 Hydroxytyrosol itself in pure form is a colorless, odorless liquid.The olives, leaves and olive pulp contain large amounts of hydroxytyrosol (compared to olive oil), most of which can be recovered to produce hydroxytyrosol extracts.However, it was found that black olives, such as common canned variety, containing iron(II) gluconate contained little hydroxytyrosol, as iron salts are catalysts for its oxidation.