Why does cooking oil smell bad?

The culprits cause metabolic cooking oil to be everywhere in the kitchen, including light, heat, water, bacteria and air.

According to Susan Richardson, a professor of chemistry at the University of South Carolina, USA, any edible oil product contains unsaturated fats or polyunsaturated fats, which allow fat to survive in the liquid form. Room temperature, can become rancid.

Unsaturated fats contain double carbon bonds in the structure, but these bonds can be broken down by oxygen in the air. That is oxidation, according to Richardson. If the user forgets to close the bottle of cooking oil such as vegetable oil, sesame oil or olive oil, the cooking oil inside will be exposed to oxygen.

" Oxygen molecules will squeeze in between and break down the double carbon bond, forming carbon-oxygen bonds, " Live Science quoted John Malin, associate professor of chemistry at Missouri University, USA. The new link leads to the formation of several compounds such as aldehyde, ketone or carboxylic acid, causing a rancid odor.

Edible oil smells and smells due to many different causes.(Photo: Serghei Starus).

Water has the same effect , because the H ₂ O molecule contains an oxygen atom. When water falls into cooking oil, part of the H ₂ O molecule enters the double carbon bond during hydration . The rate of oxidation and hydration is accelerated if there is light. Ultraviolet light is more powerful than visible light because it carries more energy. "That's why we need to preserve cooking oil in a shady place and close the lid , " Malin said.

Temperatures also promote chemical processes, and can make oils eat faster. When heated, the molecules move around, fluctuate rapidly and bump into each other. However, Malin recommends against cooking oil in the refrigerator. Cold temperatures slow down the motion of molecules in liquids. As they move more slowly, some molecules separate from the solution and stratify, leading to lumpiness. The consumption of cooking oil in this condition does not affect health, but most people prefer transparent cooking oil, according to Malin.

Some bacteria are also agents that cause cooking oil to smell. Edible oil contains triglycerides, a chemical compound consisting of one molecule of glycerol and three fatty acids. Some bacteria separate fatty acids from triglycerides. Fatty acids are separated causing odors in cooking oil.

Experts insist not to use rancid cooking oil. "The rancid food not only loses vitamins but is also capable of developing toxic compounds , " said Eric Decker, head of the Food Science Department at the University of Massachusetts Amherst, USA. These toxic compounds are associated with premature aging, neurological disorders, cardiovascular disease and cancer.