1 86 AGRICULTURAL CHEMISTRY 



cold water upon starch ? (2) How did this difference show itself 

 in the tests? (3) Why in the one test-tube were there a blue mass 

 and a clear liquid, and in the other opposite results ? 



240. Dextrin is a carbohydrate which has the same 

 general formula as starch from which it differs in struc- 

 tural composition. Dextrin is produced from starch by 

 the action of heat. At a temperature of 163 C. moist 

 starch is changed to dextrin. When this change takes 

 place, nothing is added to or taken from the starch mole- 

 cule. The three elements, C, H and O, are simply rear- 

 ranged in a different way in the new molecule. Dextrin 

 is not found naturally in food products to any apprecia- 

 ble extent, but is present in starch-containing foods which 

 have been subjected to the action of heat. The brown 

 crust of bread is composed mainly of dextrin. Dextrin 

 is soluble in water, and is more readily digested than 

 starch, but has the same general fuel and energy- produ- 

 cing value. 



Experiment 4.7. Preparation of dextrin. Place about 2 grams 

 of flour in a porcelain dish ; heat cautiously on a sand-bath for five 

 minutes constantly stirring, so that it will not burn. When cool, 

 add three times its bulk of water and heat nearly to boiling ; ob- 

 serve the appearance of the solution ; then filter. The filtrate con- 

 tains dextrin. To a portion, add twice its bulk of alcohol; the 

 dextrin is precipitated. To another portion, add a few drops of 

 iodin solution ; blue color indicates soluble but unaltered starch. 



Questions, (i) What agent was employed to change the starch 

 to dextrin? (2) How does dextrin differ from starch in solubility? 

 (3) Is dextrin soluble in alcohol ? (4) In what ways does dextrin 

 differ from starch ? 



241. Structural Formulas. Cellulose, starch, dextrin 

 and inulin have the same general formula (C 6 H 10 O 5 ) n , but 



