Updated methodology to determine antioxidant capacity in plant foods, oils and beverages: Extraction, measurement and expression of results

The comparison between antioxidant capacity values reported by different laboratories is quite difficult because of substantial differences in sample preparation, extraction of antioxidants and expression of results. An updated methodology to determine of antioxidant capacity in plant foods, oils and beverages – including extraction of antioxidants, measurement of antioxidant capacity and expression of results – is presented. During sample preparation, loss of antioxidants in drying and milling steps must be minimized. Antioxidant capacity is determined in aqueous-organic extracts (combining at least two extraction cycles) and in the corresponding residues (acidic hydrolyzates to release condensed proanthocyanidins and hydrolyzable phenolics). Different aspects, such as type of solvent and possible interferences form non-antioxidant compounds, that may affect the results of the most common methods of antioxidant capacity (FRAP, ABTS, DPPH and ORAC) are discussed. The different ways of expressing antioxidant capacity results, including kinetic parameters, are described.