The importance of edible oils in people’s daily life is obvious. With the development of social economy and the improvement of people’s living standards, the nutritional value of edible oils has attracted more and more attention. However, for a long time, the hygiene and safety of edible oils have not been fully understood. Some are caused by improper storage or use of oil quality changes, resulting in harmful substances in the oil; some are not refined crude oil produced by small workshops directly used for food has caused great harm to people’s health. In particular, a few illegal businesses add cheap industrial “white oil” to edible oils for profit, and consumers may even endanger their lives when they buy Edible oils. Therefore, we must pay attention to the safety and hygiene of edible oils and oils, and vigorously advocate scientific and reasonable edible methods of oils and oils. In this paper, the serious effects and damages of unrefined crude oil, reused frying oil and rancid oil on human health are discussed.
Harm of Unrefined Crude Oil on Human Health
The opening of grain and oil market has led to the emergence of many workshop-style oil mills. These small oil mills do not have large-scale production of impurity removal and refining equipment. The crude oil produced by these small oil mills directly enters the market. These oils contain a large number of impurities, moisture, phospholipids and free fatty acids. Their quality indicators are not up to the national quality standards for second-class edible oils. It damages the interests of consumers and greatly endangers people’s health.
1.Reduce the quality of edible oil and storage time
The large amount of impurities such as water and phospholipids in crude oil has a great impact on the edibility of oils. Excessive impurities will deepen the color and turbidity of oils. In cooking, due to the presence of phospholipids, oil will foam and foam a lot when heated. When frying food, it will cause “overflow pan”, seriously affecting the quality of use. In addition, the presence of these impurities will greatly shorten the storage time of oils and fats. Excessive moisture and impurities in crude oils will accelerate the decomposition and deterioration of oils and fats, increase the content of free fatty acids in oils and fats, make oils and fats deteriorate quickly, which is not conducive to the storage of oils and fats.
2.Toxic Components in Unrefined Crude Oil
Unrefined rapeseed oil has high sulfide content, which is an important factor that causes adverse effects on human body. At present, the sulfide content of secondary rapeseed oil is 150-170mg/kg, while that of unrefined crude oil is more than 200 mg/kg. The sulfide content of rapeseed oil leached from pressed cake is even as high as 1000mg/kg. Sulfides in rapeseed oil are produced by the decomposition of combed glucoside in rapeseed during oil production. These sulfides have been identified qualitatively as thiocyanates, isothiocyanates and oxazolidine copper sulfide, as well as several other sulfur compounds with relatively small content, which have not yet been completely qualitative. These sulfides are harmful to human body, such as stimulating mucosa, causing goiter, reducing growth rate, etc. They also have a pungent and stimulating odor. The smell and taste of rapeseed oil are caused by them. Therefore, sulfide can directly affect the taste, hygienic quality and nutritional value of rapeseed oil. Germany and other European countries stipulate that the sulfide content in Edible Rapeseed oil should not exceed 5 mg/kg. So far, our country has followed the standard of allowable sulfur content in rapeseed oil, which can not be said to be a defect. The sulfides in rapeseed oil can be removed by refining, so the refining process is essential for rapeseed oil.
Because of the existence of some mouldy oils, the mycotoxins in the crude oil are far beyond the standard. The moulding can also produce substances that affect the odor and taste and have great toxicity to human beings and animals. For example, peanuts are easily contaminated by aflatoxin. Aflatoxin is a kind of toxin that causes mildew in some oils. The crude oil of peanut machine contains aflatoxin. This kind of fungus can produce carcinogenic and toxic metabolites together with several other fungi, such as aflatoxin, peanut or other nut oils, and cottonseed oil. It has been proved that aflatoxin is a strong carcinogen, and peanut oil can remove the toxin as long as it is refined.
