Abstract

Antioxidants are groups of substances able to prevent and delay the oxidation of easily oxidizable molecules and avoid free radicals’ formation. In living organisms, the main free radicals are reactive oxygen species and reactive nitrogen species. At low levels, they are involved in the regulation of diverse physiological processes, but an imbalance between free radicals and the ability of the body to eliminate them results in a pathological condition called oxidative/nitrosative stress. Oxidative/nitrosative stress causes damage to cellular structures such as lipids, nucleic acid, and proteins, compromising cellular health and viability and inducing the development of several diseases. Physiological systems are able to contrast the free radical excess, through the endogenous enzymatic materials (e.g., uric acid, glutathione etc.), and via transcription factor activation. The uptake of natural antioxidants can contribute to prevent cellular damage and exert beneficial effects. Natural antioxidants are generally derived from plant sources and they play an important role by directly scavenging free radicals or increasing antioxidant defences. Natural antioxidants have gained remarkable interest and several methods have been developed for identifying their antioxidant capacity. This chapter reviews the major in vitro and in vivo assay procedures for the antioxidant activity estimation describing materials, extract types, extracts/pure compounds' concentrations, step by step processes and calculations for each assay. Advantages and limitations, as well as the molecular mechanisms of each method have been reported.