Gliadin. Gliadin, either as a multiple protein, or as a component of
the gluten complex, is soluble in 60 to 70 per cent alcohol. In water it swells
to a sticky mass, being least soluble at its isoelectric point about pH 6.5.
With increasing acidity it becomes more soluble, reaching a maximum with
a pH range of 2.0 to 3.0. With hydrogen-ion concentration greater than
pH 2 the solubility decreases gradually. With increasing alkalinity, the
solubility of gliadin increases more rapidly than on the acid side, up to pH.
13.1, the most alkaline of the solutions used by Tague.
Glutenin. It is the glutenin, classified as a glutelin, that gives the
desirable baking qualities to wheat flour, qualities not possessed by any
other cereal. Glutenin is insoluble in water, but is increasingly soluble in
dilute acids and alkalies. Sharp and Gortner state that the maximum
solubility occurs on the acid side at /»H 3.0 and on the alkaline side at />H
11. The isoelectric range, as determined by Sharp and Gortner, is from
pH 6.0 to 8.0, and by Bungenberg de Jong as pH 5.6. Glutenin swells
in water. If prepared with sodium salicylate it is said to resemble gluten
in its coherence and tenacity.
Gluten
The characteristics of gluten gain in importance because it is the protein
of the flour as a whole, regardless of whether it is composed of one, few, or
many components, that gives the baking quality to flour. When water is
416 FLOUR AND BREAD
added to flour, the proteins gradually absorb about 200 per cent of their
weight in water.
When flour is made into a stiff dough and kneaded for a short time,
the starch can be washed out, leaving a small part of the original dough
which is known as gluten. Gluten is rubbery, tenacious, and elastic. It
is usually a light gray or slightly yellowish color. A large part of the gluten
is composed of the proteins gliadin and glutenin. In addition to the protein,
the gluten as washed from the dough contains some starch which is
entangled in the gluten, some lipoids, mineral salts, and water. The amount
of all these constituents of gluten varies with the manipulation in wash-
ing, the kind of water used, and the character of the flour itself. The
physico-chemical properties of gluten have been extensively studied and
applications made to baking bread.
Since gliadin and glutenin have about the same isoelectric point, rang-
ing around />H 6.5 to 7.0, Bailey states, *'it might be anticipated that
maximum coherence and extensibility of gluten and dough should be
encountered in about the same range."
Heat coagulation of gluten. Gluten seems to have no definite coagu-
lation temperature. Alsberg and Griffing have reported that heating the
gluten decreases its power to swell in acid solutions, the swelling power
decreasing during heating from 50° to 80°C. Except at the temperatures
60° to 65°C. no information was obtained that indicated a definite coagu-
lation temperature. They state that denaturation takes place over the
whole range from 50° to 80°C. The swelling power was not impaired
but probably increased at temperatures from 30° to 50 °C.
Page 338
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Gliadin. Gliadin, either as a multiple protein, or as a component of
the gluten complex, is soluble in 60 to 70 per cent alcohol. In water it swells
to a sticky mass, being least soluble at its isoelectric point about pH 6.5.
With increasing acidity it becomes more soluble, reaching a maximum with
a pH range of 2.0 to 3.0. With hydrogen-ion concentration greater than
pH 2 the solubility decreases gradually. With increasing alkalinity, the
solubility of gliadin increases more rapidly than on the acid side, up to pH.
13.1, the most alkaline of the solutions used by Tague.
Glutenin. It is the glutenin, classified as a glutelin, that gives the
desirable baking qualities to wheat flour, qualities not possessed by any
other cereal. Glutenin is insoluble in water, but is increasingly soluble in
dilute acids and alkalies. Sharp and Gortner state that the maximum
solubility occurs on the acid side at /»H 3.0 and on the alkaline side at />H
11. The isoelectric range, as determined by Sharp and Gortner, is from
pH 6.0 to 8.0, and by Bungenberg de Jong as pH 5.6. Glutenin swells
in water. If prepared with sodium salicylate it is said to resemble gluten
in its coherence and tenacity.
Gluten
The characteristics of gluten gain in importance because it is the protein
of the flour as a whole, regardless of whether it is composed of one, few, or
many components, that gives the baking quality to flour. When water is
416 FLOUR AND BREAD
added to flour, the proteins gradually absorb about 200 per cent of their
weight in water.
When flour is made into a stiff dough and kneaded for a short time,
the starch can be washed out, leaving a small part of the original dough
which is known as gluten. Gluten is rubbery, tenacious, and elastic. It
is usually a light gray or slightly yellowish color. A large part of the gluten
is composed of the proteins gliadin and glutenin. In addition to the protein,
the gluten as washed from the dough contains some starch which is
entangled in the gluten, some lipoids, mineral salts, and water. The amount
of all these constituents of gluten varies with the manipulation in wash-
ing, the kind of water used, and the character of the flour itself. The
physico-chemical properties of gluten have been extensively studied and
applications made to baking bread.
Since gliadin and glutenin have about the same isoelectric point, rang-
ing around />H 6.5 to 7.0, Bailey states, *'it might be anticipated that
maximum coherence and extensibility of gluten and dough should be
encountered in about the same range."
Heat coagulation of gluten. Gluten seems to have no definite coagu-
lation temperature. Alsberg and Griffing have reported that heating the
gluten decreases its power to swell in acid solutions, the swelling power
decreasing during heating from 50° to 80°C. Except at the temperatures
60° to 65°C. no information was obtained that indicated a definite coagu-
lation temperature. They state that denaturation takes place over the
whole range from 50° to 80°C. The swelling power was not impaired
but probably increased at temperatures from 30° to 50 °C.