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Canola which is a genetic variation of rapeseed has become one of the most important oilseeds in the world production. Canola once considered as a specialty crop in Canada, has become a major cash crop in North America. Due to its very low saturated fat and high monounsaturated fat content, canola oil has been claimed to promote good health, even the beneficial effects of omega-3 fatty acids helps to prevent cardiovascular diseases. Extraction of canola oil can be done mechanically with a traditional oil press or using the principles of solvent extraction. More recently environmental friendly techniques like supercritical fluid extraction is gaining importance for the separation of oil. This paper reviews the biological and chemical aspects of canola, its extraction, byproduct utilization and the potential health benefits.
Key words: Canola, solvent extraction, canola meal, health benefits.
Biological and chemical aspects of canola
Extraction and purification methods
Uses of Canola meal
Potential health benefits
Global canola production has increased rapidly over the past 40 years. Canola production was 10-14 percent of world oil crop production between marketing years 1998/99 and 2007/08 . In early 1956, the U.S. Food and Drug Administration (FDA) banned the human consumption of rapeseed oil due to the presence of erucic acid and glucosinolates in the seed. Further extensive research lead to the development of a new variety of rapeseed eliminating the above concerns in 1970s. The Western Canadian Oilseed Crushers Association registered these varieties with the name "canola" in 1978 for marketing reasons. China and India are considered to be the minimal consumers of rapeseed oil, but however low erucic acid rapeseed production in China is increasing and reached nearly 50% of total production of oilseeds in that country in 1998 
The principal objective of canola processing is to remove the oil from the seed and to process that oil to a final product for use as edible oil for human consumption. Also, the solid portion of the seed can be processed to provide an edible meal product which can be used as a high-protein supplement in animal feeds . Due to the large varieties of species with different seed structure and characteristics, and the glucosinolate contents, the processing of the seeds has become a challenge for the industry. Solvent extraction can be used as an effective method for the oil extraction. The commonly used solvent for extraction is hexane or hydrocarbon mixtures rich in hexane. Supercritical (SC) carbon dioxide (CO2) extraction is gaining more importance in the recent years due to several advantages that include, inertness, non flammability, environmental compatibility, easy removal of the "solvent" from the analyte [3,4] and reduced cost (depending upon CO2 purity) [3,4,5]
Canola meal is the second most widely traded protein ingredient after soybean meal representing a 12.40% of the world protein meal production (207 million metric tons in 2004/2005 ). Canada is one of the major producers and users of canola meal having an area harvested, yield and production of approximately 5.24 million ha, 1.72 t/ha and 9.00 million metric tons, respectively in the season 2006-2007 .
Canola has many potential health benefits due to the presence of significant amounts of essential fatty acids and antioxidants. The United States Food and Drug Administration (FDA) has approved the health claim for canola oil for reducing the risk of coronary heart diseases 
Biological and chemical aspects of canola (Brassica napus L.)
Canola in the family of Brassicaceae (also known as oilseed rape) is classified as a soft oilseed. The seeds are small and generally rounded (approximately 250 to 500 seeds per g) and possess thin and difficult to remove hulls (testa). Seeds usually contain about 35 - 45% oil and 18 - 23% crude protein.
For the cultivation of canola crop, there should be at least 127mm of standing water. On an average 6.9 to 7.2 kg of canola seed is produced per hectare . The time of plant growth and development is effected by the sowing date, which helps the plant to better survive under the stress of heat and drought . Studies have showed that the sowing date may influence the fatty acid composition through improving ontogenesis and that a late sowing date decreases the oleic acid and increase the linoleic acid content of the seed. The quality of canola seed oil is effected by the interaction of genotypic and environmental parameters [11,12].The amount of unsaturated fatty acids of the seed is very much under the influence of environmental parameters during the period of oil accumulation and seed maturity [13,14] The effects of different sowing dates and canola varieties on the oleic acid and palmitic acid content of canola oil is shown in Table 1 .
Table 1 The effects of different sowing dates and canola varieties on the oleic and palmitic acid content of canola oil, respectively.
Palmitic acid % (16:0)
Mean values, followed by the same letters in each column are not significantly different (Duncan multiple range test at 5% (Adapted from (Omidi et al., 2009))
It is important to indicate the aim of canola production before planting, as strategies used for increasing the oil content of the seeds may inversely effect the protein concentration and vice versa.
The amount of erucic acid present in canola is <1%, whereas in rape seed it is approx 45%.
Canola has the highest level of unsaturated fats among the edible oils. It has a saturated fat content of 7%, polyunsaturated fat contents (linolenic acid- 21%, alpha-linolenic acid- 11%) and monounsaturated fat (oleic acid) of 61% .
Extraction and purification
For oilseeds with high oil content, such as rapeseed and canola, a combination of pressure and solvent extraction is used to remove the oil from the seed (Fig. 1) . The extraction and purification procedures are discussed bellow.
