Assessing the Spatial Distribution of Key Flavonoids in Mentha × piperita Leaves: An Application of Desorption Electrospray Ionization Mass Spectrometry Imaging (DESI-MSI)

Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) was used to assess the spatial distribution of some key flavonoids in peppermint (Mentha × piperita L.) leaves.The chemical images were generated by applying DESI-MSI on the peppermint leaves imprinting while acquiring the spectra in the negative ion mode.The following key flavonoids were detected and grouped within well-known biosynthetic routes in plants: naringenin route [naringenin, sakuranetin, hesperetin, hesperidin, luteolin, and apigenin]; luteolin route [luteolin, chrysoeriol, luteolin-7-O-D-glucuronide, luteolin-7-O-D-glucoside, luteolin-7-O-neohesperidoside]; apigenin route [apigenin, apigenin-7-O-gentiobioside, apigenin-7-O-neohesperidoside, thymusin/pilosin, pebrellin, acacetin/genkwanin, ladanein, xanthomicrol/pedunculin/nevadensin].Maps of the spatial distribution of these flavonoids throughout the peppermint leaves within each route were then displayed.The results described herein comprise an important (although still underexplored