерные гранулы крахмала.
      Некоторые свойства целлюлозы и геммицеллюлозы:
      в большом количестве они встречаются в растениях и нужны, прежде всего, для поддержки структуры в тканях растения;
      они нерастворимы в холодной и горячей воде;
      они не усваиваются организмом и  не производят энергию для пищи;
      волокно в пище придает ей необходимую грубость, которое главным образом является целлюлозой.
     Некоторые свойства пектина.
      пектины распространены в плодах и овощах и имеют резиноподобную форму (они находятся между стенками клетки), и помогают скреплять ячейки растения;
      пектины в коллоидном растворе способствуют вязкости томатной пасты;
      пектины в растворе формируют гели при добавлении сахара и кислоты, что составляет основу производства желе.

      1.4 Жиры

     Как правило, плоды и овощи содержат очень мало жиров, менее 0.5%. Однако, значительные количества найдены в орехах (55 %), косточках абрикоса (40 %), семенах винограда (16 %), семенах яблок (20 %) и семенах томатов (18 %).

      1.5 Органические кислоты

     Плоды содержат натуральные кислоты, типа лимонной кислоты в апельсинах и  лимонах, яблочной кислоты в  яблоках и винная кислота в винограде. Эти кислоты дают резкость плодам и замедляют бактериальную порчу.
     Мы  преднамеренно сбраживаем некоторые  пищевые продукты с необходимыми бактериями, для получения кислоты, а это дает аромат пище и продлевается срок годности. Например,  квашение капусты, для получения молочной кислоты и производство кислой капусты, и брожение яблочного сока, чтобы получить первичный спирт, а затем уксусную кислоту, для получения уксуса.
     Органические  кислоты влияют на цвет пищевых продуктов, так как многие пигменты растения являются естественными pH индикаторами.
     Самый важный вклад органических кислот относительно бактериальной порчи, заключается  в снижении pH продуктов. При анаэробных условиях и pH немного выше 4.6, Clostridium botulinum может увеличиваться и произвести смертельные токсины. Эта опасность отсутствует в пищевых продуктах с высоким содержанием органических кислот, с pH 4.6 и меньше.
и т.д.................

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