[Source: Weinan Popular Science] Cooking oil that has been heated repeatedly is what people often refer to as "old oil", such as oil for fried dough sticks and French fries. If it is not replaced in time, it will become old oil with the color of soy sauce. Old oil is not suitable

[Source: Weinan Popular Science]

Cooking oil that has been heated repeatedly is what people often refer to as "old oil", such as oil for fried dough sticks and French fries. If it is not replaced in time, it will become old oil with the color of soy sauce. Oil. Old oil is not suitable for consumption because during repeated heating, edible oil undergoes a series of chemical changes and produces many compounds that are detrimental to human health.

When frying food, the temperature of edible oil can reach 180°C ~ 200°C. At this high temperature, the edible oil will "deteriorate":

First, oxidation reaction will occur. Edible oil produces many volatile substances, including saturated and unsaturated aldehydes and ketones, polycyclic aromatic hydrocarbons, etc. Many of them are volatile toxic substances, especially acrolein, which is present in oil smoke and is a cause of lung cancer. One of the things.

The second is the hydrolysis reaction of to . Fried food releases moisture at high temperatures, which causes the edible oil to hydrolyze and produce fatty acids, causing the edible oil to quickly become rancid.

The third is the isomerization reaction. At high temperatures, cis fatty acids in edible oils are isomerized into trans fatty acids . Trans fatty acids entering the human body can cause obesity, heart disease, diabetes , Alzheimer's disease and many other health problems.

Because of this, old oil that has been heated repeatedly should not be reused, let alone edible.

Source: Citizen Science Literacy Reader Series, Shandong Association for Science and Technology

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