Plant oils: raw material produced by plants using soil, water, wind and sun.
They are one of the main groups of raw renewable materials produced by crops and transformed with low environmental impact and low-energy processes.
Plant oils are mainly made of lipids, triglycerides in most of the cases. Besides the lipids they may also contain small water percentages (generally less than 2%), or minor saponifiable (like phospholipids, sphingolipids and waxes) and unsaponifiable components. To this group belong saturated, unsaturated and polyunsaturated hydrocarbons, tocopherols, tocotrienols, superior aliphatic alcohols, sterols, metilsterols, diterpenic and triterpenic alcohols, phenols, liposoluble vitamins A, D, K, E or other pigments like carotenoids, chlorophyll and ubiquinones.
In addition, plant oils are easily soluble in organic solvents and difficultly soluble in water.
Plant oils contain organic compounds with chemical classes (like double bonds and ester groups) that can easily react with other substances and chemical compounds. The consequent typical feature is the “drying”: liquid oils react with the air oxygen at ambient temperature and become resinous, hard and insoluble substances.
Drying plant oils are commercially and technically divided according to their origin:
- Linseed oil, the most used and the most typical is the Linseed oil. It is extracted from Linum usitatissimun seeds, which contain it in a percentage from 32 to 43%
- Wood oil, also called China wood oil or Tung oil, is extracted from mountain Aleurites (M Type). Both vegetable species grow spontaneously in China, but their cultivation has successfully started also in some areas in USA, South America and South Africa.
- Soy oil is extracted from the max Soy seeds, a leguminous plant from Eastern Asia but widely spread also in other continents (mostly in North America). Its content of soy oil ranges between 13 and 23%
- Tall oil (from Swedish tallo ja= pine oil), is a sub product of paper fabrication, treating wood pulp in the sulphate process.
- Perilla oil is extracted by the Perilla ocymoides or Perilla frutescens seeds. Both plants are grown in Japan, China and India.
- Sunflower oil is obtained by Helantius annuus seeds, a plant from Mexico spread in all regions with tempered and warm weather, especially in some areas of Russia.
- Safflower oil is extracted by Carthamus tinctorius, that contain it at 27 to 36%. This plant comes from Himalaya and is now cultivated in the USA.
- Oiticica oil is extracted from Licania rigida seeds. It is widespread in Brazil and cultivated in the USA as well.
The majority of drying plant oils is industrially produced extracting the seeds from the plants in two ways: discontinuous or continuous pressing and solvent extraction.
In the pressing method the seeds undergo mechanical cleaning through fans, sieves and electromagnets and then are shelled (if necessary) and milled normally in roller mills. The flour is preheated between 80-100° and pressed between two plates of a hydraulic press. In this way we obtain the oil contained in the seeds.
In the discontinuous method, the preheated flour is put on a continuous press and pressed against the wall of a horizontal cylindric cage by an endless screw equipped with helical blades and profiled in order to exert a progressively increasing pressure. At the end the oil comes out from the small cage holes.
After the continuous or discontinuous pressing the oil is filtered to separate the solid suspended particles.
In the second method, after the mechanical cleaning the seeds are reduced in flakes. These need to be as thin as possible, then they are put in an extractor with a solvent.
They mostly work continuously and there are several types, for example some of them combine the solvent treatment to the mechanical pressing.
The most used are the hexane and the supercritical carbon dioxide. The solvent extraction has higher performances than pressing and for this reason it is more used.
Plant oils are recognized as essential nutritional substances in human and animal diets.They supply a concentrated source of energy, essential fats (prostaglandins) and give a strong feeling of satiety after their consumption. Moreover, they supply also liposoluble vitamins and are used to produce tastier foods. Oils are present in different quantities in many foods.