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Production of marmalade-Pastila products

Pectin plant the role of pectin in plants

A leading role in the production of marmalade-Pastila products plays studneobrazovaniya process, which depends on a kind of structure, marmalade and pastilles.

The process of gelation is determined primarily by the properties of pectic substances that are part of the processed fruit and berry raw materials. Therefore, knowledge of the physico-chemical properties of pectic substances, their composition and structure is the key to understanding the technology of this group of industries.

Pectic substances are an integral part of plant tissue. The substance of the cell walls of the latter consists of cellulose in the layer facing the protoplasm. Towards the outer layer, the cellulose passes into hemicellulose. In the outer layer of the cell walls the binder is deposited, which is partially located in the intercellular spaces, forming the median plates of plant tissue. This substance is called pectin (from the Greek word rektos - jelly-like, coagulated), as it has the ability to form jelly.

Thus, the fruit tissue is composed of individual cells or cell fibers interconnected natural cementing solution

The role of the cement in this case performs the pectin or rather, pectin, since we are dealing here with a mixture of substances.

It would, however, be wrong to imagine the pectic substances of the fruit only as binders, since, in addition to their presence in the cell walls and in the intercellular spaces, a certain amount of pectic substances are often found in the dissolved form and in the cell sap (especially in mature fruits).

Pectic substances are found in both green and non-chlorophyll parts of plants: in the leaves and fruits of trees and bushes, in the foliage and in fleshy thickenings of root crops. There are indications of their presence in the cambial layer of young trees.

Pectic substances play a role in the metabolism of plant tissue. They have the ability to bind water and swell. Therefore, their purpose in plants is also in the fact that they are one of the carriers of the water supply. The binding of water to pectin substances limits the development of enzymatic and chemical processes in fruit tissue. Pectic substances contribute to the retention of water in various organs of the plant, protecting them from drying out. These properties of pectic substances, for example, determine to a large extent the “keeping quality” of fruits and berries, i.e., their ability for long-term storage after harvest.

In the processing of plant materials, pectic substances play an important role: sometimes positive - in the production processes of withering tea leaves, tobacco fermentation; sometimes negative, for example, in the production of fruit and berry juices, in the processing of flax, the diffusion of sugar beet, etc., where pectin substances are undesirable cellulose satellites in the fibers or act as mute-forming or pathogen-forming agents.

Most researchers describe pectic substances as decay products of cellulose and hemicellulose.

Pectic substances in plants are in a state of constant change. They continuously change their chemical composition and physical properties in the process of plant development, fruit growth and ripening, moving from one form to another.

Protopectin and its hydrolysis

Protopectin is the forerunner of "true" pectins in plants. In the fruits of immature or in the period of growth, pectic substances are contained mainly in the form of protopectin. Under this name, cold water-insoluble pectin substance is included in the composition of the material of the cell walls and middle plates, in contrast to the dissolved, so-called free pectin, which is part of the cell juice of ripe fruits. The name “protopectin” is explained by the fact that this substance is considered as the initial, initial form of pectic substances.

In its pure form, protopectin has not yet been isolated, since, using currently known methods for isolating pectic substances, we always obtain partially hydrolyzed protopectin along with the products of its hydrolysis.

Like cellulose, protopectin is insoluble in cold water, but unlike cellulose it is easily hydrolyzed with hot water and does not dissolve in Schweitzer's reagent (a solvent for cellulose). It does not have the ability to gelation, which is characteristic only of some products of its shallow hydrolysis.

The hydrolysis of protopectin in water begins with a temperature of 80-85 °. At the same time, protopectin is split into soluble pectin substance (this substance is pectin itself) and cellulose.

When protopectin is treated with weak solutions of acids and alkalis, acid or alkaline hydrolysis of propectin occurs. As a result of such hydrolysis, a mixture of dissolved pectic substances is also obtained, whose composition does not coincide with the composition of pectin obtained as a result of hydrolysis with hot water.

