Page 7 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL VIII

•

• DIASTASE 3

• • hydrogen sulphide. The precipitate is filtered off, washed, the filtrate
I evaporated to remove hydrogen sulphide and the residue made up to
the original volume
Diastase (Amylase), -This enzyme is technically of greatest
importance and is the one most often examined in analytical practice.
• Pancreatin, malt diastase and taka diastase are official pharma-
ceutical preparations, Malt extracts are largely used by bakers and
in the textile industry for which purpose a high diastatic power is
• required. The importance of diastatic power determinations in the
case of malt has already been dealt with (Vol. 1, page 136).
The methods in use are of two kinds: () the saccharification
methods in which the maltose produced by the enzyme acting on
an excess of soluble starch is measured; (2) the liquefaction methods
in which the power of the enzyme to form products which no longer
give a colouration with iodine solution, is determined.
I
t
Lintner Value. s usual to estimate the amount of enzyme neces-
i
• sary to produce a given change, the temperature, time and concen-
tration of the substrate being fixed. The simplest and most rapid
process is to ascertain when starch is absent by the iodine test, but
it is more accurate to estimate the maltose formed.
This process is carried out as described in Vol. 1, p. 137. A series
of test-tubes each receives roc.c. of a 2% solution of soluble starch and
progressively increasing quantities of enzyme solution-o.1, o,2 c.c.,
etc. After an hour 5 c.c. of Fehling's solutto (Vol. 1, p. 318) are added
to each tube and after mixing they are heated in the water bath for
o minutes. On examination one of the tubes will prove to be colour-
less, those on either side of it being faintly blue or yellow. o.1 c.c. of
enzyme is taken as having a diastatic power of too, when the maltose
it produces is equivalent to 5 c.c. of Fehling's solution. If c.c. of
enzyme were required in the experiment the diastatic power;9.1199
¢
The procedure adopted by the malt analysis committee of the
Institute of Brewing is given in Vol. 1, p. 136.
Sherman, Kendall and Clark (J. Amer. Chem. Soc., 1910, 32,
1o73) have submitted the older methods to careful criticism; when
testing commercial preparations of pancreatic diastase they find that
most of them give unsatisfactory results. Apparently these pancreatic
preparations are too poor in electrolytes to function normally when
caused to act upon pure starch dissolved in pure water. Accordingly
sodium chloride and disodium phosphate are always added so as to
The recent work of these authors on amylase, J, Awer, Ce, Sod, 1910, 332, 1087; 1911,
33, 1195is of very great importance in this field.