Oxygen in the air let the oil change quickly, especially as soybean oil, sunflower oil, a relatively high degree of unsaturated edible oil, more easily oxidized once exposed will have a “restless factor” – free radicals, it series of reactions will occur, so that further oil oxidation. Once this process occurs, it got out of hand, its index oxidation process is peroxide value. Initial segment of oil oxidation is quiet, colorless and tasteless. After intermediate oxidation and decomposition, will see a slight sniff “does not taste fresh.” Continued reaches a certain level, it becomes aldehydes, ketones, acids and other substances with a clear “rancid taste” of small molecules. This is called oil “rancid.” The higher the degree of rancidity, peroxide value level will be higher.
Advantages: rapeseed oil fatty acid composition ratio is closest to human needs. Low content of saturated fatty acids, low erucic acid rapeseed oil, high oleic acid content, the ratio of essential fatty acids linolenic acid after linseed oil. Secondly, rapeseed oil containing sterol beneficial to the body. Sterols reduce cholesterol, reduce cardiovascular disease, cancer and other physiological functions. Finally, the high content of polyphenols, polyphenols have lower cholesterol, free radical scavenging, anti-tumor and other biological activity, it is a natural source of antioxidants. In addition, canola oil is also rich in vitamin E, carotenoids and selenium, iron and other trace elements.
Disadvantages: erucic acid rapeseed oil contains detrimental to human, animal kidney cholesterol can lead to long-term intake will affect growth and development. China has now realized cole “double low” quality improvement, namely erucic acid content, low glucosinolate content. Therefore, we do not have to worry about eating high erucic acid rapeseed oil.
Eat oil Recommendation: rapeseed oil to be eaten as soon as possible after opening the bottle, place too long, one of the polyunsaturated fatty acids can easily be destroyed oxygen in the air oxidation, produce substances detrimental to human body. Fortunately, rapeseed oil is also rich in vitamin E, can enhance the antioxidant effect, make a variety of unsaturated fatty acids from oxidative deterioration. But still recommended to buy a small bottle, finished as soon as possible after purchase.
Advantages: linoleic acid in soybean oil is dominated, contain small amounts of α- linolenic acid, saturated fatty acid contains very little. Linoleic acid to reduce the risk of heart disease limited role, but α- linolenic acid is more beneficial. Clinical nutrition experiments confirmed that trigger coronary heart disease risk factors, in addition to high levels of cholesterol, the other two factors is high blood pressure and blood clots, linolenic can exactly reduce these two factors. Vitamin E is abundant in soybean oil.
Disadvantages: Because linoleic and linolenic acid are not heat-resisting, linolenic acid in particular, after frying or repeated heating are easily oxidized polymerization, very harmful to health.
Recommendations: soybean oil is best used for low-temperature cooking, such as making pasta, soup, stew and transfer stuffing, etc., should not be prolonged high temperature frying food. Corn oil, sunflower oil, wheat germ oil and soybean oil fatty acid composition similar. If you usually eat a lot of soy products, soy bean oil substances already ingested, polyunsaturated fatty acid intake is adequate, it is not necessary to use every day, soybean oil, sunflower oil, corn oil to cook, you can use olive oil , tea seed oil, peanut oil, rice bran oil fatty acid containing more monounsaturated fat for cooking.
When buying oil, to see the date of manufacture, try to buy the production date close, because the oil in the storage process will be slow oxidation.
After bought vats of oil, poured oiler them, and then immediately put the lid twist reality. Do not directly put to use when cooking for each barrel of oil, which means that every day a lot of new oxygen into oil drums.
Oiler in the amount of stored oil should be eaten within a week. Buy the best that can be screwed on the lid or a lid oiler oil bottle, do not put oil on the open mouth of the container.
Oil must be placed in a dark, cool place, do not let them be affected by sunlight and high temperatures.
Grease color change in the use, called in the industry grease anti-color or back color. In general, the anti-color does not affect its food value.
Effect of vegetable color reversion many factors: pigment, metal ions, light, oxygen, temperature, natural antioxidants (tocopherol) oxides, fatty acid oxides.
On the one hand, corn oil is a byproduct of corn deep processing, the process is much more complicated than soybean oil, crude corn oil have high acid, impurities, the iron ions are also much higher than soybean oil, if refined removal is not complete, it is easy to lead to poor quality stability, iron ions itself is not harmful, but having a catalytic activity, can accelerate fat oxidation and rancidity and other metamorphic processes.
On the other hand, corn germ oil, unsaturated fatty acids, high tocopherol content of the oil as the main features of the health indicators, are more prone to reversion phenomenon, usually around 32 degrees in summer temperatures, oil color changes difference within 3 days is very significant.
Camellia oil have low fat, good taste, easy to digest.
Crude camellia oil refers to the origin of the traditional indigenous methods to extract only after a simple filtering process tea seed oil.
Indigenous virgin tea oil mainly primary crushing by family workshops. In production process, just by the simple process of drying, crushing, pressing, filtration, etc., so squeezing out tea seed oil contains more impurities, just semi-finished or “crude oil.”
While oil press through advanced technology processing crude oil, then after cleaning, deacidification, deodorizing, degreasing and a series of strict procedures refining complex produced by the tea before they call “refined tea oil,” camellia oil after refining is better, save the tea itself rich nutritional value and trace elements.
Now edible oil is divided into four grades, grade one oil is said salad oil before.
The difference is that process: whether decolorization and deodorization.
The two are not good or bad.
Choose which grade of oil according to your own needs, and not simply judged by the quality grade of oil.
Grade one soybean oil have light color, high smoke point, no taste, fewer impurities, more pure, but at the same time less nutrients.
Grade three soybean oil has not been decolorized and deodorized, reducing possible contamination of clay and the loss of vitamin E, color depth, it retains some peculiar smell of soybean oil.
Although there are some so-called impurities, but retain more nutrients.
Both have strengths and weaknesses.