ABSTRACT
According to a widely used definition, an antioxidant is any substance that, when present at lower concentrations than those of an oxidizable substrate (such as lipids, proteins, deoxyribonucleic acid [DNA] or carbohydrates), significantly delays or prevents oxidation of that substrate [1, 2]. Neither this definition nor other definitions [3] restrict antioxidant activity to a specific group of compounds or to any particular mechanism of action. Natural antioxidants play a decisive role in different systems: i) in plants, they act as protecting agents against radiation or microbial infections, ii) in
foods, they delay or inhibit the formation of toxic lipid oxidation products, maintaining nutritional quality and increasing shelf life, and iii) in biological systems, along with endogenous defenses (enzymes, vitamins, proteins, and others), dietary antioxidants may help prevent or slow the oxidative stress induced by free radicals [4]. Since considerable evidence indicates that oxidativedamage may contribute to the developmentof age-related and degenerative diseases, the protective effects of beneficial compounds have been ascribed to their antioxidant activity, although many antioxidants in vivo probably act by other mechanisms than in vitro assays or are unlikely to have such effects at the concentrations available in plasma [5, 6].
