Acid. When starch pastes are treated with acid, hydrolysis of the gluco-
side linkages takes place and shortening of the molecular chain occurs.
Richardson, Higginbotham, and Farrow suggest that the attack occurs at
random along the starch chains, so that in any paste of acid-modified starch
there is a wide distribution of chains of varying length. As hydrolysis pro-
ceeds an increasing number of shorter chains is produced, the reducing
power is increased, and the stiffening power decreased. Hydrolysis with
acid is more rapid as the temperature increases, which gives an explanation
for adding lemon juice to the partially cooled gel of water, cornstarch,
sugar, and egg yolk. Hydrolysis is also speeded by increasing the concen-
tration of the acid.
Boiling and enzyme hydrolysis. Hydrolysis is also brought about by
diastatic enzymes and by boiling with water, the last more rapidly under
pressure at temperatures above boiling.
Commercial soluble starch. The commercial soluble starches should not
be confused with soluble starch occurring naturally in food products.
Commercial soluble starches have been treated, usually with acid, and
although they are more soluble, their properties, such as stiffening power,
are also modified.
The effect of acid upon the thickening power of starch has been known
for a long time. If cornstarch, lemon juice, and water are boiled together,
the resulting paste is not as thick as one made with the same amount of
cornstarch and liquid, but without the acid.
Sugar and starch. Woodruff and Nicoli have reported that pastes made
from 5 grams of corn, wheat, rice, potato, arrowroot, or cassava starch
and 95 grams of water required heating to 90°C. or higher before the
cooled gels were strong enough to retain the shape of a mold. When
10, 30, 50 or 60 grams of sucrose were added to the above quantities the
three root starches formed increasingly softer gels with increasing amount
of sugar, the 50 and 60 grams giving a sirup. Although the three cereal
starches showed increasing transparency and tenderness with increase of
sugar, a gel that would not mold was not obtained until more than 50
grams of sucrose were added. A sirup was obtained with 60 grams of sugar
and the cereal starches.
The Results of Fine or Over-Grinding upon Flour
Bakers have known for a long time that flour ground too finely does
not produce so good a quality of bread as flour that has not been over-
ground. Alsberg and Griffing have reported the following for over-ground
flour. Before over-grinding, the starch granules clumped together under
the microscope; in the over-ground flour they were scattered. Over-grind-
ing injured the starch, and as previously stated the greater the degree of
injury the more the starch was dispersed. Diastase acted on the whole
granule rather slowly, but with many injured granules and the increase in
412
FLOUR AND BREAD
Page 334
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Acid. When starch pastes are treated with acid, hydrolysis of the gluco-
side linkages takes place and shortening of the molecular chain occurs.
Richardson, Higginbotham, and Farrow suggest that the attack occurs at
random along the starch chains, so that in any paste of acid-modified starch
there is a wide distribution of chains of varying length. As hydrolysis pro-
ceeds an increasing number of shorter chains is produced, the reducing
power is increased, and the stiffening power decreased. Hydrolysis with
acid is more rapid as the temperature increases, which gives an explanation
for adding lemon juice to the partially cooled gel of water, cornstarch,
sugar, and egg yolk. Hydrolysis is also speeded by increasing the concen-
tration of the acid.
Boiling and enzyme hydrolysis. Hydrolysis is also brought about by
diastatic enzymes and by boiling with water, the last more rapidly under
pressure at temperatures above boiling.
Commercial soluble starch. The commercial soluble starches should not
be confused with soluble starch occurring naturally in food products.
Commercial soluble starches have been treated, usually with acid, and
although they are more soluble, their properties, such as stiffening power,
are also modified.
The effect of acid upon the thickening power of starch has been known
for a long time. If cornstarch, lemon juice, and water are boiled together,
the resulting paste is not as thick as one made with the same amount of
cornstarch and liquid, but without the acid.
Sugar and starch. Woodruff and Nicoli have reported that pastes made
from 5 grams of corn, wheat, rice, potato, arrowroot, or cassava starch
and 95 grams of water required heating to 90°C. or higher before the
cooled gels were strong enough to retain the shape of a mold. When
10, 30, 50 or 60 grams of sucrose were added to the above quantities the
three root starches formed increasingly softer gels with increasing amount
of sugar, the 50 and 60 grams giving a sirup. Although the three cereal
starches showed increasing transparency and tenderness with increase of
sugar, a gel that would not mold was not obtained until more than 50
grams of sucrose were added. A sirup was obtained with 60 grams of sugar
and the cereal starches.
The Results of Fine or Over-Grinding upon Flour
Bakers have known for a long time that flour ground too finely does
not produce so good a quality of bread as flour that has not been over-
ground. Alsberg and Griffing have reported the following for over-ground
flour. Before over-grinding, the starch granules clumped together under
the microscope; in the over-ground flour they were scattered. Over-grind-
ing injured the starch, and as previously stated the greater the degree of
injury the more the starch was dispersed. Diastase acted on the whole
granule rather slowly, but with many injured granules and the increase in
412
FLOUR AND BREAD