Canola oil, also called rapeseed oil, is generally in deep yellow or brown color. Canola oil contains 0.4-1.0% arachidic acid, 14-19% oleic acid, 12-24% linoleic acid, 31-55% erucic acid, 1-10% linolenic acid, etc. All these unsaturated fatty acids and vitamin E can be absorbed by human body well, and are good to soften blood vessels and delay senescence. From nutritional value aspect, as high as 99% rapeseed oil can be absorbed by human body, and it is good to gallbladder function. Even when the liver is in pathological conditions, rapeseed ketone can be metabolized by human body normally.
There are mainly 2 methods for canola oil production: pressing method and extracting method. In recent years, oil extraction method develops fast, which is based on organic solvent extraction principle and can significantly increase oil yield. Advanced pre-pressing & extraction method include flaking, steam cooking, pre-pressing and solvent extraction, that is, to press 18% to 19% oil by oil press, then the pre-pressed oil cake is processed by solvent extraction, so that the oil residue of dry oil cake can be decreased to 2% to 3%.
The oil yield of pre-pressing & extraction method is much higher than sole pressing method, but the canola oil produced by pre-pressing & extraction method contains lipid peroxide, colloid and isothiocyanate that can affect oil taste and quality. Besides, it also contains free fatty acid that influences canola oil storage. Therefore, most canola oil manufacturers still adopt screw oil pressing method.
Common screw oil presses produce 4-6kg less rapeseed oil per 100kg rapeseed than extraction method, and the crude oil quality is poor. For improving oil yield, canola oil processing must adopts high pressure and steam cooking temperature.
1.Pre-treatment: the aim is to improve oil seeds shape, so that the oil is pressed from oil seeds fast. Main purposes: 1. Give oil seeds certain plasticity; 2. Reduce refined oil stickiness; 3. Bind protein; 4. Remove oil seeds biological activity; 5. Detoxify.
2.Cleaning: good pre-treatment begins from cleaning, which is to remove the sand, stone, stem, leaf, etc. from canola oil seed. Seed cleaning is quite important, it can on one hand assure product quality (oil and cake), on the other hand prevent wearing of pre-treatment equipments.
Heat treatment, that is steam cooking: heat treatment is one way to increase canola seed oil yield; it is also an important procedure in oil plant.
3.Canola oil pressing: as canola oil seed is different from other oil seeds, the worm and barrel of canola oil press shall be different. In production, the worm is required to present sawtooth shape curve and cone, which is benefit for fully destroy the molecules of oil seeds and produce oil to the largest extent.
4.Canola oil refining:Rapeseed oil refining mainly include hydration, alkali refining, bleaching and deodorization process, etc. Hydration means to remove or recycle the hydrophilic phospholipid from rapeseed oil, also called dephosphorization. Alkali refining is to purify crude canola oil, which is to add caustic soda solution to the crude oil, and then use centrifuge for separation. Decolorization is to decrease pigment content of rapeseed oil to the required level, it mainly utilizes certain amount of clay to mix with heated oil under nitrogen environment, then decolorize in decolorization tank. Deodorization is to destroy peroxides in oil, remove aldehyde, ketone or other air oxidation generated odorous substances that are more easily volatile, and can damage the instable carotene to lighten canola oil color.