Garlic is not reliable for detecting gutter oil

gossip:

The easiest way to detect whether it is gutter oil is: put a peeled garlic when cooking, as garlic is the most sensitive to aflatoxin. If the garlic turns red, it means that gutter oil was used, which contains a large amount of aflatoxin. If the cooking oil is good, the garlic will be white. Put the oil in your home in the refrigerator for 2 hours. If white foam appears, it is gutter oil.

the truth:

The detection of waste cooking oil has always attracted much attention. Although the health departments have stated that there is currently no universal detection method, techniques claiming to be able to identify waste cooking oil have sprung up like mushrooms after a rain. Faced with a problem that even professional organizations cannot solve, are these tips really reliable?

Difficulty in detecting waste cooking oil

What we call gutter oil nowadays actually refers not only to the oil salvaged from the sewer in the literal sense, but is a general term for discarded edible oil, including gutter oil, sewage/swill oil, old frying oil, inferior animal oil, etc.

Although quality supervision departments and scientific research institutions have been committed to finding the common points of various types of waste edible oils and fats, due to the different sources of waste edible oils and fats and the various processing and blending they have undergone, the substances they contain are diverse and the contents are also different. Previously, the five most likely successful testing methods collected by the Ministry of Health also failed in the face of refined gutter oil, so they had to continue collecting methods. It can be seen that it is extremely difficult to find a universal and reliable method.

In this case, can the rumored method really work?

Garlic testing for aflatoxin is unreliable, untrustworthy, and uncommon

Aflatoxin comes from Aspergillus flavus, is a strong carcinogen, and is also one of the harmful substances that may exist in waste cooking oil. This mold can grow on many crops, peanuts being one of them. If the production unit does not store them properly, aflatoxin can easily grow. Therefore, aflatoxin content has always been a key testing indicator for edible vegetable oils. Not only do oil refineries need to provide product inspection reports when applying for QS certification, but quality supervision and industrial and commercial departments at different levels also conduct regular inspections. For example, in the national random inspection in 2010, 14 batches of products from Guangdong were put on the blacklist, including some that exceeded the aflatoxin standard.

Although the threat of aflatoxin is long-standing, using garlic to detect aflatoxin is a new thing. We could not find any literature reports on the discoloration of garlic caused by aflatoxin in the database. If you search for related claims online, the search results all point to this rumor. Moreover, the description of the rumor is ambiguous. There is no clear statement on how much aflatoxin can be detected and how long it takes to heat before the color turns red. This greatly undermines the credibility of this method.

More importantly, the aflatoxin content in waste cooking oil does not necessarily exceed the standard. For example, although waste cooking oil reprocessed from old frying oil may contain a large amount of polycyclic aromatic hydrocarbons and trans fatty acids that are harmful to humans, it is entirely possible that the aflatoxin content is qualified. Even if garlic will really change color when it encounters aflatoxin, it does not have the ability to identify other types of waste cooking oil.

In summary, this is an unreliable, untrustworthy, and ununiversal method. Even if the garlic does not change color, it does not mean that the oil is safe.

It is not reliable to identify the authenticity of refrigerators

Regarding the method of identifying gutter oil by its solidification point, Guokr has previously published an analysis article - "Is it reliable to identify gutter oil by its solidification point?" The method mentioned in this rumor is actually just a variant.

Some cooking oils with high saturated fatty acid content will gradually solidify and precipitate solids when the temperature drops to a certain level, but the appearance should not be foam as rumored. Because waste cooking oil has been used for a long time, its composition is complex and it may be mixed with impurities such as food residues. Although larger impurities can be removed through simple filtration and it is clear at room temperature, impurities such as animal fats and proteins will gradually solidify and precipitate as the temperature drops, and may form a foamy layer on the surface of the oil.

But the same problem is that not all gutter oils will produce foam after being refrigerated in the refrigerator. Such testing is powerless in most cases, especially for refined and blended gutter oils.

There are not many ways to prevent waste oil

For edible oil of qualified quality, the garlic will not turn red or foam will appear when refrigerated. This phenomenon may be caused by gutter oil or the quality of the edible oil is not up to standard. For example, the generation of foam may be due to the fact that the impurity removal process after oil pressing is not done well. For national quality inspection departments, it is necessary to clearly distinguish between the two in order to facilitate reasonable punishment and rectification.

For consumers, any product with substandard quality is unacceptable. In this sense, whenever you encounter abnormal phenomena, you need to doubt whether the oil can be used. But consumers should also be aware that there is currently no good technical way to prevent gutter oil, and more attention should be paid to the circulation process (of course, quality and safety process supervision by relevant departments is of paramount importance).

These problematic gutter oils are mainly sold to the catering market, and supermarket retail is not the main channel. Some small restaurants and food workshops are under pressure from operating costs and have weak legal and food safety awareness, so cheap refined gutter oil is quite attractive to them. Therefore, in order to reduce the risk of encountering gutter oil, consumers need to pay attention to choosing reputable restaurants when dining out and choosing reputable brands for daily cooking oil.

in conclusion:

There is no research or theory to support that aflatoxin can be detected in garlic. Freezing is effective for a small portion of waste cooking oil, but it is not a universal method and is not applicable universally. There is currently no universal method for detecting gutter oil. To prevent gutter oil, consumers need to try to choose reputable restaurants and cooking oil.

About waste cooking oil:

Crude gutter oil is dark in color and has a bad odor, and can be easily discovered if it is disguised as edible oil. If unscrupulous merchants use technical means to remove impurities from waste oil, such as adsorption and decolorization, vacuum deodorization or adding flavors, the refined waste oil will be difficult to identify with the naked eye. If it is carefully blended with qualified edible oil, it is possible to meet the national standards in terms of quality indicators such as color, clarity and refractive index, and even various testing indicators can meet the national standards for edible oil hygiene (GB

2716-2005) is not impossible, after all, these test indicators are formulated for normal production processes.

Because such processing is not technically complicated and the cost is not too high, it is still profitable for businessmen. But what you get is just oil that looks like cooking oil, not real cooking oil that you can eat.

If we really want to refine waste cooking oil to the point where it is safe for consumption, we must not only thoroughly remove various toxic and harmful impurities such as aflatoxin, heavy metal elements, benzopyrene, polycyclic aromatic hydrocarbons, detergents, etc., but also be careful not to introduce new harmful substances during the processing process, and at the same time, the equipment must also be kept clean and hygienic. With all this effort, the technical difficulty and cost will naturally be high, and there may be no profit at all.