Nomenclature of the pectic substances. The dififerent names used
in the literature for pectin and its related compounds have been numerous.
To avoid confusion, the Committee on the Nomenclature of the Pectic
Substances (Dore, Chairman) have proposed dividing these into three
groups: (1) protopectin, (2) pectin, and (3) pectic acid. The chemical
identity of the various pectic substances is not definitely settled, but a
great deal of investigational work is being done at the present time.
Function of pectic substances in plant life. The pectic substances
play an important role in plant life. Dore states that the primary function
of the pectic substances is the cementing together of the individual cells
that compose the plant.
Sources of pectin in plants. The pectic substances are found in the
leaves, bark, roots, tubers, stalks, and fruits of plants. The pectic com-
pounds occur in two places in the plant cell — in the middle lamella, where
154 JELLY
they serve as cementing material, and as thickened places on the cell wall.
These two sources may yield slightly different substances. In fruits the
pectin is usually found in the pulp and not in the juice, though there are
some exceptions. For example, currant juice often contains pectin. The
skins and cores of fruit like apples contain large proportions of pectin.
Hence, apples and crab-apples are cut into small pieces, but not peeled
or cored, for making jelly. Some of the root stocks, such as sugar beets,
carrots, rutabagas, and turnips, contain appreciable amounts of pectin.
The amount of pectin not only varies in different fruits, but also in the
same fruit at various stages of ripeness and in the same fruit in different
years or seasons.
Protopectin. Protopectin has been called pectose and pectinogen. It
is the water-insoluble pectic substance in plants. It may be rendered soluble
by the enzyme protopectinase or by treatment with acid and other reagents.
The soluble substances thus formed are designated as pectins.
Sucharipa has presented evidence that the protopectin is combined with
cellulose. In the plant, the separation of the pectin from the cellulose is
brought about by hydrolysis by the enzyme protopectinase.
The protopectin is the precursor of pectin. As the fruit ripens, pectin
increases while the protopectin decreases. Protopectin is also converted to
pectin by boiling with dilute acid. Since fruit juices contain acid, some
protopectin is changed to pectin when the fruit is boiled. This is the reason
why cooked fruit juices are better for jelly than uncooked ones.
Conrad', influenced by Ehrlich's work, found that as the pectin of the
fruit increases, a pentose-bearing polysaccharide is liberated at the same
time from the protopectin, its proportions paralleling that of the pectin
to a great extent. This furfural-yielding polysaccharide is separated from
the pectic substances by its solubility in 70 per cent alcohol.
Pectin. Among the various names that have been applied to pectin are
parapectin, pectinogen, and protopectin. The term is applied to the meth-
ylated pectic substances that form a colloidal solution in water. It is the
jelly-forming substances of the pectic compounds, although the pectins with
fewer methyl groups have less jellying power than those with a greater
number.
Page 124
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Nomenclature of the pectic substances. The dififerent names used
in the literature for pectin and its related compounds have been numerous.
To avoid confusion, the Committee on the Nomenclature of the Pectic
Substances (Dore, Chairman) have proposed dividing these into three
groups: (1) protopectin, (2) pectin, and (3) pectic acid. The chemical
identity of the various pectic substances is not definitely settled, but a
great deal of investigational work is being done at the present time.
Function of pectic substances in plant life. The pectic substances
play an important role in plant life. Dore states that the primary function
of the pectic substances is the cementing together of the individual cells
that compose the plant.
Sources of pectin in plants. The pectic substances are found in the
leaves, bark, roots, tubers, stalks, and fruits of plants. The pectic com-
pounds occur in two places in the plant cell — in the middle lamella, where
154 JELLY
they serve as cementing material, and as thickened places on the cell wall.
These two sources may yield slightly different substances. In fruits the
pectin is usually found in the pulp and not in the juice, though there are
some exceptions. For example, currant juice often contains pectin. The
skins and cores of fruit like apples contain large proportions of pectin.
Hence, apples and crab-apples are cut into small pieces, but not peeled
or cored, for making jelly. Some of the root stocks, such as sugar beets,
carrots, rutabagas, and turnips, contain appreciable amounts of pectin.
The amount of pectin not only varies in different fruits, but also in the
same fruit at various stages of ripeness and in the same fruit in different
years or seasons.
Protopectin. Protopectin has been called pectose and pectinogen. It
is the water-insoluble pectic substance in plants. It may be rendered soluble
by the enzyme protopectinase or by treatment with acid and other reagents.
The soluble substances thus formed are designated as pectins.
Sucharipa has presented evidence that the protopectin is combined with
cellulose. In the plant, the separation of the pectin from the cellulose is
brought about by hydrolysis by the enzyme protopectinase.
The protopectin is the precursor of pectin. As the fruit ripens, pectin
increases while the protopectin decreases. Protopectin is also converted to
pectin by boiling with dilute acid. Since fruit juices contain acid, some
protopectin is changed to pectin when the fruit is boiled. This is the reason
why cooked fruit juices are better for jelly than uncooked ones.
Conrad', influenced by Ehrlich's work, found that as the pectin of the
fruit increases, a pentose-bearing polysaccharide is liberated at the same
time from the protopectin, its proportions paralleling that of the pectin
to a great extent. This furfural-yielding polysaccharide is separated from
the pectic substances by its solubility in 70 per cent alcohol.
Pectin. Among the various names that have been applied to pectin are
parapectin, pectinogen, and protopectin. The term is applied to the meth-
ylated pectic substances that form a colloidal solution in water. It is the
jelly-forming substances of the pectic compounds, although the pectins with
fewer methyl groups have less jellying power than those with a greater
number.