Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

SACCHAKIFICATION OF STAKCH 401
8. SACCHARIFICATION OF STARCH AND ALCOHOLIC
FERMENTATION
Saccharification.—Potato starch 1 (100 g.) is made into a thin
sludge by stirring with water and then poured slowly into an enamelled
jar (capacity 2-5 1.) containing 1500 c.c. of boiling water,
which is kept vigorously stirred throughout with a wooden spoon.
To the thick homogeneous glassy material so obtained (after coolmg
to 40°) there is added one-third of a filtered extract, freshly prepared
by digesting 15 g. of coarsely ground kiln malt with 100 c.c. of water
at 35°-40° for one hour.
The saccharification, which should be carried out at about 40°,
is accelerated by stirring and is complete in about an hour. Its
course is followed by removing 5 c.c. of the solution a quarter of an
hour after the malt extract has been added and determining in this
sample, by the method of Willstatter and Schudel, 2 the amount of
maltose formed (see below). After thirty minutes more the determination
is repeated.
The Sugar Determination.—Dilute the 5 c.c. sample in a measuring
flask to 25 c.c. and pour 10 c.c. of this diluted solution into 25 c.c.
of 0-1 N-iodine solution. Then add 40 c.c. of 0-1 N-sodium hydroxide
solution (free from alcohol) and leave for twenty minutes. Make faintly
acid with dilute sulphuric acid and titrate back with 0-1 N-sodium
thiosulphate solution. One equivalent of iodine corresponds to 0-5
mole of reducing biose, or 1 c.c. of 0-1 N-iodine solution to 17-1 mg.
of maltose. What is the course of the reaction ?
When the consumption of iodine is the same in two successive
tests and a sample of the mixture is no longer coloured by iodine
the saccharification is complete. Usually 75-80 per cent of the
starch taken is converted into sugar. The rest of the starch is only
broken down into dextrins, which are, however, also saccharified in
the course of the subsequent fermentation. The volume of the
mash is measured in a cylinder, and from the result of the final
maltose titration the sugar content is calculated. For the CO2determination
10 c.c. are retained (cf. p. 402).
Fermentation.—The solution is next transferred to a roundbottomed
flask (capacity 3 1.) for fermentation. To set this going 10 g.
1 If it is desired to start from potatoes (500 g.), they must be heated in a digester
under 2-3 atmospheres pressure, since simple boiling till soft does not produce a
breakdown sufficient for complete saccharification.
» Ber., 1918, 51, 780.
2D