CARBOHYDRATES 



45 



The figure 95 per cent is obtained from the hydrolysis equation of 

 sucrose and is the ratio of tlie niolccuhnr weight of sucrose to the sum 

 of the molecular weights of glucose and fructose, the sugars of which 

 invert sugar is composed (342 -^ 360 = 0.95). 



Optical Rotation of Sucrose. The rotation of polarized light is the 

 basis for determining sucrose by means of a saccharimcter. This instru- 

 ment enables the beet sugar manufacturer to determine what he should 

 pay for his beets and the custom house official to decide what should be 

 the import duty on a cargo of sugar. It is as important to tlie sugar 

 industry as the "Babcock Tester" is to the dairy industry and serves 

 as an outstanding example of an abstract physical property becoming 

 of great economic value. 



Sucrose is dextrorotatory (+66.5), but invert sugar is levorotatory 

 ( — 19.85) because fructose rotates polarized light more to the left 

 (—92.4) than glucose does to the right (+52.7). Because the rotation 

 is reversed (inverted) when sucrose is hydrolyzed, the hydrolysis of 

 sucrose is called "inversion." The change in the direction of rotation 

 is also the reason for the terms "invert sugar" and "invertase" — the 

 name of the enzyme that effects the hydrolysis. Sucrase is a better name 

 for this enzyme because it denotes which sugar is hydrolyzed. The term 

 "inversion" can be properly applied only to the hydrolysis of sucrose 

 because the hydrolysis of other sugars is not accompanied by a change 

 in the direction of optical rotation. By determining the rotation of a 

 sugar solution, for example, from cane, beets, fruits, and so on, before 

 and after hydrolysis, the percentage of sucrose may be determined because 

 the change in rotation is directly proportional to the quantity of sucrose 

 present. The saccharimcter enables the analyst to determine in a few 

 minutes the percentage of sucrose and thus puts all operations in the 

 sugar industry on an exact basis. 



Malt 



ose 



This disaccharide is widely distributed in leaves and young seedlings 

 and is especially abundant in germinating seeds. It is the principal 

 sugar formed by the action of the digestive enzymes ptyalin and amylopsin 

 on starch and glycogen. In the germination of seeds a starch-splitting 

 enzyme, diastase, is produced and brings about the conversion of the 

 insoluble starch into a soluble sugar, maltose, which is utilizable by the 

 plant cells. Additional information on starch-splitting enzymes is given 

 on p. 58. 



Malt sirups can be made from the water-soluble material of germinated 

 barley. Also a sirup can be prepared from the sweet potato' by steeping 

 the finely cut potato in water at 40°C. for a few hours. After being 

 filtered from insoluble material, the solution is concentrated to a thick 

 sirup, having the flavor of the sweet potato. 



