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H2C-OH H2C-OCR

Fatty acid Glycerol Triglyceride

Triglycerides may range from solid to liquid consistency at room temperature depending on the fatty acid esters they contain. Solid triglycerides are commonly called fats, and liquid triglycerides, oils. If all three fatty acids that comprise the triglyceride are the same, it is called a single triglyceride; conversely, if the fatty acids differ, the triglyceride is mixed.

Triglycerides typically comprise about 95% of fat or oil. The other components include free fatty acids, mono-glycerides, diglycerides, phosphatides, sterols, vitamins, natural antioxidants, color-causing pigments, minerals, flavor-odor compounds, and other substances. Free fatty acids are the uncombined or unesterified fatty acids present in a fat or oil. Crude oils may contain several percent fatty acids, which result from hydrolysis. The formation of free fatty acids via hydrolysis leaves the partial glycerides (mono- and diglycerides) behind. Monoglycerides and diglycerides are frequently used in foods as emulsifiers. They are often found in functional cake and icing shortenings. They are produced commercially by the alcoholysis reaction of triglycerides or fatty acids with glycerol or by es-terification of glycerol with fatty acids (1).

Phosphatides are found in fat and oil from plant and animal sources. These materials consist of a polyhydric alcohol (usually glycerol) that is esterified with fatty acids, phosphoric acid, and a nitrogen-containing compound. The most common phosphatide is a family of compounds found in soybean oil referred to as lecithin, which includes chemical lecithin (phosphatidyl choline), cephalin (phosphatidyl ethanolamine), lipositols (phosphatidyl inositol) (2). Sphingomyelins are a group of phosphatides that contain no glycerol (3). Lecithin is typically used as a food additive for its emulsification properties. Phosphatides are essentially removed in the refining process.

Colored materials occur naturally in fats and oils and generally are a result of two classes of pigments. Carote-noids and chlorophylls are the yellow-red and green colors, respectively, found in fats. Level and type of pigment vary greatly with the source, from the orange color of crude palm oil due to its carotene content to the dark green color of canola (or rapeseed) oil due to its high chlorophyll content. Vegetable oils also contain tocopherols that serve as natural antioxidants, retarding oxidation, and as a source of the essential nutrient vitamin E. Other antioxidants may be added to processed fats to preserve freshness (4,5). In contrast, meat fats contain negligible levels of tocopherols.

Sterols are common minor components of all natural fats and oils. Cholesterol, the infamous sterol associated with heart disease, is the principal sterol found in animal fats. Vegetable oils only contain trace quantities of cholesterol. Vegetable oils contain other sterols that vary in type and quantity with the vegetable oil source (6—13).

Fats and oils may contain a number of other minor constituents such as waxes, gums, hydrocarbons, and fatty alcohols. These materials are generally of little importance and are typically handled during processing.

Fatty Acids

The key to understanding the chemical and physical characteristics of a fat is understanding the component fatty acids that comprise the triglyceride. These can vary in chain length (number of carbon atoms), type of carboncarbon bonding (saturated or unsaturated with hydrogen), and stereochemistry both within the fatty acid and its position in the triglyceride. The most common edible fatty acids are aliphatic, straight chain, saturated and unsaturated, containing an even number of carbon atoms and ending in a carboxyl group.

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