Toxicity of reused cooking oil: A review

Repeated heated cooking oil has been a regular practice to save cost and people believe that vegetable oil was the best choice of cooking oil since it has functional and nutritional benefits to consumers such as high vitamin and antioxidant content. However, the consumption of reused vegetable oil could give harmful effect on body cells. Repeatedly heated vegetable oil can produce other harmful compounds or byproducts with the potential risk to human body systems, such as volatile compound (alcohol, aldehyde, and ketone), polar compound (monoacylglyceride, diacylglyceride, and glycerol), non-polar compound (trans-fatty acids) and toxic compound (acrylamide). These molecules were resulted from several reaction processes from heating including the process of hydrolysis, oxidation (oxidative decomposition, oxidative haemolytic cleavage, and millard reaction), cyclisation, isomerisation and polymerisation of oil. Formation of free radicals can cause oxidative stress and accelerate degradation of lipid. In addition, high temperature to the cooking oil could alter the antioxidant molecule function. Plus, fried food from reused cooking oil is able to change the nutritional content in food itself; for example, vitamins (E, A, B and C) and mineral component. This activity can lead to increase blood pressure, total cholesterol low-density lipoprotein (LDL), saturated fatty acid and eventually cause atherosclerosis, hypertension, neurodegenerative and even cancer. This review studies the adverse effect of repeated heated vegetable oil intake towards human and aims at increasing the awareness of the community around the world.