Used cooking oil for frying repeatedly can be hazardous to health because the oil constituent compounds can undergo physical changes and chemical changes.
Repeated use of cooking oil usually found in stalls or places that sell other fried foods.
Cooking oil that has not been used is composed of unsaturated fatty acids or fatty acids containing double bonds. The degree of oil unsaturation decreases with increasing temperature even heating can lead to fatty acid chains broken into free radicals that are harmful to health.
Based on research conducted at the oil heating for 30 minutes at temperatures above 125 degrees Celsius could lead to the emergence of novel compounds that are toxic to the body from breaking the chains of fatty acids. One of the compounds that are toxic trans 2-hydroxyl oktenal (HNE). This compound is very dangerous because it is easily absorbed by the body and toxins bersifar (toksit) of biomolecules in the body such as DNA and proteins. besides continuous heating oil terhadapat can produce also some other compounds that are toksit of the body that is 4-hifroksihekseksal, 4-hidroksioktenal and hepta 2,4-dienal.
Therefore, the use of cooking oil should be considered so as not to be used repeatedly. For stalls or places where fried foods should be noted that the use of oil once or twice used had expired so it can be added again in the new oil, not one liter of oil used once.
Although harmful to health, cooking oil can be used to make biodiesel fuel by transesterification reaction, even based on research conducted several parties biodiesel cooking oil is more environmentally friendly than diesel.