|Infobox on Oil Seeds
|Example of Oil Seeds
|Stowage factor (in m3/t)
|Humidity / moisture
Description / Application
A seed oil is a vegetable oil that is obtained from the seed (endosperm) of some plant, rather than the fruit (pericarp).
Most vegetable oils are seed oils. Some common examples are Sunflower Oil, canola oil, and sesame oil.
Some important vegetable oils are not seed oils. Some examples are olive oil and peanut oil.
|Grape seed oil
|Palm kernel oil
|Tonka bean oil
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.
To produce vegetable oils, the oil first needs to be removed from the oil-bearing plant components, typically seeds. This can be done via mechanical extraction using an oil mill or chemical extraction using a solvent. The extracted oil can then be purified and, if required, refined or chemically altered.
Oils can also be removed via mechanical extraction, termed "crushing" or "pressing." This method is typically used to produce the more traditional oils (e.g., olive, coconut etc.). There are several different types of mechanical extraction. Expeller-pressing extraction is common, though the screw press, ram press, and Ghani (powered mortar and pestle) are also used. Oil seed presses are commonly used in developing countries, among people for whom other extraction methods would be prohibitively expensive; the Ghani is primarily used in India. The amount of oil extracted using these methods varies widely, as shown in the following table for extracting mowrah butter in India:
The processing vegetable oil in commercial applications is commonly done by chemical extraction, using solvent extracts, which produces higher yields and is quicker and less expensive. The most common solvent is petroleum-derived hexane. This technique is used for most of the "newer" industrial oils such as soybean and corn oils.
Supercritical carbon dioxide can be used as a non-toxic alternative to other solvents.
Oils may be partially hydrogenated to produce various ingredient oils. Lightly hydrogenated oils have very similar physical characteristics to regular soy oil, but are more resistant to becoming rancid. Margarine oils need to be mostly solid at 32 °C (90 °F) so that the margarine does not melt in warm rooms, yet it needs to be completely liquid at 37 °C (98 °F), so that it doesn't leave a "lardy" taste in the mouth.
Hardening vegetable oil is done by raising a blend of vegetable oil and a catalyst in near-vacuum to very high temperatures, and introducing hydrogen. This causes the carbon atoms of the oil to break double-bonds with other carbons, each carbon forming a new single-bond with a hydrogen atom. Adding these hydrogen atoms to the oil makes it more solid, raises the smoke point, and makes the oil more stable.
Hydrogenated vegetable oils differ in two major ways from other oils which are equally saturated. During hydrogenation, it is easier for hydrogen to come into contact with the Fatty Acids on the end of the triglyceride, and less easy for them to come into contact with the center fatty acid. This makes the resulting fat more brittle than a tropical oil. The other difference is that trans fatty acids (often called trans fat) are formed in the hydrogenation reactor, and may amount to as much as 40% by weight of a partially hydrogenated oil. Hydrogenated oils, especially partially hydrogenated oils with their higher amounts of trans fatty acids are increasingly thought to be unhealthy.
In the processing of edible oils, the oil is heated under vacuum to near the smoke point, and water is introduced at the bottom of the oil. The water immediately is converted to steam, which bubbles through the oil, carrying with it any chemicals which are water-soluble. The steam sparging removes impurities that can impart unwanted flavours and odours to the oil.
Shipment / Storage / Risk factors
Oil seeds are used for the extraction of oil and shipped in bulk, or in bags. Small changes in moisture content dependent on the condition of the atmosphere will not normally cause damage to oilseeds. If, however, seeds are stored in a confined space, the lack of ventilation may lead to heating and sweating and evaporation may be excessive in parts of the seed with condensation in other parts, leading to local mould growth. This will lead to rapid increase in free fatty acid content of the oil. In the early stages seeds stick together and form lumps, which break up easily unless the damage has become severe, when a bag of seeds may become a solid block. Claims may be put forward on the ground that there has been a high increase in acid value or ‘free fatty acid’ in consequence of decrease in oil content. This type of loss may be partly attributable to the nature of the seed itself, i.e. quality (green), unfavourable weather at the time of harvest, insufficient drying etc. The analysis on out-turn of both sound and damaged seeds should be checked as a guide to assessment of allowance. If seeds are wet and mildewed the oil extracted may not be seriously damaged or not damaged at all, as there is not an increase in acidity. Chemical tests should be carried out to determine the damage, if any. Damage may also take the form of heating or bacteria activity causing hot spots, fermentation and, in some cases, loss in weight. Heating in storage will lead to mould growth and, in some cases where the temperature is high, scorching of the seed will be obvious. Insect attack is more common with groundnuts than with Palm Kernels, and may be recognised in the case of nuts in shell by the entry holes, and in kernels, by numerous holes and the presence of larvae. Insect damage as well as heating results in increased fatty acid. With insect damage, an intense attack will be denoted by the presence of a quantity of fine metal associated with the kernels. Normally there is no danger of loss of colour in groundnuts and palm kernels during transit. They may, however, be discoloured due to damage by one of the other causes indicated above. Loss of weight can occur due to the loss of moisture or to extensive insect infestation. The former is only determined by an analysis of the seed. It depends on the humidity at the time of weighing, as there is an equilibrium moisture take-up of the seed dependent on atmospheric conditions. If the nuts are loaded under conditions of high humidity there is every possibility that they will lose weight in transit.
See also individual commodity headings.