Antioxidants are added to foods and other products to prevent
rancidity. Although the exact mechanism(s) is (are) not clear,
antioxidants react with free radicals and peroxides, slowing the
development of rancidity. Certain other additives greatly enhance
the effectiveness of antioxidants. Metal scavenger and chelating
agents, such as citric acid and citrates, tie up the trace metals and
greatly reduce their catalytic activity. Synergism between
antioxidants also has been noted, and many commercial antioxidant
mixes are formulated to contain mixtures of antioxidants. The
most common of these mixtures contain both butyl-hydroxyanisole
(BHA) and butyl-hydroxytoluene (BHT).