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STARCH. 227
granules which have ;i stratified structure and different shape and size
in different plants. Starch is considered insoluble in cold water. The
grains swell up in warm water and hurst, yielding a paste.
According to the ordinary opinion the starch granules consist of two
different substances, starch granulose and starch cellulose (v.
Nageli), the first of which turns blue with iodine and forms the chief
part of the granule. According to Maquenne and Roux 1
this is
not the fact. According to them the starch granule consists of two
constituents, of which the .first, amylase, forms the chief mass (80-85
per cent) and the other, amijlopectin, forms only 15-20 per cent of the
granule. Amylopectin is not identical with v. Nageli’s starch cellulose,
and the above investigators consider starch cellulose as only an insoluble
form of amylase. The amylose can occur in two forms; one, which is
soluble, is colored blue by iodine and is immediately transformed into
sugar by malt, the other is a solid substance, which is not colored
with iodine and resists the action of malt infusion. One modification
can be transformed into the other.
In the paste, besides amylopectin, we also have soluble amylose, and
this can, by a process called retrogradation by Maquenne and Roux, be
transformed into the solid modification, " artificial starch." This
solid form occurs in the starch granule, and is identical with v. Nageli’s
starch cellulose. As the starch granules are directly colored blue by
iodine they must, besides this, also contain soluble amylose. If the author
understands the above investigators correctly the starch granules con-
tain three constituents, namely, soluble amylose, which is colored blue
by iodine ( = starch granulose), insoluble amylose, which is not colored
by iodine ( = starch cellulose), and amylopectin.
In the formation of paste the amount of amylose is not the essential
but rather the quantity of amylopectin. The amylopectin is a slime-
like substance, insoluble in boiling water and dilute alkalies, only becom-
ing pasty therein, and not colored blue by iodine. Accordingly the
paste is a solution cf amylose made thick by amylopectin. The amylo-
pectin, unlike the amylose, is only slowly transformed into sugar with
dextrin formation. Starch is insoluble in alcohol and ether. On heat-
ing starch with water alone, or heating with glycerin to 190° C, or on
treating the starch grains with 6 parts dilute hydrochloric acid of sp. gr.
1.06 at ordinary temperature for six to eight weeks,2
it is converted into
soluble starch (amylodextrin, amidulin). Soluble starch is also
*v. Nageli, Botan. Mitteil., 1863; Maquenne and Roux, Compt. rend., 138, 140,
142, 146, and Bull. Soc. chim. de Paris (3), 33 and 35.
2
See Tollens’ Handb., 191. In regard to other methods, see Wr6blewsky, Ber. d.
deutsch. chem., Gesellsch., 30; Syniewski, ibid.
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