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: 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.
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.
Level one and two soybean oil are yellowish or colorless, clear and transparent.
Level three and four soybean oil is yellow or brown, but having the smell and taste of soy itself, that is, we often say that the bean flavor.
Soybean oil has a discoloration process, so that the level three and four soybean oil have deeper color.
As the process complex, with the same brand soybean oil level one and two are more expensive than level three or four.
No matter which level of oil, as long as they meet national standards, they are healthy.
Although level one and tow oil with high refining degree, they lost a lot of nutrients, such as soybean oil carotene which will be lost in the process of discoloration.
Level three and four edible oil have higher levels of impurities, but also retained some carotenoids and other nutrients beneficial to human body composition.
Thus, according to the individual needs of different, choose different levels of cooking oil.
Soybean oil contains monounsaturated fatty acids of about 24%, polyunsaturated fatty acids high, about 56%, a relatively high vitamin E content. It is unstable at high temperatures, is not suitable for high temperature frying, and therefore are often processed into salad oil and the like.
Peanut oil fatty acid composition is more reasonable, containing more than 40% of monounsaturated fatty acids and 36% unsaturated fatty acids, rich in vitamin E. Its thermal stability is better than soybean oil, used for everyday cooking, but not suitable for frying. Easily contaminated peanut aflatoxin, produced strong carcinogen aflatoxin, so be sure to select the best quality peanut oil.
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