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 not so far been isolated, since, using currently known methods of separation of pectin, we always get a partially hydrolyzed protopectin along with its products of hydrolysis.
Like cellulose, protopectin is insoluble in cold water, but unlike cellulose is easily hydrolyzed with hot water and is not soluble in Schweitzer's reagent (solvent for cellulose). He does not have the ability to studneobrazovaniyu, which is peculiar to only some products of its shallow hydrolysis.
The hydrolysis of protopectin in water begins with the temperature 80 — 85 °. At the same time, protopectin is split into soluble pectin substance (this substance is pectin itself) and cellulose.
When processing protopectin weak solutions of acids and alkalis occurs acidic or alkaline hydrolysis protopectin. As a result of such hydrolysis is obtained as a mixture of dissolved pectin, which structure does not coincide with the pectin composition obtained by hydrolysis with hot water.
On the composition and structure of protopectin currently still no consensus. Chemical and microscopic studies of several authors led to the assumption that protopectin is a compound of pectin and cellulose, as an intermediate form between these substances.
Studies botanists using x-ray and color reactions found that protopectin plant tissue, particularly the sort of it which is found in the intercellular spaces, is composed predominantly of insoluble calcium polygalacturonate or calcium and magnesium salts of pectin and pectic acids (pectinates and pectates Ca and Mg).
The stiffness of unripe fruits due to the presence in them protopectin. Natural protopectin hydrolysis takes place in a living plant tissue mainly by enzymes. This process is similar to that described above thermal hydrolysis. It is assumed that this enzyme acts protopektinaza.
There are indications that the natural transformation protopectin develop under the action of hydrogen peroxide produced in the fruit tissue. Education is aterekisi catalysis dehydrogenases present in the plant tissue. This hypothesis has not received full confirmation.
Equally important for the occurrence of natural hydrolysis protopectin has an action of sunlight (thermal and chemical) and the action of acids contained in the composition of the fruit. The more fruits exposed to the sun's rays and the higher acidity of the fruit, the more intense the natural hydrolysis protopectin passes, as well as the further disintegration of pectin.
Hydrolysis protopectin most studied in the fruit. This process is taking place in the fresh fruit, it causes the external changes that characterize the ripening of fruits.
As protopectin passes into soluble pectin, the pulp cells, which were previously firmly bonded together, are surrounded by a milder gelatinous mass of soluble pectin. The fruits gradually become softer, due to the disconnection of the cells of the tissue, the loosening of the pulp, characteristic for the ripening of the fruit, occurs. This process is the opposite of the process of fruit growth. During growth, green fruits, as well as other green parts of the plant, perform known creative functions (the phenomenon of photosynthesis, etc.). The process of maturation is basically the process of destruction of the fetus, in which the phenomena of decomposition of the original substance (splitting of carbohydrates, acids, etc.) predominate. Hydrolysis of pectin substances is one of the most striking manifestations of this decay.
The above relates mainly to the fruits or plant parts that are exposed to sunlight (the fruit trees and shrubs, sunflower baskets). Pectin root crops (beets, carrots, etc.) Are not exposed to acids and direct sunlight, so their hydrolysis in plant tissue develops much more slowly and as a part of their predominant protopektinovaya insoluble fraction.