THE CARBOHYDRATES 



201 



MALTOSE. 



Maltose is found in plants and is formed in considerable quantities 

 from starch during the germination of barley and other cereals. The 

 polysaccharide is hydrolysed by the enzyme, diastase, in the grain 

 into a mixture of maltose and dextrin : 



(C 6 H 10 6 ) n + H 2 = C 12 H. 2 O n + (C 6 H 10 5 ) n _ 2 . 



Maltose is also formed by the careful hydrolysis of starch by acids, 

 and also from glycogen by the action of diastase. 



Diastase prepared from barley (30 gm.), (see p. 399), is added to 30 gm. 

 of starch or soluble starch in 3000 c.c. of water. The mixture is kept at 

 50 for 3 hours and then for 12 hours at room temperature. 60 per cent, 

 of maltose is formed. The solution is filtered, evaporated to a thin syrup 

 and poured into 95 per cent, alcohol. The precipitate of dextrin is re- 

 moved and the alcohol distilled from the solution. Maltose separates out 

 on standing. It is purified by dissolving in a little water, pouring into boiling 

 alcohol, filtering, removing the alcohol and allowing to crystallise (Baker and 

 Day, Brit. Assoc. Report, 1908, Sect. B., 671). 



. Maltose is readily soluble in water from which it crystallises in white needles 

 of the composition C 12 H 2 2On . H 2 O. 



Reactions. 



Maltose resembles glucose in its reactions more closely than lactose. 



(i ) Formation of Esters. It forms esters with eight hydroxyl groups. 



(5) Action of Alkali. Maltose gives Moore's test. 



(6) Action of Hydrochloric Acid. Maltose is hydrolysed by boil- 

 ing with dilute hydrochloric acid into two molecules of glucose. 

 Concentrated hydrochloric 



acid has the same action 

 upon it as upon glucose. 



(7) Reduction of Me- 

 tallic Hydroxides in Alka- 

 line Solution. Maltose 

 reduces Fehling's solution 

 etc., but its reducing power : 

 is less than that of glucose. 

 After hydrolysis by acids 

 the reducing power of the 

 solution is greater than 

 before hydrolysis. 



Maltose does not re- 

 duce Barfoed's reagent. 



(9) Formation of Osa- 

 zone. Maltose behaves like 



FIG. 41. Maltosazone. 

 lactose in forming an osazone with 



phenylhydrazine in acetic acid solution ; it is soluble in boiling 



