Display omitted •Folin-Ciocalteu reagent and AlCl3 are used to assess the total phenolics and total flavonoids.•ABTS, CUPRAC, ORAC, DPPH and many other assays are used to assess the antioxidant activity.•Colorimetric methods present many pitfalls but can be used as screening tools.•LC–MS is recommended to quantify antioxidant compounds in food matrices.•In vivo tests and clinical studies are required to attest functionality of foods. As many studies are exploring the association between ingestion of bioactive compounds and decreased risk of non-communicable diseases, the scientific community continues to show considerable interest in these compounds. In addition, as many non-nutrients with putative health benefits are reducing agents, hydrogen donors, singlet oxygen quenchers or metal chelators, measurement of antioxidant activity using in vitro assays has become very popular over recent decades. Measuring concentrations of total phenolics, flavonoids, and other compound (sub)classes using UV/Vis spectrophotometry offers a rapid chemical index, but chromatographic techniques are necessary to establish structure-activity. For bioactive purposes, in vivo models are required or, at the very least, methods that employ distinct mechanisms of action (i.e., single electron transfer, transition metal chelating ability, and hydrogen atom transfer). In this regard, better understanding and application of in vitro screening methods should help design of future research studies on ‘bioactive compounds’.