Wheat granules are of two shapes and sizes. They are embedded in a
more or less continuous matrix of gluten, a relatively larger number of
the granules being free or not embedded in the gluten of soft-wheat than
in hard-wheat flours. Larger granules average 25 to 35 microns in diame-
ter and are oval and lenticular (bun shape, being flatter on one side).
The small granules are circular and average about 3 to 5 microns. The
hilum may show as a circular spot, and striations if present are faintly
visible in large granules only.
Rice starch is composed of aggregates of granules, though the polygonal
(angular) granules are all small, 3 to 8 microns. No striations are visible
and the hilum is stellate and visible only at high magnification.
Cornstarch granules are, according to the variety, polygonal or round.
The size averages 10 to 25 microns and few aggregates are found. The
404 FLOUR AND BREAD
hilum is stellate and in the center, and sometimes shows as a crack. Stria-
tions are very indistinct.
Potato starch granules vary in size, the large ones being egg or oyster-
shaped, the small ones usually circular. The diameter is usually 60 to 100
microns but may vary from 15 to 100 microns. The hilum is an annular
or circular spot at the narrow end of the granule. The striations are usually
very distinct in large granules, somewhat ring-shaped with wider spacing
at the broad end.
Constitution o£ starch. A perusal of the literature of starch chem-
istry shows no unanimity of opinion in regard to the naming of the starch
components, their number, nor some of their properties. However, it should
be remembered that starch, as it is found in the plant tissues, is only one of
many other components. It is separated from these other components by
physical means and often, when the chemist starts to work with it, is a
modified starch, the modification occurring through physical or chemical
treatment.
Starch may occur as free starch or combined with phosphoric acid, with
phosphorus and protein, or with free fatty acids. Samec states silicic acid
is always present in starch. Many of the properties and characteristics of
starch vary with its constitution.
The starch molecule. There seems to be agreement that cellulose is com-
posed of beta-glucopyranose units, whereas starch is composed of alpha-
glucopyranose units linked into a continuous chain. The terminal units of
such a chain differ, because of their position, from one another and from
the other units in the chain. One terminal unit should have reducing
powers, just as glucose has reducing power; but the greater the number of
glucose units combined as in starch, the less the relative reducing power
should be. There is no agreement as to the number of glucose units con-
stituting starch. Haworth states that he believes the chemical unit of
starch to be composed of about 30 glucose units. However, he adds that
these chemical units must aggregate to form physical units of much larger
size. Richardson, Higginbotham, and Farrow have reported that the aver-
age chain length of starch varies from 460 to 1470 glucose units. Still
longer chains than these have been reported.
Page 327
Presented as published in 1932. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
A modernized reading is not available for this page yet. You are seeing the original text.
Wheat granules are of two shapes and sizes. They are embedded in a
more or less continuous matrix of gluten, a relatively larger number of
the granules being free or not embedded in the gluten of soft-wheat than
in hard-wheat flours. Larger granules average 25 to 35 microns in diame-
ter and are oval and lenticular (bun shape, being flatter on one side).
The small granules are circular and average about 3 to 5 microns. The
hilum may show as a circular spot, and striations if present are faintly
visible in large granules only.
Rice starch is composed of aggregates of granules, though the polygonal
(angular) granules are all small, 3 to 8 microns. No striations are visible
and the hilum is stellate and visible only at high magnification.
Cornstarch granules are, according to the variety, polygonal or round.
The size averages 10 to 25 microns and few aggregates are found. The
404 FLOUR AND BREAD
hilum is stellate and in the center, and sometimes shows as a crack. Stria-
tions are very indistinct.
Potato starch granules vary in size, the large ones being egg or oyster-
shaped, the small ones usually circular. The diameter is usually 60 to 100
microns but may vary from 15 to 100 microns. The hilum is an annular
or circular spot at the narrow end of the granule. The striations are usually
very distinct in large granules, somewhat ring-shaped with wider spacing
at the broad end.
Constitution o£ starch. A perusal of the literature of starch chem-
istry shows no unanimity of opinion in regard to the naming of the starch
components, their number, nor some of their properties. However, it should
be remembered that starch, as it is found in the plant tissues, is only one of
many other components. It is separated from these other components by
physical means and often, when the chemist starts to work with it, is a
modified starch, the modification occurring through physical or chemical
treatment.
Starch may occur as free starch or combined with phosphoric acid, with
phosphorus and protein, or with free fatty acids. Samec states silicic acid
is always present in starch. Many of the properties and characteristics of
starch vary with its constitution.
The starch molecule. There seems to be agreement that cellulose is com-
posed of beta-glucopyranose units, whereas starch is composed of alpha-
glucopyranose units linked into a continuous chain. The terminal units of
such a chain differ, because of their position, from one another and from
the other units in the chain. One terminal unit should have reducing
powers, just as glucose has reducing power; but the greater the number of
glucose units combined as in starch, the less the relative reducing power
should be. There is no agreement as to the number of glucose units con-
stituting starch. Haworth states that he believes the chemical unit of
starch to be composed of about 30 glucose units. However, he adds that
these chemical units must aggregate to form physical units of much larger
size. Richardson, Higginbotham, and Farrow have reported that the aver-
age chain length of starch varies from 460 to 1470 glucose units. Still
longer chains than these have been reported.