Lipids are broadly defined as any fat-soluble (lipophilic), naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The main biological functions of lipids include energy storage, acting as structural components of cell membranes, and participating as important signaling molecules. (http://en.wikipedia.org/wiki/Lipids)
The word “lipide” is defined in Webster’s Unabridged Dictionary as “any group of substances that in general are soluble in ether, chloroform, or other solvents for fats but are only sparingly soluble in water, that with proteins and carbohydrates constitute the principal structural components of living cells, and related and derived compounds, and sometimes steroids and carotenoids.” (Fennema, 1980)
Fats and oils are a combination of substances called fatty acids and glycerol. The fatty acids are long chains of carbon and hydrogen atoms, with a mildly acidic group at one end, which is where they join with glycerol to form molecules called triglycerides, which are three fatty acids joined with one glycerol.
In a simple triglyceride, the 3 fatty acids combined with the glycerides are the same. In a mixed glyceride more than one kind of fatty acid is present. The shortening ability of fat is related to this factor (Lowe, 1955)
Fats composed mainly of saturated fatty acids that are solid at room temperature and the greater the saturated fat content, the higher will be the temperature of melting. Oils on the other hand, generally stay liquid at cooler temperatures because of the greater degree of unsaturationm most oils have. These oils may also be referred to as polyunsaturated fats.examples of these fats are corn, soy, sesame, and sunflower. There are also fats called monounsaturated fats wherein they only have one double or triple bond in their chains. Examples of this kinds of fats are olive, peanut, and canola oils.
The principal uses of fats and oils in cookery are to give richness and flavor, fry or cook foods, and as shortening.
Lipids are soluble in organic solvents but not in water. Water insolubility is the analytical property used as basis for their facile separation from proteins and carbohydrates. According to Belitz, they are greasy to the touch and have lubricating properties. They are not volatile and do not leave any residue when burned.
This experiment enables one to demonstrate the effect of alkali on fats and oils, explain the chemistry behind the reaction between alkali and fats, and used to illustrate the physical properties of lipids such as solubility and specific gravity. It also enables one to relate solubility and specific gravity with chemical properties of oil samples, compare the smoke points of several fats and oils and enables one to relate the chemistry of fats and oils with their smoke points, and to compare solidification points of fats and oils. This experiment seeks to relate the chemistry of fats and oils with their solidification points, illustrate the creaming ability of various fats and enables one to relate the chemistry of fats and oils with its creaming ability and seek to demonstrate the water-absorbing capacity of commercial fats. It also seeks to relate the chemistry of fats and oils with their water absorbing capacity and to demonstrate the polymorphic behavior of fats in chocolate and how cooling rate and seeding can alter the crystal structure of chocolate in the tempering process. And this experiment was used to demonstrate how the type of fat used influences quality of margarine.