Fat and oil
One of the three major classes of basic food substances, the others being protein and carbohydrate. Fats and oils are a source of energy. They also aid in making both natural and prepared foods more palatable by improving the texture and providing a more desirable flavor. See also
Fats are grouped according to source. Animal fats are rendered from the fatty tissues of hogs, cattle, sheep, and poultry. Butter is obtained from milk. Vegetable oils are pressed or extracted from various plant seeds, primarily from soybean, cottonseed, corn (germ), peanut, sunflower, safflower, olive, rapeseed, sesame, coconut, oil palm (pulp and kernel separately), and cocoa beans. Marine oils, which are not consumed in the United States, are obtained mostly from herring, sardine, and pilchard.
Fats and oils are important in the diet. They are the most concentrated form of food energy, contributing about 9 cal/g (38 joules/g), as compared to about 4 cal/g (17 joules/g) for carbohydrates and proteins. Fats make a meal more satisfying by creating a feeling of fullness, and also delay the onset of hunger. Contrary to popular belief, fats are highly digestible, with 94–98% of the ingested fat being absorbed from the intestinal tract.
The polyunsaturated fatty acids, primarily linoleic and arachidonic, are essential nutrients; that is, they are not synthesized by the body but are required for tissue development. Absence of these fatty acids from the diet results in an essential fatty acid syndrome and in a specific form of eczema in infants. Vegetable oils are an excellent source of linoleic acid, while meat fats provide arachidonic acid in small but significant amounts. Fats and oils are carriers of the oil-soluble vitamins A and D, and are the main source of vitamin E. They also have a sparing action on some of the B complex vitamins. See also
Several forms of deterioration may occur in fats and oils. Flavor and odor may develop after deodorization of a product to complete blandness. The flavor is generally characteristic of the oil source and is therefore usually acceptable. However, soybean oil can develop disagreeable flavors described as beany, grassy, painty, fishy, or like watermelon rind. Beef fat can become tallowy, which is also objectionable. Reversion is apparently caused by changes in substances which have been oxidized prior to, but not removed by, deodorization.
Oxidative rancidity is a serious flavor defect and highly objectionable. It starts with the formation of hydroperoxides which then decompose to form aldehydes which have a pungent, disagreeable flavor and odor. Retardation of oxidation is brought about by using opaque, airtight containers, or nitrogen blanketing if clear glass bottles are used. Antioxidants are required in meat fats, since lard, tallow, and so on contain no natural anti-oxidant material. Vegetable oils contain tocopherols. Additional antioxidant, with the exception of tertiary butyl hydroquinone (TBHQ), has little benefit for these oils.
Hydrolytic rancidity results from the liberation of free fatty acids by the reaction of fats and oils with water. While most fats show no detectable off flavors, coconut and other lauric acid oils develop a soapy flavor, and butter develops the strong characteristic odor of butyric acid. Packaged coconut-oil products and lauric-type hard butters sometimes contain added lecithin, which acts as a moisture scavenger, thereby retarding hydrolytic rancidity development.
Fats and oils used in deep fat frying can break down under adverse conditions, especially where frying is intermittent or the fryer capacity is not fully used. Deterioration ultimately results in the oil becoming very dark in color, viscous, foul-odored, and foaming badly during frying. The oil becomes oxidized and then polymerized, requiring that it be discarded, since it imparts strong off flavors to the fried food.
Crystal structure transformation of packaged shortening results in formation of a grainy, soft product, which may also lose incorporated gas and take on the appearance of petroleum jelly. Similar changes in crystal structure can cause bloom in chocolate coatings, a defect which gives a white haze or even open grain on an originally smooth, glossy surface. Chocolate bloom can be inhibited by the addition of lecithin or polysorbates or both.