The problems of using one-dimensional methods to evaluate multifunctional food and biological antioxidants

The activity of antioxidants in foods and biological systems is dependent o n a multitude of factors, including the colloidal properties of the substra tes, the conditions and stages of oxidation and the localisation of antioxi dants in different phases. When testing natural antioxidants in vitro, it i s therefore important to consider the system composition, the type of oxidi sable substrate, the mode of accelerating oxidation, the methods to assess oxidation and how to quantify antioxidant activity. Antioxidant effectivene ss is also determined by the heterogeneity and heterophasic nature of the s ystem, the type of lipid substrate, including its physicochemical state and degree of unsaturation, the types of initiators, notably transition metals , other components and their possible interaction. For this reason there ca nnot be a short-cut approach to determining antioxidant activity. Each eval uation should be carried out under various conditions of oxidation, using s everal methods to measure different products of oxidation. Because most nat ural antioxidants and phytochemicals are multifunctional, a reliable antiox idant protocol requires the measurement of more than one property relevant to either foods or biological systems. Several recent studies on natural ph ytochemical compounds produced conflicting results because non-specific one -dimensional methods were used to evaluate antioxidant activity. There is a great need to standardise antioxidant testing to minimise the present chao s in the methodologies used to evaluate antioxidants. Several methods that are more specific should be used to obtain chemical information that can be related directly to oxidative deterioration of food and biological systems . (C) 2000 Society of Chemical Industry.