It has been difficult to provide a definition for the lass of substances called lipids. Early definitions were mainly based on whether the substance is soluble in organic solvents like ether benzene or chloroform and is not soluble in water.
In addition, definitions usually emphasize the central character of the fatty acids – that is, whether lipids are actual or potential derivatives of fatty acids.
Every definitions proposed so far has some limitations. For example, monoglycerides of the short chain fatty acids are undoubtedly lipids, but they would not fit the definition on the basis of solubility because they are more soluble in water than in organic solvents.
Up to 99 percent of the lipids in plant and animal material consist of such esters, known as fats and oils. Fats are solid at room temperature, and oils are liquid.The fat content of foods can range from very low to very high in both vegetable and animal products.
In the nonmodified foods, such as meat, milk, cereals, and fish the lipids are mixers of many of the compounds with triglycerides making up the major portions.
The fats and oil used for making fabricated foods such as margarine and shortening, are almost pure triglyceride mixtures.
Fats are sometimes divided into visible and invisible fats. About 60 percent of total fat and oil consumed consists of invisible fats – that is, those contained in dairy products (excluding butter), eggs, meat, poultry, fish, fruits, vegetables and grain products. The visible fats, including lard, butter, margarine shortening, and cooking oils, accounted for 40 percent of total fat intakes.
Lipids in general