Fig. 1 General flowchart for canola prepress solvent extraction technique 
Primary processing 
After the initial removal of the foreign materials that will affect the quality of the product, the seed is cooked at a temperature of 30 - 40 0C to avoid the seed shattering in the flaking process. The seeds are flatten to a thickness of ~ 0.25 mm through flaking rolls which will helps the rupture cells to free the oil and make it easier for the solvent percolation through the seed. In order to inactivate enzymes that might cause problems during later processing steps the flaked seeds are usually cooked in stack cookers with temperatures reaching as high as 90 0C.
After cooking, the seed flakes are passed through a screw press, known as an expeller, which squeezes out ~70% of the oil which is routed to a settling tank. The cake is sent to the solvent, (normally hexane) in which the solvent dissolves the oil from the canola meal. The canola cake leaving the extractor has typically less than 1% oil content and is known as ''white flakes''. Further distillation is used for separating the solvent from the meal.
Secondary Processing 
Secondary processing of the oil (Fig. 2), called as refining, is necessary to make the oil suitable for functional uses by removing the undesirable fractions. Degumming (or Desliming) is a process which involves the washing of oil with water (which contains other ingredients such as phosphoric acid or metal-sequestering agents) for precipitating phospholipids (lecithin or gums) from the oil.
The refining process is necessary to remove the free fatty acids from the oil, which may impart an unpleasant metallic taste to oils. Caustic refining and physical refining, are currently used to remove free fatty acids. Caustic refining is mainly used, as physical refining cannot be carried out successfully on oils with high levels of phosphorus and acid degumming is a prerequisite for the process. In caustic refining, the oils are first treated with concentrated phosphoric acid and then ~ 2-3% of aqueous sodium hydroxide (caustic soda) solution.
Bleaching process is carried out to remove the color bodies, particular chlorophyll, iron and some oxidation compounds. It is done by mixing the oil with 1-3% of an absorbing solid, usually diatomaceous earth or bleaching clay.
Hydrogenation is done to prevent the oxidation, especially when the oil is heated to frying temperatures. It involves treatment of the oil with hydrogen in the presence of a catalyst under controlled pressure (100 -300 kPa) and temperature (160-200 0C)
Inter-esterification is used to prepare nonhydrogenated canola oil. The liquid canola oil may be inter-esterified with a harder fat such as palm oil or a fully hydrogenated vegetable oil. Addition of a catalyst like sodium methoxide to the oil results in the formation of new triglycerides with different properties.
Winterizing or dewaxing is used to remove waxes and fully saturated triglycerides present in small amounts in the oil. It may precipitate or haze when the oil is stored at refrigerator temperature.
Deodorizing is used to remove the small amounts of volatile flavor components, low levels of free fatty acids, some sterols and more importantly the antioxidant tocopherols. A distillation process known as deodorization is used to remove these compounds, during which the oil is treated with steam (2-4%) at high temperature (260-265 0C) and low pressure (2-4mm Hg).
Formulation is used to improve the product shelf life. Shelf life can be improved by the addition of small amounts of citric acid or antioxidants or else the deodorized oil may be bottled directly.
Fig. 2 Secondary processing of canola oil. 
Standard methods for the determination of oil content include supercritical fluid extraction (SFE) [17, 18] (which is more environmental friendly), nuclear magnetic resonance (NMR) [19, 20, 21] and near infrared spectroscopy (NIR) [22, 23]. NMR and NIR are very fast and nondestructive, but have a disadvantage in both these methods as it requires an intensive calibration by solvent extraction methods. The oil contents of soybean, rapeseed and sunflower determined by different extraction methods are shown in fig. 3 
Fig. 3 Oil content of three different oilseeds in respect to the different extraction procedures. DGF, German Fat Science Society standard method B-1 (87); ASE, accelerated solvent extraction; SFE, supercritical fluid extraction; fexIKA, solid fluid vortex extraction; MAE, microwave-assisted extraction.
The protein-rich meal that results after the oil extraction from canola seed is currently gaining more interest, especially in livestock and aquaculture based industries, due to its high nutritive value. Canola meal is a good source of protein for animals and is a particularly rich source of sulphur amino acids, methionine and cystine [25,26] It has a protein content of 35-36 g/100 g and crude fiber content of 12 g/ 100 g . It is also reported that canola meal is a relatively a good source of essential minerals especially potassium, sulphur, calcium and iron, as well as a good source of selenium and phosphorus. It has the highest protein efficiency ratio (PER = 3.29) of all plant based proteins . PER is a commonly used measure for protein quality. A comparison of proximate chemical compositions of canola soybean and flaxseed meal is shown in Table 2. 
Table 2 Proximate chemical composition (g/100 g) of selected meals.
