VARIOUS DISACCHARIDES 85 



MALTOSE. C^HgaOn. 



This disaccharide has not such a wide distribution in the 

 plant as has cane sugar. It occurs in the cell sap of leaves 

 and is formed, at any rate in part, by the action of diastase 

 on the starch. Maltose is produced in quantity during the 

 germination of barley and other grains by a similar enzyme 

 action. The action is hydrolytic, and may be represented 

 approximately by the following formulae : 



(C 6 H 10 6 )n + H 2 -> C 12 H M U + (C 6 H 10 O 5 ) n 

 Starch Maltose Dextrin 



The same change can also be brought about by the careful 

 hydrolysis of starch with sulphuric acid. 



Maltose is also formed by the action of diastase and other 

 enzymes on glycogen. 



In preparing maltose from starch, it is not necessary 

 always to act on the starch contained in barley, potato-starch 

 serving equally well, the diastase which is employed is usually 

 introduced in the form of malt, which is barley that has been 

 allowed to sprout and is then killed by suddenly heating to a 

 temperature sufficient to stop the further growth of the barley 

 without destroying the diastase. The malt is then stirred up 

 with starch and water, and kept at a temperature of 60-62 

 for about half an hour ; by the end of this time about 80 per 

 cent of the starch has been converted into maltose and 20 per 

 cent into dextrin. Dextrin itself is also converted into maltose 

 by diastase, but the reaction is very slow, and in practice 

 sufficient time is not allowed to effect this change. 



Properties and Reactions. 



Maltose is readily soluble in water, and crystallizes from 

 this solvent in slender white needles, having the composition 

 Ci 2 H 22 O n , H 2 O. 



1. Maltose reduces Nylander's reagent, but not Barfoed's 

 reagent. 



2. Maltose reduces Fehling's solution without previous 

 hydrolysis, and can therefore be estimated directly by this 

 means. 



3. When treated with phenylhydrazine, as described under 

 glucose, it gives an osazone (m.p. 206), which is soluble in 





