l64 ORGANIC AGRICULTURAL CHEMISTRY 



Monosaccharoses the Final Product of the Digestion of 

 Carbohydrates. — The digestive action upon carbohydrates 

 consists in their conversion into the final form of one of the 

 three monosaccharoses, viz, glucose, frudose or galactose, C6H12O6. 

 These simple sugars, therefore, are the only carbohydrate foods 

 which do not require digestion, but are directly absorbed as they 

 are. All other forms of carbohydrate food, whether soluble or 

 insoluble, must be digested ; and this digestion consists in their 

 conversion into one or more of the three named monosaccharoses. 

 The chemical reactions involved in the conversion of the disac- 

 charoses and polysaccharoses into monosaccharoses have been 

 considered in the first section of our study. In the laboratory 

 this conversion may be brought about by hydrolysis with dilute 

 acids or alkalies. In the animal body it is always accomplished 

 by the action of hydrolytic enzymes. In the chapters on carbo- 

 hydrates and on enzymes these reactions have all been con- 

 sidered, but it is well to review them here before we take up the 

 digestive action in the animal body. 



Hydrolysis of Disaccharoses and Polysaccharoses. — All of 

 the disaccharoses commonly occurring in food, viz. cane sugar, 

 milk sugar and malt sugar, are hydrolyzed by particular enzymes 

 into monosaccharoses as follows : 



C12H22O11 + H2O by sucrase (invertase) -> C6H12O6 + C6H12O6 



Cane sugar Glucose Fructose 



or sucrose 



C12H22O11 -h H2O by lactase -> C6H12O6 + CeHigOs 



Milk sugar Glucose Galactose 



or lactose 



C12H22O11 + H2O by maltase — > 2 C6H12O6 



Malt sugar 2 Glucose 



or maltose 



The polysaccharoses, starch and dextrin, are hydrolyzed by 

 enzymes into maltose. Cellulose yields galactose and mannose. 



2 (CeHioOB):^ + H2O by ptyalin or diastase — >■ x C12H22O11 



Starch, or dextrin (animals) (plants) ' Maltose 



