The seed or grain of oilseed crops contains about 20–50% oil, up to about 70%,
which is extracted either by physical pressure or by solvent extraction—normally
using hexane—or a combination of both methods. The oil is mainly used for making
cooking fats and margarines, though linseed and castor oil are not edible and so are
mainly used in industry.
Most vegetable oils are unstable, and the glycerides in the oil break down after
some time, making the oil rancid. Three types of oil are extracted from plants:
- Non-drying, where the oil is mainly glycerides of saturated acids, and which
remains a liquid and does not form a surface film when exposed to air.
Examples include castor, grape, groundnut, olive and oil palm. - Drying, which can form an elastic film when in contact with air, and which
have glycerides of the unsaturated type. Examples include linseed, safflower,
soybean and tung (Vernicia fordii). Safflower and soybean are sometimes
classified as “semi-drying”.
Semi-drying, which together with drying oils are important in industry, for the
production of paint, varnish, soap, detergent, etc. Examples include cottonseed,
Niger seed, maize and sunflower.
Average Oil Yields
Yields of oil vary enormously, but palm-oil is generally considered to be the highest
yielder, and sesame the lowest. Approximate average yields, in kg/ha, are as
follows: palm-oil 1000, safflower 500, groundnut 270, sunflower 225, olive and
soybean 200, sesame 150.
Minor Oil Crops
Safflower (Carthamus tinctorius). Widely grown in parts of North and South
Africa, India, China, North America, Canada and Australia. Almost 70% of global
production is grown in North America. Produces a drying or semi-drying oil; some
types are rich in linoleic (polyunsaturated) acid, others are rich in oleic acid
(monounsaturated).
Tung/Mu-Tree/Noix d’abrasin (Aleurites montana). A perennial tree grown in
China, Paraguay, Argentina and Malawi. Produces a drying oil.
Buffalo Gourd (Cucurbita foetidissima)—described in 2G, page 273.
similar to sperm whale oil, which withstands extreme pressure.
Other oilseed crops include rape, cotton, olive and coconut.
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Jojoba/Goat Nut (Simmondsia chinensis). A drought resistant evergreen shrub
0.5 1.5 m tall that produces beans with about 40% oil that is highly valued in industry,