THE ELEMENTS OF PLANT FOOD 27 



of S. The most familiar forms of the proteins are 

 albumins, casein, fibrin, gluten. 



Albumins are easily coagulated by heat. The most 

 familiar albumin is that of the white of an egg. It 

 also exists in the blood and tissues of animals, and in 

 grains and vegetables. Being soluble in water, it may 

 be extracted from vegetables and meats by soaking in 

 water. Much valuable food may be lost by improper 

 cooking. Hot water will coagulate the albumin and 

 it will then remain in the article cooked, whereas cold 

 water will dissolve and extract the albumin. 



Casein represents a class of proteins found in milk. 

 A similar substance is called vegetable casein which 

 is found in plants and may be extracted from some 

 of them. Casein is not coagulated by heat, but is 

 coagulated by acids and ferments, chief of which for: 

 practical purposes is the acid and ferment obtained 

 from the inner surface of a calf's stomach, called rennet. 

 The coagulation of casein, or the making of curd, is one 

 of the necessary steps in the manufacture of cheese. 



Fibrin makes up the larger part of the fibrous portion 

 of lean meat or muscle. In its soluble form it is found 

 in the blood. 



Gluten forms one of the most important nitrogenous 

 food substances found in grains. It is present in wheat 

 and it is this which forms the sticky part of dough when 

 it is kneaded. A gum of gluten may be easily made by 

 chewing wheat for a few minutes. The saliva dis- 

 solves the starch and the gluten remains as a light- 

 colored gum. 



Note. Gluten is made up of two substances, glutenin and gliadin. 

 Gliadin is the substance that sticks together the flour particles, glutenin 

 is a grayish substance that is held together to make up the gluten. The 



