The recent recall of a certain brand of oils and fats that contained “excessive carcinogens” has once again become a focus of attention. So, what are the unsafe factors in cooking oil? In addition to this benzopyrene, what troubles will there be? Since many friends and the media are asking, I will personally know and answer them together. I am indeed not a food safety expert and can only answer this question with the basic knowledge of food science.

To list suspects of toxic substances in oil, it is a long string. Some of them are "toxic by nature", some are poisons caused by environmental pollution or pesticide pollution, others are harmful substances introduced during storage or processing, and even non-edible adulterants.

Natural oils in oilseeds are eaten daily by consumers, either from seeds of oil-bearing plants, or from the animal's adipose tissue (fat, plate oil) or cream (such as butter). The so-called natural poison is the natural toxin of the plant. For example, cottonseed oil contains gossypol, and rapeseed oil contains glucosinolates and erucic acid, which are harmful to the human body when consumed in large amounts. Therefore, the country will promote the cultivation of low-cotton phenolic, low erucic acid varieties.

Poisonous plants that are polluted by pesticides and polluted by the environment grow in the fields. They absorb the pollution of farmland and irrigation water, such as lead, arsenic, mercury, cadmium, etc., and also absorb difficult-to-decompose pesticide residues, such as BHC and soybeans. , rapeseed, peanut commonly used pesticides and herbicides in the cultivation process. However, because oil and fat raw materials are the seeds of plants, under the same level of pollution, the degree of contamination of seeds will be lower than that of roots, stems, and leaves. Plants also have a loving heart, and they are unwilling to leave bad things to future generations.

After oilseeds are harvested, they may also be contaminated during storage. The most common of these is due to unsatisfactory storage conditions, mildew on the seeds, and contamination of mycotoxins. The most familiar and most carcinogenic to people is aflatoxin. Rice, corn, peanuts, and all kinds of nuts are easily contaminated with Aspergillus flavus, so the oil they press must monitor the amount of aflatoxin residues. The storage and drying process after harvesting may also be contaminated with some harmful substances, such as gas or particulates emitted from asphalt on the road, car exhaust, and carcinogens generated by rubber-rubber friction, which may be attached to the seeds in small amounts; and pesticides, weeds, etc. The stacking of agents, etc. may also cause chemical contamination.

The processing of toxic oilseed oil that may be introduced during the processing of oils and fats may also cause pollution. Squeezing processing is direct physical pressing and oiling, and will not introduce solvent pollution. In comparison, the quality of produced oil is better. Especially the kind of fat with rich aroma, it is most suitable to produce by this method. For example, peanut oil and sesame oil do not require decolorization and deodorization, otherwise they lose their flavor. However, most oils undergo degumming, decolorization, deodorization, deacidification, and many other refining processes. In this process, they involve the use of kaolin, diatomaceous earth, and the like. If these substances are of poor quality, they may be introduced. Heavy metal contamination; also involves treatment with acids, bases, and organic acids, and chemical contamination may also be introduced if the quality of these processing aids is not critical.

After squeezing, it is impossible to press all the oil out. There must be a lot of grease in the oiled cake. At this point it must be extracted with a solvent. Some materials with a low percentage of oil, such as soybeans, rice bran, corn embryos, and the like, are difficult to extract by direct pressing and can only be extracted by solvents. These solvents are the most "kines" of oils and fats, such as n-hexane, butane, and No. 6 solvent oil, which can be extracted very thoroughly. These solvents are also very volatile, so long as they are heated to a lesser temperature, they evaporate away, and the condensate can also be recycled. What is left is vegetable oil that is not easily volatile. This method of producing oil is called leaching. Of course, there will be a little bit of solvent remaining, but as long as the process is in place, the quality of the solvent itself will pass, and the residual solvent in the final product will be minimal and will not be harmful to health.

The oil extracted by leaching is also refined. In this series of complex processes, some vitamin E and carotene are lost, phospholipids and phytosterols are removed, and the nutritional value of the oil is reduced. At the same time, because of the relatively high processing temperatures in some aspects, there will be a small amount of cis-trans isomerism of fatty acids, resulting in trans-fatty acids. Therefore, most refined vegetable oils, even if they are not hydrogenated, will contain a few tenths to a few percent of trans fatty acids.

Before and after processing, grease has one of the most feared things - oxidative rancidity. Oil-pressed raw materials are prone to oxidation during storage. Oxidation also occurs after long-term storage. Oxidation begins with a small amount of free radicals, and gradually “the fire of the stars can poke the original”, resulting in a large number of oxidized rancid products, the oil will produce a fresh taste, and even a clear “hakara”, which contains a large number of toxic substances. In fact, as long as there is no taste before, the increase of hydroperoxide in oils and fats will already have an effect on the aging of the human body. The quality in this regard should be judged using peroxide values. The oil has a long sales cycle. To avoid the troubles caused by oxidation, companies usually add antioxidants to the oil. The most commonly used is TBHQ, which is the kind of substance that is added to the instant noodles. The McDonald’s fried chicken pieces are exposed. That kind of substance "tertiary butyl hydroquinone", as well as BHA, BHT and so on. These are the antioxidants that the country is allowed to use. There is no need to fear because of strange chemical names.

Finally, the grease will be shipped out of the factory. At this time, be careful about the pollution that the inferior packaging material may bring, because many pollutants with benzene rings are easily soluble in grease.

The poison that is produced in the kitchen after the oil is bought home, in addition to being prone to oxidation over long periods of time, there is one of the biggest sources of danger --- that is, the harmful substances produced by cooking heat. The longer the heating time, the higher the temperature and the more harmful substances and carcinogens are produced. Heating above 300 degrees, even for a short period of time, can produce a large amount of carcinogen benzopyrene. At the temperature of daily cooking, the longer the heating time, the more benzopyrene produced in the oil. At the same time, the longer the oil is heated, the more trans-fatty acids therein, the more oxidation, polymerization, and cyclization products are produced, and these are all harmful to health.

The most frightening ones are the repeated use of cooking oil in restaurants, and the use of cooking oils that have been “over-fired”. When the fire is over, it is a fire in the pot when cooking or boiling. Some chefs do not take it for granted. They even feel that it is “cool” and very fragrant. In fact, the “smoke paste” left over from the fire has particles that are caused by overheating of fats and oils, among which carcinogenic benzene. And the content of the germanium is very high. Cooking scales are also rich in carcinogens. The fumes that the grease burns when it is heated are strong carcinogens. Whether it is fried smoke, smoked kebabs or barbecued meat, frequent exposure increases the risk of lung cancer.

Poisons from accidents and adulteration If there are abnormal accidents during food processing, it is likely to contaminate the product. Among the pollution accidents involving oils and fats, the most famous one was the Japanese rice bran oil pollution incident of 1968. It was listed as one of the “eight pollution incidents” in the world. When an edible oil factory was producing rice bran oil, polychlorinated biphenyl liquid was used as the heat transfer oil in the deodorization process. Due to poor production management, the leaking of heat-conducting oil resulted in rice bran oil being contaminated with PCBs, causing an astonishing event of more than 1600 poisonings. In 1979, similar rice bran oil pollution incidents occurred in Taiwan and more than 2,000 people were affected.

As for man-made adulteration, it should not have been a topic of discussion, but it does not exist in reality. For example, blending cooking oil with mineral oil, cooking oil (processed cooking oil), or adding Sudan, which is not a food coloring agent, is a typical “artificial doping”.