Fats and Oils
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Fats and Oils
Description / Application / Shipment and Storage
The fats and oils of commerce
There are four primary sources of the fats and oils of commerce. They are animals, oil-bearing trees, oil-seed crops and fish.
Tallow and grease
These products, mainly from beef cattle but also from sheep and goats, and lard from pigs, are animal body fats. Only the top quality tallow, that classified by the New York Produce Exchange as Edible, is used for food. It is produced by using either low temperatures, say 60°C, in open pans, or higher temperatures in enclosed systems but, in any case, only best quality raw material will yield best quality tallow. The upper portion of the molten fat, the premier jus (or ‘first juice’) yields a quality dripping. Poorer quality tallows, those containing increasing proportions of free Fatty Acids, are used for industrial purposes.
Pig fat is recovered in a similar way; highest quality for lard, the remainder for industrial purposes. The properties of lard make it a desirable ingredient in many recipes and it is freely available.
Butter is a milk product and its production, storage and handling are different in almost every respect from those of edible oils. Consumption of butter has been falling in developed countries in favour of margarine which, as some people seem to forget, is also essentially an agricultural product. The raw materials of margarine include animal fats as well as vegetable oils, but, like butter, margarine is itself a finished food product and, as indicated above, both are handled differently from edible oils.
Oil-bearing tree products
The classic oil-bearing tree is the olive tree (Olea Europa). The importance of olive oil in the Mediterranean is well known and it is used almost exclusively in cooking and as a salad oil. It is prepared by crushing and pressing the fruit within a day or two of harvest lest increasing free fatty acids lower the quality. The best quality oil, ‘virgin oil’ is obtained from the first pressing of the fruit and is simply clarified. Later pressings may require neutralizing, washing, bleaching and deodorizing. Some olive oil is used in the manufacture of cosmetics, pharmaceuticals and soap.
Coconut oil is a product of the coconut palm (Cocos nucifera), a tree of as much importance min the tropics round the world as the olive is in the Mediterranean. In Asian and Pacific countries this tree contributes building materials, matting, ropes and food and although the Philippines currently produces about half the world output of coconut oil, the production of copra, the dried meat of the coconut, is the mainstay of some of the small Pacific island countries. Drying reduces the weight handled and slows spoilage during storage and transport. Copra is dried in the sun, in an oven, or over fires of coconut shells. The oil is recovered by pressing and more of this is now done in the country of origin. Coconut oil is solid at ambient temperatu7res in temperate climates. It is a very saturated oil but has a high proportion of lauric (C12) and myristic (C14) acids. It is used a lot in the manufacture of soap and detergents but also in cooking fats and margarine.
The oil palm (Elaeis guineenis) is now one of the world’s most important sources of oil. The centre of palm oil production has shifted from West Africa where it originated, to Southeast Asia, where a sophisticated oil processing industry developed in Malaysia. But the palm flourishes in humid conditions in a band of 20° nof latituted straddling the equator and is now also cultivated in Central and South America.
Palm oil production now exceeds that of tallow, butter and all seed oils except soya bean oil and this has been due very largely to the development of plantations in Malaysia following the decline of rubber planting and the establishment by the government of the Palm Oil Research Institute of Malaysia (PORIM) which dates from 1979. Like olive oil, palm oil is a fruit coat fat. Fruitlets grow in bunches of up to 20 kg and each fruitlet contains a kernel surrounded by an oil pulp. This pulp yields palm oil and the kernel yields palm kernel oil, an oil of different characteristics. Because the pulp contains a lipase which splits the triglycerides, Palm Oil tends to contain relatively more free Fatty Acids than good quality crude seed oils. They are removed during refining but in order to minimize damage and losses the bunches are steamed to inactivate the lipase as quickly as possible after harvesting. Palm oil has two other special characteristics, one negative and one positive. It is orange-red because of a high content of carotene and this must be removed during refining; but it also contains an unusually high concentration of natural antioxidants which protect it in considerable measure from oxidative rancidity. The oil is recovered by boiling the fruit, centrifuging or pressing; neutralizing, bleaching and deodorizing follow. After drying the nuts, palm kernel oil is recovered by pressing or, mainly, by solvent extraction and is similarly treated to yield a refined oil. Palm kernel oil contains 40-52% of lauric acid and 14-18% of myristic acid, and thus resembles coconut oil. Palm oil is 32-47% palmitic acid and 40-52% oleic acid. It is thus more unsaturated than palm kernel oil but more saturated than the seed oils. Palm oil is shipped in many different forms: palm oil, crude, semi-refined, refined; palm olein; palm stearin; palm kernel oil; palm kernel olein; palm kernel stearin. There are therefore stricter handling procedures for these products than with, say, crude degummed soya bean oil which is to be further processed in any case. PORIM has been active and quite successful in developing food uses for palm oil which has become an important cooking and frying oil and is the basis of vanaspati (‘vegetable ghee’) in India, Pakistan and other countries of the region. It is used in margarine and in substitutes for Cocoa Butter and coating fats.
