Stearic acid
Stearic acid (ˈstɪərɪk , stiˈærɪk ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a soft waxy solid with the formula . The triglyceride derived from three molecules of stearic acid is called stearin. Stearic acid is a prevalent FA in nature, found in many animal and vegetable fats, but is usually higher in animal fat than vegetable fat. It has a melting point of 69.4 °C and a pKa of 4.50. Its name comes from the Greek word στέαρ "stéar", which means tallow. The salts and esters of stearic acid are called stearates. As its ester, stearic acid is one of the most common saturated fatty acids found in nature and in the food supply, following palmitic acid. Dietary sources of stearic acid include meat, poultry, fish, eggs, dairy products, and foods prepared with fats; beef tallow, lard, butterfat, cocoa butter, and shea butter are rich fat sources of stearic acid. Of the saturated fatty acids consumed in the United States, stearic acid consumption is second (26% of total saturated fatty acid intake) to palmitic acid (56% of total saturated fatty acid intake). Stearic acid is more abundant in animal fat (up to 33% in beef liver) than in vegetable fat (typically less than 5%). The important exceptions are the foods cocoa butter (34%) and shea butter, where the stearic acid content (as a triglyceride) is 28–45%. Examples of the use of stearic acid in food manufacturing include baked goods, frozen dairy products, gelatins, puddings, hard candy, and nonalcoholic beverages. In biosynthesis, stearic acid is produced from carbohydrates via the fatty acid synthesis machinery wherein acetyl-CoA contributes two-carbon building blocks. Stearic acid is obtained from fats and oils by the saponification of the triglycerides using hot water (about 100 °C). The resulting mixture is then distilled. Commercial stearic acid is often a mixture of stearic and palmitic acids, although purified stearic acid is available. Commercially, oleic acid, as found in palm and soy, can be hydrogenated to give stearic acid.
