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226 THE CARBOHYDRATES.
and other sugars from glucose can also Le Lrought about by means of
yeast maltase (Hill and Emmerling, see page 58). It is also formed,
besides ordinary maltose, in the action of diastase on starch paste, and
occurs in beer and in commercial starch-sugar. It is produced, with
maltose, by the action of saliva or pancreatic juice (Kulz and Vogel)
or blood-serum (Rohmann *) on starch. The formation of isomaltose
in the hydrolysis of starch has been denied by many investigators because
they considered isomaltose only as contaminated maltose.2
Isomaltose dissolves very readily in water, has a pronounced sweetish
taste, and does not ferment, or, according to some, only very slowly.
It is dextrorotatory, and has very nearly the same power of rotation as
maltose. Isomaltose is characterized by its osazone. This forms fine
yellow needles, which begin to form drops at 140° C. and melt at 150-
153° C. These are rather easily soluble in hot water and dissolve in hot
absolute alcohol much more readily than the maltosazone. Isomaltose
reduces copper as well as bismuth solutions.
Lactose (milk-sugar). As this sugar occurs exclusively in the animal
world, in the milk of human beings and animals, it will be treated in a
following chapter (on milk).
3. Colloid Polysaccharides.
If we exclude the not well known trisaccharides and the tetrasaccharide
stachyose this group includes a great number of very complex carbo-
hydrates which occur only in the amorphous condition, or at least not
as crystals in the ordinary sense. Unlike the bodies belonging to the
other groups, these have no sweet taste. Some are soluble in water,
while others swell up therein, especially in warm water, and finally
some are neither dissolved nor visibly changed. Polysaccharides are
ultimately converted into monosaccharides by hydrolytic cleavage.
The polysaccharides are ordinarily divided into the following groups:
starches with the dextrins, plant gums and mucilages, and the celluloses.
Starch Group.
Starch, amylum (CeHic-C^x. This substance occurs in the plant
kingdom very extensively distributed in the different parts of the plant,
especially as reserve food in the seed, roots, tubers, and trunks.
Starch is a white, odorless, and tasteless powder, consisting of small
1
Kulz and Vogel, Zeitschr. f. Biologie, 31; Rohmann, Centralbl. f. d. med. Wis-
eh., 1893, 849.
2
Brown and Morris, Journ. of Chera. Soc, 1895; Chem. News, 72. See also Ost
Ulrich, and Jalowetz, Ref. in Ber. d. deutsch. chem. Gesellsch., 28; Ling and Baker,
Journ. of Chem. Soc, 1895; Pottevin, Chem. Centralbl., 1899, II, 1023.
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