The chemical formula of starch and other polysaccharids is written
(C₆H₁₀O₅)n. This means that the proportion of the elements is according
to the figures given, but the number of atoms that are supposed to be
combined is many times greater than five, and is not accurately known.
This is purely theoretical, and of no practical importance, except that
it shows that the polysaccharid is capable of being digested or broken
up into many simple carbohydrate compounds.
[Sidenote: Sources of starch]
Starch is the most abundant carbohydrate known. It is the chief
constituent of all cereals, and is found in large quantities in green
fruits and tuberous plants. Starch occurs in small granules, varying
greatly in size in different foods.
[Sidenote: Potato starch]
Potatoes are composed chiefly of starch and water. The starch grains of
potatoes can almost be distinguished with the naked eye. These starch
granules are not atoms or molecules in the chemical sense, but are small
receptacles in which starch has been deposited by the growing plant.
When cooked or boiled in water these starch grains swell into a mushy,
pasty or gelatinous mass; when cooked in dry heat until they begin to
turn brown, they are changed into a compound related to the gum group,
known as dextrin.
[Sidenote: Solubility of starch]
Starch does not dissolve in water as do sugars. If starch is treated
with digestive fluids, such as saliva, or with certain acids, it goes
through a complex process of digestion in which it is first turned into
soluble starch, then into the various forms of dextrin or gums, and
finally into maltose or malt-sugar.
[Sidenote: How corn-starch is changed into glucose]
Corn-starch, treated with weak sulfuric acid, changes the starch into
glucose. The ordinary glucose or corn-sirup is not all changed by this
process, into pure glucose, but contains some maltose and other gummy
compounds; hence it will not crystallize or granulate into pure sugar.
After the acid has changed the starch into glucose it (the acid) is
neutralized with an alkali. A crude compound is thus formed, which
settles to the bottom of the tank, and from which the glucose can be
easily separated. Commercial glucose is now very extensively used in
the manufacture of various food products, especially confectionery.
Pure glucose is a wholesome food, but there is some danger that the
commercial product may (due to carelessness in manufacturing, or to
the use of cheap and impure acid) contain various mineral poisons.
Government testing of glucose and similar manufactured products is, in
the writer's opinion, fully as essential as the government inspection of
packing-house products.
[Sidenote: How starch is changed into maltose]
Just as glucose may be manufactured from starch treated with dilute
acids, so maltose may be made by treating starch with malt. The brewing
of beer depends upon the chemical changes induced in starch by malt.
Barley is ordinarily used for this purpose. The barley is sprouted in
a warm, damp room, and a process of starch digestion begins, which is
necessary in order that the young barley sprouts may grow. This changes
the starch into maltose. The digestive principle developed in the
barley-malt may be utilized to malt other grains by mixing them with the
sprouted barley.
[Sidenote: Maltose in foods]
If this process of malting is stopped at the proper time, and the sugar
dissolved, and extracted, a product is formed consisting chiefly of the
sugar maltose. This is the basis of malt extract, malt honey, and many
similar foods put on the market, which are claimed by the manufacturers
to have wonderful dietetic and curative values.