11.35 Â± 0.18a
11.56 Â± 0.06a
6.65 Â± 0.10b
2.77 Â± 0.08a
1.59 Â± 0.04c
2.17 Â± 0.07b
48.29 Â± 0.44a
38.96 Â± 0.14b
6.26 Â± 0.11b
6.53 Â± 0.06b
7.01 Â± 0.07a
11.54 Â± 0.30a
3.50 Â± 0.14c
5.27 Â± 0.06b
43.31 Â± 0.87b
40.10 Â± 0.48c
46.60 Â± 0.06a
Means Â± standard deviation (SD). NFE = Nitrogen-free extract. Values in the same row followed by similar superscript letters are not significantly different at p â‰¤ 0.05. (Adapted from (Khattab and Arntfield, 2009))
Due to the presence of some anti nutritional factors the use of canola meal is restricted to human nutrition. It contains approximately 16 mmol/g total glucosinolates which are well known for their toxic effects at high doses in humans. Also 1.5-3.0 g/100 g tannins, 0.6-1.8 g/100 g sinapine and 3.0-6.0 g/100 g phytic acid . Heat treatments were reported to remove the anti nutritional factors of canola meal [30, 31]. Desulfation and capillary gas-liquid chromatography has been used for quantitation of glucosinolates . Also the application of organic solvents can remove the glucosinolates fractions from the meal .
Canola meal is a good organic fertiliser with good amounts of nitrogen, phosphorus and sulphur. Recent advances in the researches indicate that the canola meal has the potential for use as an adhesive and as a surfactant in the industries . The extraction of protein from the meal, its separation and modification processes, for producing value-added components from canola meal are still being developed
Canola oil is high in healthy unsaturated fats (approx 93%) and has low amounts of saturated fatty acids (7% or less) . From Table 3  it can be seen that canola oil has significant amounts of essential fatty acids. Oleic acid is effective in lowering plasma cholesterol levels, whereas linoleic and lino-lenic acids are effective in managing physiological reactions ranging from blood clotting to immune response. 
The Food and Drug Administration (FDA) has ruled that canola oil has the potential to prevent the risk of coronary heart disease due to its unsaturated fat content. The FDA puts all health claim petitions through rigorous scientific review. The qualified health claim about canola oil is 
''Limited and not conclusive scientific evidence suggests that eating about one and a half tablespoons (19 grams) of canola oil daily may reduce the risk of coronary heart disease due to the unsaturated fat content in canola oil. To achieve this possible benefit, canola oil is to replace a similar amount of saturated fat and not increase the total number of calories you eat in a day.''
The relatively high level of oleic acid combined with the low level of total saturated acids would be responsible for the cholesterol- lowering effect of canola oil in humans . A pilot study in patients with peripheral arterial occlusive disease showed that the Canola oil decreases cholesterol and improves endothelial function. 
The risk of atherosclerosis is reduced by the high level oleic type acid in canola which may have a protective effect against oxidation of LDL. Also the use of canola oil in infant formulas has been proposed mainly because of its relatively high oleic acid level and the balance between n-3 and n-6 fatty acids (18:3/ 18:2 ratio of 1:2). . Canola is also a good source of the natural anti-oxidants and tocopherols. It is mainly rich in Î±- isomer which is considered to be the most biologically active form. (Table 4) 
Table 3 Comparison of major fatty acids in traditional and modified vegetable oils
Fatty acids (% of total)
(Adapted from McDonald and Fitzpatrick)
Table 4 Amount of tocopherol present in selected vegetable oils (ppm)
(Adapted from Eskin et al.)
Canola is a good source of of sterols including the rare brassicasterol (Table 5) . The most abundant phytosterols (Î²-sitosterol, campesterol, and sigmasterol) have been used in medicine recently due to their therapeutic effects and low-toxicity in humans and animals. Clinical studies have proved that the intake of phytosterols will reduce serum or plasma total cholesterol and low-density lipid cholesterol levels in normal and mildly hypercholesterolaemic subjects. Phytosterols are also effective in the treatment of prostatic hyperplasia, rheumatoid arthritis, allergies, and stress-related illness and it even inhibits the development of colon cancer. 
Table 5 Amount of sterols present in selected vegetable oils (%)
Total (mg/100g of oil)
Adapted from Eskin et al.
The consumption of canola oil is increasing rapidly in many countries due to the presence of more unsaturated fatty acids which offers potential health benefits to humans. Canola meal, a by-product of canola processing is used as a high-protein feed ingredient in the rations of poultry, swine, cattle and fish. The extraction of canola oil mainly involves two overall processes, mechanical pressing and extraction using a solvent. There has been considerable research into the use of enzymes to break down cell walls allowing the seed to be processed. Also the extraction process using supercritical fluids is gaining more importance due to the significance of green technologies in the present scanerio. But more research must be carried out to make the extraction techniques more environmental friendly and economical.