characteristic appearance of starch granules may be shown
by placing a very thin slice of potato under a low-power
microscope. These granules vary in size even from the
same plant, but they may be recognized by peculiar mark-
ings upon the surface as well as by shape. The starch
seems to be deposited in layers around one or more nuclei,
— hence concentric rings may be observed. When subjected
to water and low heat, these layers absorb the water, and
thus the markings disappear. If the boiling temperature
be used, the starch granule loses its regular form, becoming
a paste which is slightly sweet and very gummy. Cold
water does not form a solution with starch.
When starch is heated with dilute acids, it forms a clear
solution. W^ater seems to have united with it. The last
product of this reaction is grape sugar. A ferment in the
saliva changes starch into a sugar. A similar change takes
place in the starch of seeds on germination. This may be
shown by chewing in succession barley and the germinated
barley known as malt. The first will be tasteless, whereas
the germinated barley is sweet with sugar.
Dextrin. — Dry starch may be heated. and thus changed
into a product which is yellowish in color and soluble in
water ; this is called dextrin. It is the basis of British
gum and of library paste. Long-continued heat causes the
dextrin to become brown and bitter. This product is called
caramel.
Beyond this stage the product is soon transformed
into carbon. Water is driven out, thus leaving carbon
free.
Iodine Reaction. — Starch paste gives a blue color with
iodine solution, so that its presence even in minute
quantities may be detected. This is used in connection
with the microscope to detect adulteration of spices with
foreign starches. The test may be easily applied to so-
66 HANDBOOK OF DOMESTIC SCIENCE
called baby foods, where starch, should not be present, as
the very young baby cannot digest starchy foods.
The simplest way to determine the amount of starch in a
food is to reduce it to powder in a mortar, and mix with
water to form a medium dough. Tie the dough in a loosely
woven cloth, so that no part except starch may escape.
Place the bag of dough in a bowl of cool water and knead
with the fingers till no more starch can be washed from it.
This is shown when the water runs clear, not milky, from
the bag. Let the starchy water stand till all starch has
settled, drain or siphon off the water. Dry the starch in
the sun and weigh. If the weight of food is known, the
ratio will show roughly the amount of starch in the food.
The residue in the bag will be cellulose and insoluble
proteins. If it be flour which is examined, the product is
largely gluten, and may be examined at this time.
Digestion of Starch. — Daring the mastication of food any
starches are mingled with the saliva, which, if. its re-
action is alkaline, begins the transformation of starch into
a sugar. The partially transformed starch on reaching the
stomach meets an acid secretion which in the course of half
an hour usually neutralizes the alkaline saliva. The
stomach ferments have no action upon starch, hence it
passes without further change into the small intestine.
Here the change into soluble sugars is completed by other
ferments secreted by the pancreas and by the intestine.
Page 36
Presented as published in 1900. 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
characteristic appearance of starch granules may be shown by placing a very thin slice of potato under a low-power microscope. These granules vary in size even from the same plant, but they may be recognized by peculiar markings upon the surface as well as by shape. The starch seems to be deposited in layers around one or more nuclei, — hence concentric rings may be observed. When subjected to water and low heat, these layers absorb the water, and thus the markings disappear. If the boiling temperature be used, the starch granule loses its regular form, becoming a paste which is slightly sweet and very gummy. Cold water does not form a solution with starch.
When starch is heated with dilute acids, it forms a clear solution. W^ater seems to have united with it. The last product of this reaction is grape sugar. A ferment in the saliva changes starch into a sugar. A similar change takes place in the starch of seeds on germination. This may be shown by chewing in succession barley and the germinated barley known as malt. The first will be tasteless, whereas the germinated barley is sweet with sugar.
Dextrin. — Dry starch may be heated. and thus changed into a product which is yellowish in color and soluble in water ; this is called dextrin. It is the basis of British gum and of library paste. Long-continued heat causes the dextrin to become brown and bitter. This product is called caramel.
Beyond this stage the product is soon transformed into carbon. Water is driven out, thus leaving carbon free.
Iodine Reaction. — Starch paste gives a blue color with iodine solution, so that its presence even in minute quantities may be detected. This is used in connection with the microscope to detect adulteration of spices with foreign starches. The test may be easily applied to so-
called baby foods, where starch, should not be present, as the very young baby cannot digest starchy foods.
The simplest way to determine the amount of starch in a food is to reduce it to powder in a mortar, and mix with water to form a medium dough. Tie the dough in a loosely woven cloth, so that no part except starch may escape. Place the bag of dough in a bowl of cool water and knead with the fingers till no more starch can be washed from it. This is shown when the water runs clear, not milky, from the bag. Let the starchy water stand till all starch has settled, drain or siphon off the water. Dry the starch in the sun and weigh. If the weight of food is known, the ratio will show roughly the amount of starch in the food. The residue in the bag will be cellulose and insoluble proteins. If it be flour which is examined, the product is largely gluten, and may be examined at this time.
Digestion of Starch. — Daring the mastication of food any starches are mingled with the saliva, which, if. its reaction is alkaline, begins the transformation of starch into a sugar. The partially transformed starch on reaching the stomach meets an acid secretion which in the course of half an hour usually neutralizes the alkaline saliva. The stomach ferments have no action upon starch, hence it passes without further change into the small intestine. Here the change into soluble sugars is completed by other ferments secreted by the pancreas and by the intestine.