Foods, their selection and preparation

In making soap, fat is heated with a strong alkali, such as lye (sodium hydroxide). This splits the fatty acids off from the glycerin portion of the fat and the fatty acids combine with the sodium portion of the lye to form sodium salt or soap. The remaining portion of the fat combines with the hydroxyl por¬ tion of the lye to form glycerin. This reac¬ tion is shown in the simplified form of the equation given below: Fat + sodium hydroxide = soap -f glycerin [136] Table XXVII . Fatty Acids Frequently Found in Foods Saturated Unsaturated Butyric, 4 carbon atoms Caproic, 6 carbon atoms Caprylic, 8 carbon atoms Capric, 10 carbon atoms Laurie, 12 carbon atoms Palmitic, 16 carbon atoms Stearic, 18 carbon atoms Oleic, 18 carbon atoms, lack 2 hydrogen atoms Linoleic, 18 carbon atoms, lack 4 hydrogen atoms Linolenic, 18 carbon atoms, lack 6 hydrogen atoms KINDS OF FATTY ACIDS Most fats contain mixtures of fatty acids. At least 40 have been identified in food fats, but five of these — stearic, palmitic, butyric, oleic, and linoleic — are the ones most abun¬ dantly represented in the visible food fats. These fatty acids vary in two important respects: the number of atoms of carbon and the relative amount of hydrogen they con¬ tain. Fatty acids are called saturated when they have combined with all the hydrogen possible. In Table XXVII the more impor¬ tant fatty acids are listed as saturated or un¬ saturated. The number of carbon atoms contained and the number of hydrogen atoms lacking in the unsaturated acids are indicated. PROPERTIES OF FATS The properties of the fats and oils vary with the fatty acids they contain. All fats are insoluble in water and lighter than water. Even though salad oil is mixed thoroughly with the vinegar or lemon juice used in the preparation of French salad dressing, on standing the dressing separates into two layers, the oil on the top and the solution of acid in the water on the bottom. The fat in milk is not in solution but is held in suspen¬ sion in the form of an emulsion. On standing it separates as the cream layer on the top of the milk, because the fat is lighter than the other constituents of the milk. Instability. Fats are unstable chemically and unless carefully handled become rancid and develop disagreeable odors and flavors. This is due to decomposition resulting from a complex oxidation process and other, less understood causes. The products of decom¬ position are responsible for the unpleasant flavors and odors. Knowledge of the factors causing deterio¬ ration of fats was advanced considerably as the result of research during the war. The necessity of supplying fats and fat-containing foods to our soldiers in tropical areas and under field conditions intensified the need for such information. Although the prob¬ lems have not all been solved, it is known that deterioration of fats is hastened by high temperatures, light, and exposure to air.