DIGESTION 271 



have been identified by their reactions and have been given ap- 

 propriate names. 



(1) Amylodextrin is nearest starch. It makes up a large per- 

 centage of "soluble starch" and is even slightly soluble in cold 

 water. It turns blue with iodine. (2) Erythrodextrin is easily 

 soluble in cold water and with iodine gives a reddish-brown color. 

 (3) Achroodextrin gives no reaction with iodine and has a faintly 

 sweetish taste. Commercial dextrin is a mixture of all of these 

 and gets its sweet taste from this last-named constituent. 



The dextrins are then acted upon by dextrinase to form maltose, 

 which has been discussed with the carbohydrates (Chap. XII). 

 Maltose is then broken down by means of maltase to form 

 glucose. 



Diastase is the mixture of carbohydrate enzymes which trans- 

 forms the starch found in leaves, seeds, and places of especial 

 digestive activity such as tubers and other storage organs, into 

 sugar. That found in leaves is called diastase of translocation, 

 while that in seeds is spoken of as diastase of secretion correspond- 

 ing to the two starches of the same names, although it should be 

 added that Pringsheim (1926) concluded there was no especial 

 " translocation " starch differing from the normal. While these 

 two enzymes produce the same results, the former has an optimum 

 temperature of about 48° C. and the latter an optimum of about 

 55° C. Both act best in neutral solutions. Commercial diastase is 

 obtained from germinated barley seeds, while the brand known 

 as taka diastase comes from the action of the fungus, Aspergillus, 

 on rice or wheat. Since diastase converts starch to hexose sugars, 

 it is really a mixture of amylase, amylopectinase, dextrinase, and 

 maltase. 



Invertase (sometimes called sucrase or saccharase) is very com- 

 monly distributed in plants. It acts in a neutral or slightly acid 

 medium and breaks down (hydrolyzes) cane sugar into dextrose 

 and levulose. Although cane sugar is soluble, it seems necessary 

 in most cases that it be broken down still further before the mol- 

 ecules can penetrate the protoplasm of the cells. In beetroots 

 where much cane sugar is stored and used, no invertase has been 

 found, which has led some observers to conclude that here the 

 cane sugar must travel as such. The peculiar structure of the 

 beetroot may permit the transport of the larger molecules; but 

 this necessity in general for the further hydrolysis of cane sugar 



