124 ORGANIC AGRICULTURAL CHEMISTRY 



mixture and continue to boil a few minutes. This is a colloidal sus- 

 pension of starch and is known as starch paste. 



(4) Test this starch paste solution with iodine solution. Dilute 

 the starch paste 10, 100 and 1000 times, and test each with iodine 

 solution. 



(5) Dilute 5 c.c. starch paste, with 100 c.c. water, add 5 c.c. of con- 

 centrated HCl and boil for 10 to 15 minutes. Neutralize excess acid 

 with Na2C03 and test a little with iodine solution, and another por- 

 tion with Fehling's solution. The starch is hydrolyzed by boiling 

 with acids as follows : 



(C6Hio05)x+ X H2O -> ic CeHisOe 



Starch Glucose 



Dextrin 



When starch is hydrolyzed by diastase or ptyalin, and also 

 probably by acids, dextrin is formed as an intermediate prod- 

 uct between starch and maltose. Dextrin is soluble in cold 

 water, forming a sirup with adhesive properties, and is used 

 commercially in several ways. It is optically active, being dextro- 

 rotatory, and reduces Fehling^s solution. It is non-fermentable 

 with zymase. Toward iodine, dextrin acts in different ways 

 indicating the existence of several varieties. One form, know^n 

 as erythro-dextrin, is colored reddish brown with iodine. An- 

 other form known as achr 00 -dextrin is colorless with iodine. 

 Achroo-dextrin is also known in three varieties called a-, ^8- and 

 y-achroo-dextrin. All of these varieties of dextrin have been 

 proven as intermediate between starch and maltose in the 

 enzymatic hydrolysis of starch. 



Glycogen 



Glycogen is known as animal starch. It resembles starch 

 and is found in the animal body. It is present in the liver and 

 in the muscle cells as a reserve form of carbohydrate food 

 material. It is broken down in the body, yielding glucose. 

 This will be considered further in connection with animal 

 metabolism. 



