A first class of antioxidant species are those which effectively contribute to lower transition metal activity. These act generally by chelation and the better known are citric acid, phosphoric acid and some of its derivatives. These substances act not as antioxidants per se but rather as synergiistic ingredients which effectively diminish the rythm of chain initiation.

Antioxidants which act by interrupting a radical chain once started may be water soluble, such as ascorbate (Vitamin C) and its stereoisomer erithorbate, or oil soluble, such as the tocols (tocopherols and tocotrienols, of which a-tocopherol is Vitamin E)), the flavanones and flavonols present in vegetables and herbs and very abundant in tea, and the synthetic antioxidants BHT, BHA, TBHQ, or ethoxyquin, and other polyphenols such as gallic acid derivatives which occur in nature.

The latter category are also known as phenolic antioxidants, and their antioxidative capability seems to bear a relationchip not only to the number of phenol groups occupying 1,2 or 1,4 positions in an aromatic ring, but also to the volume and electronic characteristics of the ring substituents present Antioxidant activity may also be shown by quinonoidal systems as that present in phytomenadione (Vitamin K).

Antioxidant effectivity may be measured as the ratio of the induction period under a certain set of experimental circumstances (say 100 ºC, p(O₂)=1 atm), for a given concentration, normally expressed as ppm (w/w), in a specified oil or fat.

If the protection factor for an antioxidant is Af , it may therefore be calculated as the ratio of induction period If when antioxidant is present and Io when it is absent.

Varying antioxidant concentration or mixing different antioxidants in different proportions may be performed to obtain data on synergies, antagonisms and optima.