Synthetic antioxidants are chemicals that are synthesized in the laboratory and used as a substitute for natural antioxidants.
They delay the onset of oxidant or slow down the rate of oxidation of foodstuff.
They are added as additives to increase the shelf life of packed foods.
Common structural units found in synthetic antioxidants are phenolic -OH group and tertiary butyl group. e.g. BHT, which is 3,5-di-tert-butyl-4- hydroxytoluene.