Other palm kernel oils
A number of different Central and South American tropical palm trees yield palm kernel oils similar in characteristics to coconut oil and the kernel oil of the oil palm. These include babassu, tucum, murumuru, and cohune oils which have a commercial value and are usable for the same purposes as palm kernel and coconut oils. They are considered by the National Institute of Oilseed Products (NIOP) and FOSFA to be acceptable cargoes immediately prior to the shipment of the major edible oils.
A number of fats are obtained from tropical trees. Of these the most important is cocoa butter, a product of the cocoa tree (Theobroma cacao). It is a key constituent of chocolate and an important commodity in its own right, but cocoa butter is produced largely from Cocoa Beans in countries to which the beans are consigned and, with other vegetable butters, falls outside the scope of this article.
Oil seed crop products
Soya bean oil
Soya bean (Soja max) is a legume now grown widely round the world, especially in Asia and the Americas. It is easily the world’s biggest oil seed crop, the major producers being the USA, Brazil, China and Argentina with the USA producing nearly one third as much again as the other three combined. Thousands of varieties of the plant have been tested, and production of Soya Beans and, from them, of soya bean oil, has reached a high degree of efficiency. Soya beans are stored from harvest to the tome if processing. At 18% moisture in sub-tropical temperatures mould growth is rapid; at 13-15% moisture satisfactory storage is achievable only at cooler ambient temperatures, but if the beans are to be held for a year or more, 12% is desirable. This means that some drying is often done in the fields, frequently with hot gases from mobile oil burners. From storage, the beans are cleaned, cracked, dehulled and flaked before extraction with an oil solvent, which is usually ‘commercial hexane’. This solvent is a mixture of hydrocarbons with a boiling point of 66-69°C. Heptane and cyclo-hexane are also used. The extraction yields defatted flakes and a solution which is filtered and from which the solvent is recovered for further use leaving the Crude Oil as the main product. The crude oil is mixed with about 1% of water which hydrates the gums (or lecithin) and these are removed by centrifuging to yield soya bean lecithin and crude degummed soya bean oil as the main product. This last is the usual commodity shipped to refineries which produce refined, bleached, deodorized (RBD) oil, although RBD oil itself is sometimes shipped. Because hydrocarbons have been detected in shipments of oil and have become the subject of claims and counter-claims, it should be noted from the above that there are three possible sources of hydrocarbons in soya bean oil before it arrives at the ship.
- Hydrocarbons naturally occurring in the soya bean
- Hydrocarbons from drying gases
- Residual solvent
Soya bean oil consists of about two thirds of polyunsaturated oils. The relatively high proportion of linolenic acid with its concomitant oxidative and flavour instability has led to genetic manipulation to reduce the linolenic acid content but this acid happens to be one of the n-3 acids, which, in fish oils, are currently thought to confer health benefits.
Soya bean oil is now the major food oil. It is the base for salad oils, for cooking oils, for the manufacture by hydrogenation of shortenings of specified properties, and for the manufacture of margarine.
Oil seed brassicas (B. campestris and B. napus) are grown increasingly in Europe and Canada. Rapeseed was introduced into Canada in 1940 to offset a shortage of oil and for many farmers is now a welcome alternative to wheat. Rapeseed oil contains up to 50% of the long chain fatty acid C22:1, erucic acid, and this oil is used in North America for a number of lubricating purposes. Rapeseed oil is produced by crushing and solvent extraction for the uses to which other edible oils are put, but the removal of residual solvent from the meal is more difficult than for most other seeds. Rapeseed oil is largely a monosaturated oil but current thinking suggests that these oils also are physiologically beneficial.
These are the body oils of, mainly, small fish taken in the North Atlantic and North and South Pacific oceans. In the North Atlantic, the Scandinavian countries take capelin, herring, sandeel and Norway pout, and the Americans menhaden. The Japanese sources of fish oil are mackerel and sardines, the South African, pilchards; Peru, Chile and Ecuador harvest the anchovy. The whole fish are cooked, pressed and the oil separated from the pressings by centrifugal separators. The solid residue yields fish meal and the aqueous phase fish solubles, which are either spray dried or condensed. But these are by-products, the primary product is the oil. Fish oil differ chemically from vegetable oils in being even more polyunsaturated and in the variety of fatty acids present, some with four, five and even six double bonds. Because of the high degree of unsaturation, fish oils are vulnerable to oxidation but respond to hydrogenation and, although there are industrial applications, even the burning of them as fuel oil, most of the fish oils are used in the production of hardened fish oils for the manufacture of shortenings and margarine. Lightly hardened fish oils yield salad oils.