Unrefined cottonseed oil contains a lot of toxic substances. If you eat unrefined detoxified wool cotton oil, it can cause damage to the parenchymal cells, nerves and blood vessels of heart, liver, kidney and other toxic substances, and lead to acute poisoning symptoms such as dysregulation of body temperature, damage of reproductive system and decrease of serum potassium. If not corrected in time, it can lead to sudden death to the human body. The harm is great. Cottonseed crude oil can remove toxins only after refining.
Therefore, crude oil without refining is not edible. Only vegetable oil which has been refined and reached the national standard can effectively remove harmful substances and ensure food safety.
Effects of reusable frying oil on human health
In the process of frying food with oil, oil is in high temperature for a long time and is used repeatedly. During frying, oil will contact with oxygen in the air, and a series of complex chemical reactions such as hydrolysis, oxidation and condensation will occur. At the same time, the viscosity will increase, refractive index will change, color will deepen, and some volatile substances, saturated and unsaturated aldehydes, ketones, lactones will be produced. A list of physical changes produces irritating odors, in which some substances are harmful to the human body.
The changes of frying time and physicochemical indexes of edible oils and fats are shown in table. Acid value and carbonyl value are sensitive methods to test the deterioration of oil quality. Physical and chemical indexes of oil show that the quality of frying oil decreases with the increase of frying time. The longer the frying time, the greater the damage of its quality and the greater the damage to human health.
Changes of Frying Time and Physicochemical Index of Fat
The acid value, mgKOH/g peroxide,% carbonyl value, meq/kg fresh oil 0.260.090.11 frying 2 hours oil 5.160.1160.277 over standard rate 1800% 29152% frying 4 hours oil 6.0570.1080.447 over standard rate 2230% 20306% frying 6 hours oil 8.50.1210.633 over standard rate 3170% 24475%.
1.Formation of Thermal Polymers
Oils and fats can be polymerized and oxidized at high temperature for a long time to form toxic components such as cyclic polymers and glycerol dipolymers. At high temperature, the oil can also be partially hydrolyzed and then condensed into ether compounds with higher molecular weight to increase the viscosity of the oil. Thermal polymerization produces toxic substances in oils and fats, which are harmful to the health of consumers. Rapeseed oil and soybean oil with high linolenic acid content can be heated at 275 (?) C for 12-26 h to form a variety of polymers, some of which can be absorbed by the body. Through experiments on animals, it was found that animals grew slowly, their livers were enlarged and reproductive disorders appeared. Relevant experiments showed that when mice were fed with heat-polymerized oil and fed with 10% of the feed, the mice developed dysplasia and weaned. It has been reported that some deteriorated oils and fats have carcinogenic effects and their harmfulness should not be underestimated.
Studies have confirmed that heat-polymerized soybean oil has an effect on animal growth. It can make fat tissue and liver hypertrophy. Fat is heated to form a higher polymer, which can not be absorbed, and its location in the intestinal tract can stimulate intestinal inflammation. The harm to human body is relatively great.
2.Thermal oxidation reaction occurs
In the frying process, because of the contact with air and at high temperature, the oxidation and rancidity of oils and fats is faster, not only a large number of peroxides are produced, but also at high temperature, low-grade carbonyl compounds can be polymerized to form a viscous gelatinous polymer, which affects the digestion and absorption of oils and fats.
In addition, saturated fatty acids in oils and fats tend to degenerate into toxic substances at high temperatures. According to experimental studies, rapeseed oil, peanut oil or sesame oil are heated in an iron pot at 270 C for 4-8 hours, and then fed to mice in a 20% ratio. The weight gain of mice is adversely affected. The liver of mice fed with heated oil was hypertrophic, and the fat content was twice as much as that of the control group. If the mice were fed with heated oil at a rate of 30%, all the mice died within 3 weeks. At the same time, the heating oil feeding experiment at 280 C was carried out. The addition rate was 20%. Only the heating oil at this temperature was fed. Jaundice was found in the experiment, and the mice died at the sixth week of feeding, while all the mice in this group died at the third week of feeding with overheated oil.
