Page 9 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL VIII

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DIASTASE 5
• I This is known as the achromic point; the time taken to reach it must
I be between and ro minutes, failing which, the quantity of enzyme
solution must be suitably altered.
Five cubic centimetres of enzyme solution and 5 c.c. of starch solu-
tion are warmed separately to 40° and mixed at a given time; the
• mixture is tested with iodine every minute until the achromic point
is reached. The method is very rapid though less accurate than
the others described.
• Modifications of this method have been described by Francis (Bl-
letin Pharmacy, 1898, 12, 52), Takamine (J. Soc. Chem. Ind., 1898, 17,
118, 437) and Johnson (J. Amer. Chem. Soc., 1908, 30, 798).
Sherman, Kendall and Clark (J. Amer. Chem. Soc., 1919, 32, 1073)
use a 1% solution of potato starch which they have boiled for 2 hours.
25oc.c. of this are digested with the enzyme at 4o° until o.25 c.c. when
removed and mixed with 5 c.c. of dilute iodine' solution in a test-tube
• shows no colour differing from that of the untreated iodine solution.
The amount of enzyme is found which completes the digestion in 30
minutes { ± r min.) and the result expressed by dividing the weight
of starch (a.5 grm.) by the weight of enzyme required to digest it. This
method gives parallel results to the Lintner method.
Wohlgemuth (Biochem. Zeitsch., 1908, 9, 1) proposes to make use
of the iodine colouration by working in the following manner:
Increasing quantities of the enzyme solution are filled into a series
of test-tubes and the whole placed in ice while s c.c. of 1% starch
solution are added to each. 'The tubes are kept 3o or 6o minutes
at 4o° and replaced in ice water. They are then nearly filled with
water, a drop of N/o iodine solution added to each and the contents
shaken. Colours varying from dark blue, bluish-violet, reddish-
yellow to yellow are obtained. The tube in which the violet colour,
just shows is taken as indicating complete hydrolysis to dextrin and
the amount of enzyme in it recorded. If this, for example, contained
o.o2 c.c. saliva the diastatic power is expressed as D 40°/30=- 250,
i.e., 1c.c. saliva at 4o° in 3o minutes hydrolyses soc.c. of 1% starch
solution.
It has been suggested to use starch paste in Metts' tubes for dias-
tatic power determinations but this method does not give satisfactory
results,
In the case of malt extracts suitable for the textile industries it is
the liquefying power which is of importance, comparisons based on
the Lintner standard being valueless. The analysis of such malt
_
'grm. iodine and 4 grm. potassium iodide in so c.c. water. For use a cc. are
diluted to roo and s cc. taken for each test.