CHEMICAL COMPOSITION OF PLANTS 57 



Diastase can be easily obtained from germinating grain, or 

 malt. The finely ground dry malt is soaked in water, the result- 

 ing decoction is filtered, and the filtrate then precipitated with 

 alcohol. The white, flaky precipitate is filtered off and again 

 dissolved in water. When added to a starch paste, this solution 

 will hydrolyze it rapidly. After a short time, the blue iodine 

 coloring characteristic of starch begins to change, first to 

 \'iolet, then to red, then to a yellowish color; and finally, the 

 solution ceases to give the iodine reaction. With Fehling's 

 solution, it will, however, show a distinct test for sugar. A 

 detailed chemical analysis will show that instead of starch, 

 maltose is present. 



The action of diastase, accordingly, differs somewhat from the 

 behavior of inorganic catalysts, such as strong acids, which 

 attack the molecule, or, more exactly, the colloidal aggregate of 

 starch, and rapidly break it up into the end product of hydrolysis, 

 glucose. Whereas diastase acts more slowly, as is indicated 

 by the gradual disappearance of the color reaction with iodine, 

 the whole process usually stops at the maltose stage. Diastase 

 reduces step by step the colloidal aggregate that is called starch; 

 in other words, it increases the degree of its dispersion. It 

 produces first the intermediate products of the breaking-up 

 process, the dextrines, and then maltose, when its action ceases. 

 It is not able to split maltose into glucose. 



Besides its gradual action, diastase differs from inorganic 

 catalysts also in its specificity. It can act only upon starch 

 and produces no effect on the reserve celluloses, which are 

 hydrolyzed by acids with no greater difficulty than is starch. 

 Likewise, it has no effect on either inulin or cane sugar. 



Only a very small amount of cUastase is present in dormant 

 seeds. During the early stages of germination, therefore, the 

 decomposition of starch proceeds very slowly. At the time of 

 swelling, however, the quantity of diastase in the seed increases 

 noticeably, and during the first few days of germination it shows 

 a marked increase. At the end of the first week of germination, 

 the amount of diastase is usually three to four times as great 

 as it was at the completion of swelling. 



This increase of diastase during the progress of germination 

 takes place only in the presence of a sufficient supply of oxygen 

 and is most closely connected with the very active respiration 



