Spatial Distribution of Endogenous Molecules in Coffee Beans by Atmospheric Pressure Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging.

Mass spectrometry imaging (MSI) is a promising chemical imaging method. Among various endogenous molecules, mapping the concentration and the spatial distribution of specific compounds in the coffee bean tissue is of tremendous significance in its function research, as these compounds are critical to grading coffee beans at the molecular level, determining the geographical origin, and optimizing storage conditions of coffee beans. In this paper, we established an atmospheric pressure (AP) matrix-assisted laser desorption/ionization (MALDI) MSI method for the microscopic distribution analysis of endogenous molecules, for example, sucrose, caffeine, and caffeoylquinic acid, in the coffee bean endosperm. Experiments were done on the differences between coffee beans from eight countries. Principal component analysis (PCA) was performed using IMAGEREVEAL software. The results showed that the chemical composition and relative content of coffee beans from different origins are different. Our work provides a detection method that may be used for coffee bean quality identification, efficient use, product traceability, and product counterfeiting.