A. Oleate B. Linoleate C. Linolenate III. FATTY ACID OXIDATION BY SINGLET OXYGEN IV. OXIDATION OF MIXTURES OF FATTY ACIDS AND VEGETABLE OILS V. DECOMPOSITION OF HYDROPEROXIDES VI. FLAVOR REVERSION A. Causes of flavor reversion I. Linolenic acid 2. Phosphatides 3. Nonglyceride components B. Control measures 1. Metal inactivators 2. Processing with minimum exposure to oxidation 3. Hydrogenation VII. CONCLUSIONS VIII. REFERENCES

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The activity of antioxidants in foods and biological systems is dependent on a multitude of factors, including the colloidal properties of the substrates, the conditions and stages of oxidation and the localisation of antioxidants in different phases. When testing natural antioxidants in vitro, it is therefore important to consider the system composition, the type of oxidisable substrate, the mode of accelerating oxidation, the methods to assess oxidation and how to quantify antioxidant activity. Antioxidant effectiveness is also determined by the heterogeneity and heterophasic nature of the system, 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 cannot be a short-cut approach to determining antioxidant activity. Each evaluation should be carried out under various conditions of oxidation, using several methods to measure different products of oxidation. Because most natural antioxidants and phytochemicals are multifunctional, a reliable antioxidant protocol requires the measurement of more than one property relevant to either foods or biological systems. Several recent studies on natural phytochemical compounds produced con¯icting results because non-speci®c one-dimensional methods were used to evaluate antioxidant activity. There is a great need to standardise antioxidant testing to minimise the present chaos in the methodologies used to evaluate antioxidants. Several methods that are more speci®c should be used to obtain chemical information that can be related directly to oxidative deterioration of food and biological systems.

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