Phenolic profile and antioxidant activity of buckwheat (Fagopyrum esculentum) herb and root extracts

Abstract

Buckwheat (Fagopyrum esculentum Moench.) is a plant from Polygonaceae family, commonly used as a pseudocereal since it is nutritionally similar to grains. Due to high rutin content, it is traditionally used as a remedy for cardiovascular diseases. While numerous phenolic compounds were identified in this plant, only several have been quantified so far. The objective of this work was to obtain detailed phenolic profile of 80% ethanolic extracts of rhizoma, stems, leaves, flowers, and complete aboveground parts of buckwheat cultivated in Serbia. Total of 45 phenolics, including phenolic acids, flavonoids, coumarins and lignans, were quantified by LC-MS-MS technique. In addition, antioxidant activity was evaluated for herb and rhizoma extracts, regarding their ability to reduce Fe3+-TPTZ complex, scavenge DPPH, O2-, OH and NO radicals, and inhibit lipid peroxidation. Dominant phenols in all investigated extracts were quercetin and its glycosides - rutin, isoquercitrin, quercitrin and hyperoside, accounting for 16-18% of herb, flowers and leaves dry extract, thus making buckwheat a species extraordinarily rich in flavonols. Phenolic acids were less abundant, their total content not exceeding 4%, with quinic, 5-O-caffeoylquinic and (to a lesser extent) protocatechuic acid as the most significant. Both herb and rhizoma extracts exhibited high reduction capacity and radical-scavenging potential, in some cases higher than that of commercial antioxidants. In general, herb exhibited higher activity, which is in line with found higher phenolics content. Obtained results confirm F. esculentum to be a rich source of bioactive natural products and a valuable potential ingredient of functional foods.