The human body uses an antioxidant defense system to neutralize the excessive levels of reactive oxygen species. This system consists of enzymatic and non enzymatic antioxidants,catalase, peroxidase, superoxide dismutase and gluatathion s-transferease as major defense enzymes. However, ascorbic acid, tocopherol, and phenolic compounds are considered as examples for non-enzymatic antioxidants. Increasing research on natural antioxidants in foods and development of new assays has prompted critical reflection on the field. It has been common practice to identify health benefits from antioxidant activity on the cellular level with antioxidant capacity of food measured in vitro. The use of antioxidants and their positive effects on food quality has been demonstrated in a large variety of foods and beverages using various methods for detection of lipid and protein oxidation or various assays based on electron transfer or hydrogen-atom transfer. There is a need for screening studies in order to identify the mode of action of different antioxidant compounds (enzymatic and non-enzymatic in addition, comparing between synthetic and natural antioxidant compounds) by different assays, in addition to highlighting the advantage and disadvantage of it. Some of these assays depend on hydrogen atom transfer methods or electron transfer methods in addition, metal chelating compounds and free radical scavenging activity.
Key words: Synthetic and natural antioxidant compounds, assays, mechanism.
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