On the composition and structure of protopectin at the present time there is still no consensus. Chemical and microscopic studies of a number of authors lead to the assumption that protopectin is a combination of pectin with cellulose, being like an intermediate form between these substances.

Studies of botanists using x-rays and color reactions have established that the protopectin of plant tissue, especially its variety, which is found in the intercellular spaces, consists mainly of insoluble calcium polygalacturonates or of calcium and magnesium salts of pectin and pectic acids (pectinates and pectates of calcium and magnesium Mg).

The hardness of the immature fruits is explained by the presence of protopectin in them. The natural hydrolysis of protopectin occurs in living plant tissue mainly under the action of enzymes. This process is similar to that described above thermal hydrolysis. It is assumed that the enzyme protopectinase acts in this case.

There are indications that the natural transformations of protopectin develop under the action of hydrogen peroxide, which is formed in the tissue of the fruit. The formation of peroxide is catalyzed by dehydrogenases present in plant tissue. This hypothesis has not been fully confirmed.

Equally important for the flow of natural hydrolysis of protopectin is the action of sunlight (thermal and chemical) and the action of the acids contained in the fruit. The more the fruit is exposed to sunlight and the higher the acidity of the fruit, the more intense is the natural hydrolysis of protopectin, as well as the further disintegration of pectic substances.

Protopectin hydrolysis is most studied in fruits. This process, which occurs in fresh fruits, causes those external changes that characterize the ripening of fruits.

As the protopectin passes into soluble pectin, the pulp cells, which were previously firmly glued together, are surrounded by a more tender gelatinous mass of soluble pectin. Fruits gradually become softer, due to the separation of tissue cells, pulp loosening characteristic of fruit ripening occurs. This process is the opposite of the fruit growth process. During the growth period, the green fruits, as well as other green parts of the plant, perform known constructive functions (the phenomenon of photosynthesis, etc.). The process of maturation is mainly the process of destruction of the fetus, in which the phenomena of the breakdown of the original substance (splitting of carbohydrates, acids, etc.) prevail. The hydrolysis of pectic substances is one of the most striking manifestations of this decay.

What has been said above applies mainly to fruits or parts of plants that are exposed to sunlight (fruits of trees and shrubs, sunflower baskets). Pectic substances of root crops (beets, carrots, etc.) are not exposed to acids and direct sunlight, therefore their hydrolysis in the plant tissue develops much slower and an insoluble protopectin fraction dominates in their composition.

The composition of pectin. The structure of the pectin molecule

Due to the difficulty of isolating pectic substances in a pure form, until recently there was a number of ambiguities and contradictions regarding their chemical composition.

The evolution of views on this issue can now be briefly presented in the following form.

Early studies have shown the presence in the pectin complex Araban and galactan.

In the study of ash pectin (protopectin) was found to be in the bulk is made up of calcium and magnesium, with a predominance of calcium.

It was also shown that when treating pectin with caustic soda, the methoxyl groups of CH30 are cleaved. In this solution, the sodium salt of the organic acid pectin and methyl alcohol is obtained (saponification of pectin occurs). The same effect as caustic soda on pectin have other alkalis and alkaline-reactive substances. After complete pectin saponification with alkali and after the removal of metal ions from the resulting salt, free acid remains, which was originally called pectic acid.

It was concluded on the basis of these observations is that the pectin methyl ester pectin acid.

In the future, in connection with the discovery of pectin substances of Arabian, calcium and magnesium, it was suggested that they represent a mixture of arabane with a calcium-magnesium salt of pectic acid.

Both of these components differ from each other in their chemical and physical properties. So, for example, araban is levogyrate, while the rest of the complex is dextrorotatory. Araban is soluble in alcohol, while the calcium-magnesium salt of pectinic acid is insoluble in it. The latter property was used to araban's revenge from the main pectin complex. Araban is extracted from pectin by long-term treatment of the latter with 70% alcohol. In this case, the calcium-magnesium gall of pectic acid remains in the sediment. The addition of HCl to alcohol in the extraction of araban achieves the removal of Ca and Mg from this salt. The insoluble residue thus obtained was regarded as pectic acid.

