Methodological Considerations for Characterizing Potential Antioxidant Actions of Bioactive Components in Plant Foods

The study of free radicals and antioxidants in biology is producing medical revolution that promises a new age of health and disease management. From prevention of the oxidative reactions in foods, pharmaceuticals and cosmetics to the role of reactive oxygen species (ROS) in chronic degenerative diseases including cancer, autoimmune, inflammatory, cardiovascular and neurodegenerative (e.g. Alzheimer's disease, Parkinson's disease, multiple sclerosis, Downs syndrome) and aging challenges continue to emerge from difficulties associated with methods used in evaluating antioxidant actions in vivo. Our interest presently is focused on development of neurodegeneration models based on the integrity of neuronal cells in the central nervous system and how they are protected by antioxidants when challenged by neurotoxins as well as Fenton chemistry models based on the profile of polyunsaturated fatty acids (PUFAs) for the assessment of antioxidant actions in vivo. Use continues to be made of several in vitro analytical tools to characterise the antioxidant propensity of bioactive compounds in plant foods and supplements. For example, the oxygen radical absorbance capacity (ORAC), ferric reducing antioxidant power (FRAP), total oxidant scavenging capacity (TOSC), the deoxyribose assay, assays involving oxidative DNA damage, assays involving reactive nitrogen intermediates (e.g. ONOO(-)), Trolox equivalent antioxidant capacity (TEAC) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. There is need to agree governance on in vitro antioxidant methods based on an understanding of the mechanisms involved. Because some of the assays are done in non-physiological pH values, it is impossible to extrapolate the results to physiological environment. The consensus of opinion is that a mix of these tools should be used in assessing the antioxidant activities in vitro. The proof of bio-efficacy must emanate from application of reliable in vivo models where markers of baseline oxidative damage are examined from the standpoint of how they are affected by changes in diet or by antioxidant supplements.