 Most food compounds listed as antioxidants – such as polyphenols common in colorful, edible plants – have antioxidant activity only in vitro, as their fate in vivo is to be rapidly metabolized and excreted, and the in vivo properties of their metabolites remain poorly understood.For antioxidants added to food to preserve them, see butylated hydroxyanisole and butylated hydroxytoluene.In the following discussion, the term "antioxidant" refers mainly to non-nutrient compounds in foods, such as polyphenols, which have "antioxidant capacity" in vitro and so provide an artificial index of antioxidant strength – the ORAC measurement.