62 PLANT COMPOUNDS 



This constitutes another double "sugar" group. It is 

 one of the most widely distributed sugars in plants, but 

 since it is never a storage form of carbohydrates it is not 

 found in any quantity, as are the other sugars. It is one 

 of the transition forms from starch to dextrose, and is 

 formed to a large extent in the germinating seed (Section 7). 

 Of itself, however, it may serve as a transport form of 

 carbohydrate without undergoing a change to dextrose. 

 It is a white, crystalline solid, readily soluble in water; 

 slightly soluble in cold alcohol; not as sweet as sucrose. 

 It is dextrorotatory, the specific rotation being +138°. 

 Maltose reduces Fehling's solution, since it belongs to the 

 aldehyde group. Under the action of an enzyme called mal- 

 tase, it is hydrolyzed to dextrose, one molecule of maltose 

 beraking up into two molecules of dextrose. 1 It is also 

 hydrolyzed to dextrose on boiling with a dilute mineral acid 

 like hydrochloric. Maltose ferments only as it is hydro- 

 lyzed to dextrose by enzymes in the fungi and bacteria. 

 It forms compounds with alkalies and alkaline earths, but 

 they are of no importance. 



Maltose is prepared by treating starch paste with malt 

 extract (Section 7) at 60° C, and extracting the maltose thus 

 formed with successive portions of hot 87 per cent, alcohol, 

 finally evaporating and allowing it to crystallize. It is 



1 As in the case of sucrose this hydrolytic change shows the glucoside-like 

 character of maltose, it being a " gluco-glucoside, " or "glucolin." Thus: 



H 



I 

 0=C— H H— C— O— H 0=C— H 



H— O— C— H H— C— O— H H— O— C— H 



H— O— C— H = H— C— O— H + H— O— C— H 



I I I 



H— O— C— H H— C— O— H H— O— C— H 



I I I 



H— O— C— H H— C— O— H H— O— C— H 



I I I 



— H— O— C— H H— C=0 H— O— C— H 



H H 



Maltose Dextrose Dextrose 



