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DEXTRINS. 229
Glycogen. This carbohydrate, which stands to a certain extent
between starch and dextrin, is principally found in the animal kingdom,
hence it will be considered in a subsequent chapter (on the liver).
Dextrins and Gums.
The dextrins stand in close relation to the starches, and are formed
therefrom as intermediate products by the action of acids or diastatic
enzymes. They yield as final products only hexoses, indeed only glu-
cose, on complete hydrolysis. The vegetable gums, the vegetable
mucilages and the pectin bodies, which all stand close to the hemicellu-
loses, yield, on the contrary, abundance of pentose and, among the hex-
oses. galactose is very often found.
Dextrin (starch-gum, British gum), is produced on heating starch to
200-210° C., or by heating starch, which has previously been moistened
with water containing a little nitric acid, to 100-110° C. Dextrins are
also produced by the action of dilute acids and diastatic enzymes on
starch. There have been numerous investigations as to the steps
involved in the last-mentioned process, but they have led to conflicting
views. One of these, which used to be generally accepted, is as follows:
The first product, which gives a blue color with iodine, is soluble starch
or amylodextrin, which on further hydrolytic cleavage yields sugar and
erythrodextrin, which is colored red by iodine. On further cleavage of
this erythrodextrin more sugar and a dextrin, achroodextrin, which is
not colored by iodine, is formed. From this achroodextrin after suc-
cessive splittings Ave have sugar and dextrins of lower molecular weights
formed, until finally we have sugar and a dextrin, maltodextrin, which
refuses to split further, as final products. The views are rather contra-
dictory in regard to the number of dextrins which occur as intermediate
steps. The sugar formed is maltose (or in first place isomaltose), and
only very little glucose is produced. Another view is that first several
dextrins are formed consecutively in the successive splittings, by hydra-
tion, and then finally the sugar is formed by the splitting of the last
dextrin. According to Moreau, in the first stages of saccharification
amylodextrin, erythrodextrin, achroodextrin and sugar are formed sim-
ultaneously. Other investigators, especially Syniewski, have recently
suggested other views on the subject. 1
This question has taken another direction by the investigations c£
1
In regard to the various views on the theories of the saccharification of starch,
see Musculus and Gruber, Zeitschr. f. physiol. Chem., 2; Lintner and Dull, Ber. d. d.
chem. Gesellsch., 26 and 28; Brown and Heron, Journ. of Chem. Soc, 1S79; Brown
and Morris, ibid., 1885 and 1S89; Moreau, Biochem. Centralbl., 3, 648; Syniewski,
Annal. d. Chem. u. Pliarm., 309, and Chem. Centralbl., 1902, 2.
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