2021 年 69 巻 2 号 p. 34-38
The leaves of evergreen hardwoods such as tea tree (Camellia sinensis) are covered with thick wax, and overcoming this is a challenge in mass spectrometry imaging (MSI) of tea leaves. MSI experiments for secondary metabolites in tea leaves were conducted by matrix-assisted laser desorption/ionization (MALDI) using a liquid matrix and by DIUTHAME (desorption ionization using through hole alumina membrane). The liquid matrix was applied by a manual operation using a pipette tip as a spatula. Despite this easy preparation for MALDI imaging, mass images that reflect the shapes and tissue structures of the tea leaves were acquired for m/z 175 presumably derived from theanine. In DIUTHAME imaging of tea leaf transverse sections, mass images were acquired for m/z 217 and m/z 291 presumably derived from caffeine and epicatechin, respectively, in addition to that for m/z 175. In particular, for theanine, which is a palatable taste (umami) component of green tea, visualization of the spatial distribution by MSI of tea leaves has not been reported so far. In the present study, the potential of MSI to analyze theanine translocation dynamics in tea leaves was demonstrated for the first time by MALDI imaging with liquid matrix and DIUTHAME imaging.