Comparative metabolomics reveals differences in flavonoid metabolites among different coloured buckwheat flowers

Flavonoids are the largest group of secondary metabolites, and they play important biological functions. Buckwheat, particularly its flowers, contains a considerable amount of flavonoids. However, only a few flavonoid metabolites have been identified to date, and differences in flavonoid metabolites between Tartary and common buckwheat flowers have not yet been reported. In the present study, one Tartary buckwheat variety with green flowers and three common buckwheat varieties with white, pink and red flowers were sampled. Flowers of red-flowered common buckwheat had the highest total flavonoid content, followed by Tartary buckwheat flowers. The flower extracts were analysed using ultra-performance liquid chromatography-electrospray ionisation-tandem mass spectrometry (UPLC-ESI-MS/MS), and a total of 188 flavonoid metabolites, including 53 flavones, 39 flavonols, 33 flavone C-glycosides, 24 flavanones, 18 anthocyanins, 11 isoflavones, 5 proanthocyanidins and 5 flavonolignans, were detected. Multivariate statistics revealed a distinct difference in the flavonoid metabolism between Tartary and common buckwheat flowers, and both of them had unique functional metabolites. For example, common buckwheat flowers were rich in luteolin and apigenin, whereas Tartary buckwheat flowers were rich in tricin. These results provide new information regarding the flavonoid metabolites of buckwheat flowers and offer important theoretical support for the exploitation of buckwheat flowers.