An oxygen scavenging system comprising a free radical scavenger (e.g., α-tocopherol, trimethylhydroquinone, ubiquinol, carotenoids, flavonoids, etc. and mixtures thereof) and a transition metal (e.g., iron (II), copper, manganese, cobalt, etc. and mixtures thereof) in a medium is generally provided. The medium containing the antioxidant and the transition metal has been thermally processed by heating to at least about 150° F. for at least about 10 minutes. Methods of removing oxygen from an environment surrounded by a medium containing the oxygen scavenging system and methods of making the oxygen scavenging system in a medium are also provided.