42 



CARBOHYDRATES 



On the other hand such disaccharides as maltose, lactose, and the 

 others in Table 3-3 do contain a potential aldehyde group and show 

 the characteristic reactions of reducing sugars, although to a smaller 

 degree than the monosaccharides. This lowered reducing power is not 

 surprising when it is remembered that even in the reducing disaccharides 

 one reducing group has been covered up in forming the disaccharide 

 linkage. The Barfoed test for monosaccharides is' based on the stronger 

 reducing power of the simple sugars as compared to the disaccharides. 



Like other glycosides, the disaccharides can be hydrolyzed, whereupon 

 they take on a molecule of water and form the corresponding simple 

 sugars. This hydrolysis may be brought about by heating the disac- 

 charide with dilute acid, or by the action of certain enzymes. Such hydro- 

 lytic enzymes are found in the digestive tracts of animals, in yeasts, bac- 

 teria, and molds, and in many higher plants. The enzymes are named 

 according to the sugar upon which they act; sucrase (also called invertase) 

 acting on sucrose, maltase on maltose and lactase on lactose. The equa- 

 tion of hydrolysis is as follows: 



CioHooOu + HoO = CeHjoOe + CeHioOe 



Sucrose Glucose Fructose 



Maltose Glucose Glucose 



Lactose Glucose Galactose 



The mixture of glucose and fructose formed by hydrolysis of sucrose is 

 called "invert sugar." Obviously it consists of equal parts of glucose 

 and fructose. 



Sucrose 



This sugar is known also as saccharose, cane sugar, beet sugar, or 

 simply "sugar." As already stated in connection with glucose and fruc- 

 tose, sucrose is generally associated with these monosaccharides in flowers, 

 fruits, roots, and seeds of plants. It is especially abundant in sugar 

 cane, sugar beet, sorghum, and the sap of the maple and palm. The 

 first two plants, which contain 16-20 per cent sucrose, are the chief 

 commercial sources of this sugar. Sorghum contains an abundance of 

 sucrose, but it has not as yet been possible to produce sugar successfully 

 from this plant. 



Annual world production of raw sugar during the last 5 years has been 

 30-35 million tons, and is still rising. About two-thirds of the total 

 is produced from sugar cane and nearly all of the rest from sugar beets. 

 The United States and its island possessions, together with the Philippine 

 Islands, produce about one-sixth of the world total. Louisiana and 

 Florida are the leading cane sugar states; California and Colorado, the 

 beet sugar states. 



The annual per capita consumption of sugar in the United States is 



