CARBOHYDRATES 49 



Type 1. Aldehyde group potentially active, reducing sugars: 



Sugar Components 



Maltose Glucose and glucose 



Gentiobiose Glucose and glucose 



Lactose Glucose and galactose 



Melibiose Glucose and galactose 



Turanose Glucose and fructose 



Type 2. Non-reducing sugars: 



Sucrose Glucose and fructose 



. Trehalose Glucose and glucose 



The disaccharides of Type 1 reduce Fehling's solution and form 

 hydrazones and osazones, although somewhat less readily than 

 do the hexoses. They all show mutarotation and exist in two 

 modifications, indicating that the component groups have the 

 closed-ring arrangement. 



The disaccharides of Type 2, since they contain no potentially 

 active aldehyde group, do not reduce Fehling's solution, nor form 

 osazones; neither do they exhibit mutarotation. The only 

 disaccharides which occur as such in plants are of this type. Di- 

 saccharides of Type 1 may be obtained by the hydrolysis of other, 

 more complex, carbohydrates. 



All disaccharides are easily hydrolyzed into mixtures of their 

 component hexoses, by boiling with dilute mineral acids, or by 

 treatment with certain specific enzymes which are adapted tp the 

 particular disaccharide in each case (see pages 55, also Chapter 

 XIV). 



Sucrose (cane sugar, beet sugar, maple sugar) is the ordinary 

 " granulated sugar " of commerce. It occurs widely distributed 

 in plants, where it serves as reserve food material. It is found in 

 largest proportions in the stalks of sugar cane, in the roots of cer- 

 tain varieties of beets, and in the spring sap of maple trees, all of 

 which serve as industrial sources for the sugar. In the sugar cane, 

 and beet-roots, it constitutes from 12 to 20 per cent of the green 

 weight of the tissue and from 75 to 90 per cent of the soluble solids 

 in the juice which can be expressed from it. Its universal use 

 as a sweetening agent is due to the combined facts that it crys- 

 tallizes readily out of concentrated solutions and, hence, can be 

 easily manufactured in solid form, and that it is sweeter than any 

 other of the common sugars except fructose. 