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Although the words "oils", "fats", and "lipids" are all used to refer to fats, "oils" is usually used to refer to fats that are liquids at normal room temperature, while "fats" is usually used to refer to fats that are solids at normal room temperature. "Lipids" is used to refer to both liquid and solid fats, along with other related substances, usually in a medical or biochemical context. The word "oil" is also used for any substance that does not mix with water and has a greasy feel, such as petroleum (or Crude Oil), heating oil, and Essential Oils, regardless of its chemical structure.
Fats form a category of lipid, distinguished from other lipids by their chemical structure and physical properties. This category of molecules is important for many forms of life, serving both structural and metabolic functions. They are an important part of the diet of most heterotrophs (including humans). Fats or lipids are broken down in the body by enzymes called lipases produced in the pancreas.
Examples of edible animal fats are lard, fish oil, butter/ghee and whale blubber. They are obtained from fats in the milk and meat, as well as from under the skin, of an animal. Examples of edible plant fats include peanut, soya bean, sunflower, sesame, coconut and olive oils, and Cocoa Butter. Vegetable shortening, used mainly for baking, and margarine, used in baking and as a spread, can be derived from the above oils by hydrogenation.
These examples of fats can be categorized into saturated fats and unsaturated fats. Unsaturated fats can be further divided into cis fats, which are the most common in nature, and trans fats, which are rare in nature but present in partially hydrogenated vegetable oils.
Saturated and unsaturated fats
A fat's constituent fatty acids may differ in the C/H ratio. When all three fatty acids have the formula CnH(2n+1)CO2H, the resulting fat is called "saturated". Values of n usually range from 13 to 17. Each carbon atom in the chain is saturated with hydrogen, meaning they are bonded to as many hydrogens as possible. Unsaturated fats are derived from fatty acids with the formula CnH(2n-1)CO2H. These fatty acids contain double bonds within carbon chain. This results in an "unsaturated" fatty acid. More specifically, it would be a monounsaturated fatty acid. Polyunsaturated fatty acids would be fatty acids with more than one double bond; they have the formula, CnH(2n-3)CO2H and CnH(2n-5)CO2H. Unsaturated fats can be converted to saturated ones by the process of hydrogenation. This technology underpinned the development of margarine.
Saturated and unsaturated fats differ in their energy content and melting point. Since unsaturated fats contain fewer carbon-hydrogen bonds than saturated fats with the same number of carbon atoms, unsaturated fats will yield slightly less energy during metabolism than saturated fats with the same number of carbon atoms. Saturated fats can stack themselves in a closely packed arrangement, so they can freeze easily and are typically solid at room temperature. For example, animal fats tallow and lard are high in saturated fatty acid content and are solids. Olive and linseed oils on the other hand are highly unsaturated and are oily.
Animal fats and oils are lipid materials derived from animals. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides. Although many animal parts and secretions may yield oil, in commercial practice, oil is extracted primarily from rendered tissue fats obtained from livestock animals like pigs, chickens and cows. Dairy products also yield popular animal fat and oil products such as cheese, butter, and milk.
Flesh and animal fat have a melting temperature of 184°C, a boiling point of around 200 °C and an ignition point of 280°C where it will burst into flames without spark. Certain substances such as goose fat produce a higher smoke point than other animal fats, but are still lower than many vegetable oils such as olive or avocado.
Animal fats are commonly consumed as part of a western diet in their semi-solid form as either milk, butter, lard, schmaltz, and dripping or more commonly as filler in factory produced meat, pet food and fast-food products. Dairy products are animal secretions which contain varying levels of water, oils, fats and animal cells from circulatory and lymphatic systems such as blood and mammary glands.
A vegetable oil is a triglyceride extracted from a plant. Such oils have been part of human culture for millennia. The term "vegetable oil" can be narrowly defined as referring only to substances that are liquid at room temperature, or broadly defined without regard to a substance's state of matter at a given temperature. For this reason, vegetable oils that are solid at room temperature are sometimes called vegetable fats. Vegetable oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure. Although many plant parts may yield oil, in commercial practice, oil is extracted primarily from seeds.
On food packaging, the term "vegetable oil" is often used in ingredients lists instead of specifying the exact plant being used.
See also individual commodity headings and Bulk Oils and Fats.