Subsequently, a crystalline substance, similar in its properties to galactose and glucuronic acid, was isolated from the alcohol-insoluble part of the pectin complex. This substance, which constitutes the bulk of the pectin, was identified as galacturonic acid.16.1

Galacturonic acid is an aldehydic acid, which is obtained by careful oxidation of galactose in the same way as the same oxidation of glucose from the latter produces its isomer, glucuronic acid.

Galacturonic acid under the action of acid when heated cleaves CO2 and forming furfural.

Initially, it was believed that galacturonic acid forms the basis of the pectin complex in the form of a polymerized molecule of stragalacturonic acid.

Last incorporates 4 molecules d-galacturonic acid, which is taken away from the 4 water molecules.16.2

It was assumed that tetragalacturonic acid, which forms the core of the pectin molecule, has the structure of a closed ring.

The results of the new work showed that the main nucleus of the pectin molecule consists of at least 8 — 10 galacturonic acid residues and that the neuron-like components of pectin, i.e., galactose and arabinose, are only concomitant substances with respect to pectin. They are not in stoichiometric relations with the polygalacturon core and are weakly associated with the latter.

Later it was established that the pectin complex actually has a polygalacturonic core, consisting of many galacturonic acid residues, but that the latter are interconnected in an open chain. For example, using X-ray and refractometric studies of pectin nitro- and acetyl ethers, it has been proven that the pectin molecule has a chain-like structure like starch and cellulose molecules.

Along its length from the pectin molecule esters smaller than that of cellulose ethers, and greater than that of starch esters.

The carboxyl groups of galacturonic acid residues are saturated with methyl alcohol radicals.

The polygalacturonic chain of methoxylated pectin is presented according to the latest views in the following form:16.3

Each chain link is a six membered ring consisting of carbon and one to five oxygen. Separate units are connected together in positions 1: 4.

According to the available data, the molecular weight of purified pectin reaches 100 000 and above, and the polygalacturon chain contains no more than 12 galacturonic acid residues — methoxylated or devoid of methoxyls (M, respectively, equal to 190 or 176). It follows that around the 80 chains must be interconnected in one bundle to form a molecular aggregate of pectin.

Based on the fact that the polygalacturonic pectin core is resistant to the action of hydrolysing agents and possesses a positive rotation, it is assumed that the d-galacturonic acid radicals participating in the pectin core have a pyranose structure.

The quantitative content of CH30 in pectins is 10 — 12% by weight of the polygalacturonid portion. This content is CH3It corresponds to the degree of methoxylation 0 equal 75% relative to the total number of carboxyl groups polygalacturonic chains.

A number of authors discovered the presence in pectin preparations of various origin up to 13,0% acetic acid. Other authors deny the presence of acetic acid in the composition of pectin. At the moment, we can assume that acetic acid and the form of acetyl ether groups CH3CO is involved only in a part of beet pectin.

Mineral components are represented in the pectin complex in the form of Ca, M £ and their salts. In the process of the natural formation of the pectin complex, the addition of the Ca and Mg cations to the poly-galacturone chain occurs by the substitution of carboxyl hydrogen groups.

It is assumed that the ions Ca and (and other polyvalent metals), while in the pectin molecule, bind carboxyl groups of adjacent chains of principal valences and connect the latter to each other.

In addition to Ca and Mg, insignificant amounts of Fe, А1 and SiO were found in the composition of the ash of pectins.2.

The quantitative content of mineral elements in the native pectin could not be accurately determined due to the fact that the recovery of pectin from plant tissues generally occurs upon exposure to acid, which leads to a more or less strong demineralizing pectin.

It should be noted that the existing disagreements regarding the individual constituents of pectic substances are caused by the difference in methods for extracting the latter from the original material. It should also be noted that differences in the chemical composition of pectins also depend on their origin.

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