DIASTASE 479 



of extract is the end point, the diastatic power is 50 ; if the 

 tube containing 0-3 c.c. of extract is the end point, the diastatic 

 power is 33-3 and so on, for the more enzyme required to hydro- 

 lyse the unit of starch in unit time, the lesser is the diastatic 

 activity. Since no two samples of malt will exactly contain 

 the same amount of moisture, the amount of moisture in the 

 sample must be found from the dry weight and allowed for 

 in the calculation ; moreover malt prepared from oats has 

 only about 30 per cent of the diastatic power of barley malt, 

 while maize malt is still weaker. The diastatic power of 

 brewers' malt is about 20-40° on the Lintner scale. 



A convenient method for comparing the diastatic activity 

 of two malt extracts consists in determining the relative 

 times taken by the two extracts in hydrolysing a given starch 

 solution up to the point at which it gives no colour with a 

 dilute iodine solution ; this is the so-called achromic point 

 method. For this purpose, into a number of serially labelled 

 test tubes are pipetted 5 c.c. of a i per cent solution of soluble 

 starch and the series are placed in a water bath at 40° C. To 

 these tubes are serially added i, 3, 5 . . . c.c. of a stock 

 solution of diastase heated to 40° C, the time of addition being 

 noted. At frequent intervals a drop of the mixture is placed 

 on a white glazed tile together with a drop of dilute iodine 

 solution. When a colour is no longer produced, the time is 

 noted. That tube in which the reaction is completed in rather 

 less than three minutes should be chosen for an accurate 

 redetermination. The conventional diastatic value, D, is 

 given by the formula — 



D = , V^^. x5 



no. of CCS. of diastase t 



in which n is the number of cubic centimetres of starch solution 

 employed, and t the time taken to effect decoloration. 



From this D becomes the number of cubic centimetres of 

 starch solution which can be hydrolysed by i c.c. of diastase. 



TAKADIASTASE. 

 In addition to malt diastase, another variety, known as 

 takadiastase, is commonly used in biochemical work ; it is a 

 product of Aspergillus oryzcs and is prepared from the mycelium 



