The phenolic composition and antioxidant capacity of soluble and bound extracts in selected dietary spices and medicinal herbs

Summary Phenolic compounds, commonly found in plant‐based foods, exist in free or bound form. Despite much research on the soluble phenolics in spices and herbs, their bound phenolics have not been intensively investigated. In this study, six common dietary spices and medicinal herbs (Padang cassia, oregano, clove, Chinese cassia, Japanese knotweed and peel of pomegranate) were selected to evaluate and compare their phenolic composition and antioxidant capacity in soluble extracts (SEs) and bound extracts ( BE s). Generally, the samples had high total phenolic content and antioxidant capacity, with lower levels in the BE s. From the HPLC results, (+)‐catechin, (−)‐epicatechin, eugenol, cinnamaldehyde and carvacrol were the major phenolic compounds in the SEs, and gallic acid, p ‐coumaric acid and ellagic acid in the BE s. Phenolic compounds are likely the major contributors to the antioxidant capacity of these plant samples. Overall, these dietary spices and medicinal herbs can be excellent sources of natural antioxidant phenolics.