A textbook of domestic science for high schools

EXPERIMENT 42. — (a) Boil 1 pt. water, place two eggs in it, remove from fire, keeping kettle closely covered to retain heat. At end of six minutes, remove one egg ; remove the other at the end of ten minutes. (6) Put an egg in boiling water and let boil three and one-half minutes. Compare the consistency of the three eggs. Is there any difference ? What is the best method for cooking eggs soft ? EXPERIMENT 43. — (a) Cook an egg in boiling water for seven or eight minutes. (6) Cook an egg in water just below the boiling point for twenty minutes or longer. Compare (a) and (&). Note difference in consistency of yolks and whites. What is the best method of cooking eggs hard? What effect does the temperature of 212° F. have upon protein? Classification of Proteins. — All proteins contain nitrogen, carbon, hydrogen, oxygen, sulphur; some contain also phosphorus and iron. However, there are many forms of protein, all possessing widely varied chemical and physical properties. By such experiments as those that have been performed and others much more complicated and extended, scientists have learned enough about these substances to classify them as follows : I. Simple Proteins : A. Albumen, found in egg, blood, milk, etc. Properties : (1) Coagulates with heat (2) Soluble in water (3) Soluble in weak salt solution (4) Insoluble in strong salt solution B. Globulin, found in egg, muscle, blood, milk, etc. Properties : (1) Coagulates with heat (2) Insoluble in water (3) Soluble in weak salt solution (4) Insoluble in strong salt solution C. Alcohol-Soluble Proteins (1) Glutenin and gliadin, found in wheat, which, when mixed with water, unite to form gluten (2) Legumen of peas and beans D. Albuminoids or proteins found in skeleton and framework. Principal form is collagen, which is found in the white fibers of connective tissue and which, when boiled with water, forms gelatin Properties : (1) Dissolve in hot water (2) Form a jelly when cold E. Extractives In the animal body proteins are constantly breaking down into simpler substances, some of which contain nitrogen. At the time of killing, some of these nitrogenous substances are in the tissues; they can be extracted with water and for this reason the name " Extractives " has been given them. As a human food they serve as mild stimulants and also as flavoring materials. It is not thought, however, that they can be used as building stones. If an animal is fed on a diet in which extractives are the only nitrogenous substances, it dies of what is called nitrogen starvation. The extractives are not coagulated by heat ; they will, therefore, remain in solution when meat juice is heated. Not so, however, the albumen and globulin of meat juices; they are coagulated at a certain temperature and rise to the surface and form a scum. A beef broth, therefore, in which the proteins have been coagulated and removed by skimming or straining is wholly lacking in tissue-forming substances ; it is mildly stimulating, however, i.e. it spurs on the various processes of the body and may be the means of supplying water in a very acceptable form. II. Conjugated Proteins. — Proteins which contain some other molecule united to the protein molecule A. Phospho-proteins. — Are compounds of protein with a phos-