Metabolomics approach reveals discriminatory metabolites associating with the blue pigments from Vaccinium bracteatum thunb. Leaves at different growth stages

Vaccinium bracteatum Thunb. leaf is a valuable source of natural pigment to dye food, hair, and clothing for a thousand of years in China. However, the seasonal differences of blue hue of pigments have not been fully demonstrated. In this research, V. bracteatum Thunb. leaves were collected from eight months for metabolite analysis. The global metabolic profile in leaves was examined to distinguish the differential metabolites and monitor the dynamic changes. This research revealed that several discriminatory secondary metabolites were monotropein derivatives, flavonoid glycosides and chlorogenic acid isomers by LCMS-untargeted approach. The changes of monotropein derivatives and dimers occurred in a season-dependent manner which almost showed higher abundances in spring. Meanwhile, several free amino acids changed dramatically by HPLC-targeted measurement. Particularly, Ala, Glu, and Asp caused a positive impact on blue color. Ser, Arg, and His were negatively correlated with the color. This research provided the first evidence that the seasonal differences of blue pigment are ascribed to the systemic changes of monotropein derivatives and free amino acids in V. bracteatum Thunb. leaves.