It can be seen that the thermal oxidation of oils and fats is very harmful to human body. It is necessary to avoid excessive oxidation of oils and fats in order to ensure the safety and hygiene of edible oils and fats.
3.Producing volatile acrolein
Fried oil will hydrolyze to glycerol and fatty acid partially at high temperature. Glycerol promotes water to produce acrolein at high temperature. Acrolein has a strong pungent odor, and has a strong stimulating effect on nasal and eye mucosa. It makes the operator cough hard to bear and inhale for a long time, which will damage the respiratory system of human body and cause respiratory diseases. According to the relevant reports, the proportion of respiratory diseases among the people who had long frying operations and protective measures was 2.3 times that of the normal people.
In order to ensure the safety and hygiene of frying oil, attention should be paid to keeping the oil temperature below 200 C, and every batch of grease should be continuously used for 10 hours before replacing all the new oil.
Toxic effect of rancid oil on human body
Animal and vegetable oils deteriorate for too long or improper storage, resulting in a special odor. Gu is called “hala” odor. The deterioration is mainly due to the oxidation of unsaturated fatty acids in oils by oxygen in the air and the role of water in oils. The products produced are easily decomposed into volatile low molecular aldehydes, ketones and so on. This phenomenon is called “oil acidity”. There are two main factors for fats rancidity: one is fats oxidation, which is caused by air, temperature, moisture and metal ions in the storage environment, or air oxidation; the other is that fats are polluted by microorganisms to produce lipid oxygenase and lipid decomposition enzymes. Lipoxygenase accelerates lipid oxidation, and lipid decomposition enzymes can decompose fats into glycerol and free fatty acids. Thus, the acid value of the oil increases.
1.The nutritional value of rancid oil is greatly reduced.
The essence of rancidity of oils and fats is the oxidation process of oils and fats. During the oxidation process, the vitamins A, D and E contained in oils and fats are oxidized first. The essential fatty acids, such as linoleic acid and linolenic acid, are also destroyed. Moreover, when eating rancid oils and fats, the B vitamins in other foods are also destroyed. Therefore, long-term consumption of deteriorated oils and fats may result in the absence of essential fatty acids. Lack of poisoning and lack of fat-soluble vitamins and riboflavins can destroy the physiological balance of human body and damage human health.
2.Toxicity and disease caused by edible rancid oil
There is a large amount of lipid peroxide in rancid oil. It has been reported that poultry eating feed containing lipid peroxide can cause yellow lipid disease. After cat eating, it can cause liver, heart and kidney hypertrophy, leading to liver degeneration and fatty liver. Recent studies in molecular biology have shown that lipid peroxide is closely related to cancer, coronary heart disease and aging. Some mice were injected with methyl linoleate peroxide, only 1-2 mg, which can kill half of them. When lipid peroxide enters human body, it is easy to attack cell membranes and enzymes and cause a series of chain reactions, such as cancer induction, atherosclerosis, atherosclerosis, etc. Cell senescence and so on, it can be seen that lipid peroxide in rancid oil is very serious to human health.
3.Toxicity of rancid oil after oxidation
The oxidation of rancid oils and fats can produce toxicity and reduce their nutritional value. In the past, it was believed that the decrease of nutritional value was mainly due to the destruction of unstable vitamins by peroxides in fat. Studies have shown that rats eating rancid and oxidized fat can delay their growth, such as excessive intake, which may cause death. If fresh fat is added to excessively oxidized fat, fresh fat will play a protective role, but does not change the nutritional value of the original oxidized fat.
Oil rancidity polymerization can also produce toxicity. Thermal polymerization is different from oxidative polymerization. It does not produce unpleasant odor. It is not easy to detect their existence. Oils or fats improperly heated contain simple dimers, cyclic fatty acids, epoxides, lactones, polymers, phthalates and other toxic components.
Therefore, rancid grease is not edible. In order to avoid the oxidation and rancidity of grease, the storage time can be prolonged by sealing, avoiding light, low temperature storage and avoiding the contact of iron, copper and other utensils.