CARBOHYDRATES. 39 



The disaccharides have the general formula C^H^Ou, to which, 

 in the process of hydrolysis, a molecule of water is added causing 

 the single disaccharide molecule to split into two monosaccharide 

 (hexose) molecules. The products of the hydrolysis of the more 

 common disaccharides are as follows : 



Maltose = dextrose + dextrose. v 

 Lactose = dextrose -f- galactose. 

 Sucrose = dextrose + laevulose. 



All of the more common disaccharides except sucrose have 

 the power of reducing certain metallic oxides in alkaline solution, 

 notably those of copper and bismuth. This reducing power is due 

 to the presence of the aldehyde group ( CHO) in the sugar 

 molecule. 



MALTOSE, C 12 H 22 11 . 



Maltose or malt sugar is formed in the hydrolysis of starch 

 through the action of an enzyme, vegetable amylase (diastase), con- 

 tained in sprouting barley or malt. Certain enzymes in the saliva 

 and in the pancreatic juice may also cause a similar hydrolysis. 

 Maltose is also an intermediate product of the action of dilute mineral 

 acids upon starch. It is strongly dextro-rotatory, reduces metallic 

 oxides in alkaline solution and is fermentable by yeast after being 

 inverted (see Polysaccharides, page 43) by the enzyme maltase 

 of the yeast. In common with the other disaccharides, maltose may 

 be hydrolyzed with the formation of two molecules of monosac- 

 charide. In this instance the products are two molecules of dex- 

 trose. With phenylhydrazine maltose forms an osazone, maltosa- 

 zone. The following formula represents the probable structure of 

 maltose : 





