The past tense of Oxidize is oxidized.
verb. ['ˈɑːksəˌdaɪz'] add oxygen to or combine with oxygen.
1. Verb, base form Enzymes in the liver work to oxidize it into a substance that can be used for energy.
verb. ['ˈɑːksəˌdaɪz'] enter into a combination with oxygen or become converted into an oxide.