Visualizing the distribution of curcumin in the root of Curcuma longa via VUV-postionization mass spectrometric imaging.

Curcumin is a dietary spice and coloring agent widely used in food and herbal medicine. Herein, we visualized the distribution of curcumin in fresh Curcuma longa (turmeric) root sections using the state-of-the-art vacuum-ultraviolet (VUV, 118 nm) single photon-postionization mass spectrometric imaging method. Compared with other mass spectrometric imaging methods, the proposed method does not require any sample pre-treatment. The proposed approach could be more conducive to in situ detection of small molecules. The mass spectroscopic imaging (MSI) images of curcumin sections with a lateral resolution of 100 μm indicated that the concentrations of curcumin decreased from the phloem to the xylem of the root. We also show MS imaging of curcumin in the turmeric root at different maturity periods, revealing the transformation of this endogenous species. The result of quantitative analysis indicates that the total curcumin content of the mature turmeric root is estimated to be 3.43%, which is consistent with the previous report that the content of curcumin in the turmeric root is estimated between 3% and 5%. The report indicated that the proposed method of VUV single photon postionization MSI can be used to explore the metabolic process of plants, which is critical for herbal farming, harvest, and its ingredient extraction.