After being harvested, peanuts are dried approximately two to four weeks, allowing the water content during this time to be reduced from about 40% to around 5 to 7%. Finally the peanuts, which have a fat content of around 45%, are removed from their shells. This is achieved primarily using disc mills or corrugated rolls. In order to acquire the oil from the seeds, they first need to be cleaned over strainers, crushed on roller mills, and pressed in a screw press / oil press (cold pressing). Should the residual content of the oil, which would otherwise remain in the press cake, is to be obtained as well, then this is achieved using an extraction with hexane.
Traces of aflatoxins that have gotten into the oil can be inactivated through a neutralizing process involving alkali treatment. Cold-pressed and extracted peanut oil are furthermore easily bleached and deodorized with activated charcoal. In addition, partial hydrogenation turns peanut oil into arachidis oleum hydrogenatum (hydrogenated peanut oil), enabling it to be further processed.
Characteristics and shelf life
Peanut oil and African peanut oil are to be distinguished from one another. Peanut oil has a slightly yellow hue, whereas refined peanut oil consists of a white, greasy-feeling mass. The African variety forms a colorless to yellowish liquid. Cold-pressed peanut oil possesses a slight to distinct note of peanut and smells slightly fruity and rusty. Hydrogenated peanut oil, meanwhile, is almost odorless. African peanut oil likewise features peanut tones, and tastes rather mild and nutty. Peanut oil after the initial cold-pressing still has a very pleasant taste, yet the refined oil is nearly tasteless.
The smoke point of peanut oil is around 160° C; that of refined peanut oil, around 232° C. The melting point of peanut oil lies between -2° C to 3° C.
Peanut oils consist of triacylglycerides. However, the lipid composition of the peanut oil also varies and is dependent on where the peanuts used in the oil were cultivated. On average, peanut oils contain approximately 35 to 69% monounsaturated fatty acid and around 13 to 35% double unsaturated linoleic acid. In addition, the oil also contains saturated fatty acids such as palmitic acid (8 – 14%), stearic acid (about 1 – 4%), arachidic acid (approximately 1 to 2%), behenic acid (around 2 to 5%), and lignoceric adic (approximately 1 to 2%). Also to be found are tocopherols (various forms of Vitamin E), additional antioxidants, lecithin, hydrocarbons, and sterols. One characteristic, admittedly viewed somewhat negatively by current food science, of peanut oil is its lack of omega-3 fatty acids, and the polyunsaturated fatty acids content is relatively low.
Yet on average, it is noticeable that the lipid composition of the African peanut oils shows an elevated oleic acid content, whereas the South American peanut oil contains about the same portions of linoleic acid and oleic acid.
The advantage of peanut oil is that, unlike many other oils, it does not quickly turn rancid. When stored in a closed container in a cool, dark place, it has a shelf life of one to two years. Even if stored at warmer temperatures, it still stays fresh for months. It should be noted, however, that this oil begins turning viscous around 10 ° C, and eventually solidifies between 3 and -2 ° C.
Pharmaceutical and medical uses
In the realm of medicine and pharmacy, it is highly versatile. For example, it can be used in enemas to soften hard stools in the rectum; or to sink cholesterol levels, due to its content of unsaturated fatty acids in triacylglycerols, according to the to the Lexikon der Pflanzlichen Fette und Öle (lexicon of plant fats and oils).
In pharmaceutical technology, it serves as carrier for fat-soluble substances in external, enteral and parenteral use, especially for sexual hormones with a depot effect, and as an oil in eyedrops.
In dermatology, peanut oil is considered helpful in fighting scabs and dandruff formation in the head region. Yet it can also be used in infant care and as a bath additive for treating eczema and ichthyosis.
Additionally, hydrogenated peanut oil, due to its water absorbency, serves as an ointment base. Earlier it was a common ingredient in old prescriptive recipes, such as in camphoric ointment (an ointment which is supposed to help with muscle, joint, and rheumatic pain, or to help with colds and the flu, since it stimulates circulation and reduces pain. It is further commonly found in nasal ointments and cold balsams).
Today, however, this oil is being used less and less frequently in the production of drugs, since it still tends to become rancid, despite partial hydrogenation of the double bond in the fatty acid portion of the triacylglycerides.
In folk medicine
According to the Lexikon der pflanzlichen Fette und Öle, peanut oil is also used in naturopathy in order to treat or even heal arteriosclerosis, bladder infections, sunburns, stress, constipation, weak digestion, and orange skin after sunbathing, among other ailments.
Peanut oil is a good lubricant and is absorbed slowly into the skin. For this reason, it is readily used as massage oil in the realm of cosmetics. It makes a good base oil for massages and can thereby help release tensions in the back, remedy poor circulation, and prevent rheumatism.
Furthermore, peanut oil is used in bathing oil, or at least as an additive in bathing oil. This oil is is additionally considered good sun protection, due to its high fat content, and thus often appears in skin oils and suntan oils. As long as no peanut allergy exists, this oil is usable not only for infant and child care products, but also for skin and scalp care products. According to the Lexikon der pflanzlichen Fette und Öle, it also very good for dry or scaly skin, and for eczema.
Often this oil is used in the food industry to product margarine or to refine soups and spices.
Besides this, it can also be used for the production of soaps or coating agents.
Furthermore, a recent test has shown that peanut oil is also suitable for motor combustion.
In the kitchen
Because of its high flash point, the oil has good heat stability, making it well-suited for deep-frying and frying, for which it is used particularly often in China and Asia. Because of its low content of polyunsaturated fatty acids, it should be used sparingly as a salad dressing.
The by-product arising during oil production, the press cake, is readily further processed into protein-rich animal feed, or into soil fertilizers.
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In addition to their own knowledge acquired through press trials, the following sources were used to create the article:
- Öle, natürlich kaltgepresst, Basiswissen & Rezepte, Marcus Hartmann, Hädecke, 2008
- Heilende Öle, Pflanzenöle als Nahrungs- und Heilmittel, Neue Erkenntnisse, Günter Albert Ulmer Verlag Tuningen
- Lexikon der pflanzlichen Fette und Öle, Krist, Buchbauer, Klausberger, SpringerWienNewYork, 2008