fats and oils

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 Food.

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 Nutrition.

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. See also Lipid.

There are myriad culinary uses for fats and oils including cooking, tenderizing baked goods and adding richness, texture and flavor to foods. Fat is one of the body's basic nutrients, providing energy by furnishing calories. All forms of fat are made up of a combination of fatty acids, which are the building blocks of fats much as amino acids are the building blocks of proteins. Fats and oils are either saturated or unsaturated, the latter classification being broken down into monounsaturated and polyunsaturated fats. To illustrate the difference between the terms saturated, monounsaturated and polyunsaturated, picture a fat molecule as a train of passenger cars (carbon atoms). If every seat on the train is filled by a "passenger" (hydrogen atom), then this is a saturated fat molecule. If there's one seat open in each car where a hydrogen-atom "passenger" can sit, the molecule is monounsaturated; if there are several seats available, it's polyunsaturated. In general, saturated fats come from animal sources and are solid enough to hold their shape at room temperature (about 70°F). Exceptions to this rule are tropical oils such as coconut oil and palm oil, which, though of plant origin, are semisolid at room temperature and highly saturated. Saturated fats are the nutritional "bad guys" because they're known to be associated with some forms of cancer and to increase cholesterol levels, which can be a contributing factor to heart disease. In addition to the two aforementioned tropical oils, the most commonly commercially used saturated fats are butter, lard, suet and hydrogenated vegetable oils such as margarine and vegetable shortening. Hydrogenated (or partially hydrogenated) oils have been chemically transformed from their normal liquid state (at room temperature) into solids. During the hydrogenation procedure extra hydrogen atoms are pumped into unsaturated fat. This process creates trans fatty acids, converting the mixture into a saturated fat and obliterating any benefits it had as a polyunsaturate. Some researchers believe that hydrogenated oils may actually be more damaging than regular saturated fats for those limiting cholesterol in their diets. Unsaturated fats are derived primarily from plants and are liquid (in the form of an oil) at room temperature. Generally speaking, oils are composed (in varying percentages) of both monounsaturated and polyunsaturated fats. Monounsaturated fats are known to help reduce the levels of LDL (the bad) cholesterol. The three most widely used oils that are high in monounsaturates are olive oil, canola oil and peanut oil. Polyunsaturated fats are also considered relatively healthy and include the following, ranked in order, most to least, of polyunsaturates: safflower oil, soybean oil, corn oil and sesame oil. Omega-3 oils are a particular classification of fatty acids found in some plants (such as flax seed) and in the tissues of all sea creatures. These special polyunsaturated oils have been found to be particularly beneficial to coronary health (purportedly lowering the bad LDL cholesterol and elevating the good HDL) as well as to brain growth and development. Among the popular fish that are particularly good sources of Omega-3 oil (in order of importance) are sardines, herring, mackerel, bluefish, tuna, salmon, pilchard, butterfish and pompano. High cooking temperatures can destroy almost half the Omega-3 in fish, whereas microwave cooking doesn't appear to have an adverse effect on it. Canned tuna packed in water is a quick and easy way for many people to get their Omega-3 oil, but it's worth noting that combining it with the fat in mayonnaise offsets any positive effects. Canned salmon and sardines are also excellent Omega-3 sources. Storing fats and oils. Saturated fats such as butter, margarine and lard should be tightly wrapped and refrigerated. They can usually be stored this way for up to 2 weeks. Hydrogenated vegetable shortening can be stored, tightly covered, at room temperature for up to 3 months. Refined oils, sealed airtight, can be stored on the kitchen shelf up to 2 months. Oils with a high proportion of monounsaturates-such as olive oil and peanut oil-are more perishable and should be refrigerated if kept longer than a month. See also almond oil; animal fat; chili oil; cocoa butter; cottonseed oil; fat substitutes; grapeseed oil; grease; hazelnut oil; milk fat; oils; pumpkin seed oil; sunflower seed oil; trans fatty acids; walnut oil.