Revealing the spatial distribution of chlorogenic acids and sucrose across coffee bean endosperm by desorption electrospray ionization-mass spectrometry imaging

Endosperm tissue of cross-sectioned green arabica coffee beans was analyzed by the ambient ionization technique desorption electrospray ionization-mass spectrometry (DESI-MS) imaging and the spatial distribution of chlorogenic acids and sucrose across the bean endosperm was revealed. Quinic acid and feruloylquinic acid were located, preferably, in the hard external region of the endosperm, while caffeoylquinic acid was detected in high levels in the soft internal region. This non-homogeneous spatial distribution appears to be related to different functions of these distinct tissue regions. Sucrose was detected across the whole coffee bean endosperm. A damaged green coffee bean with holes caused by the coffee berry borer (Hypothenemus hampei) was also analyzed and increased levels of caffeoyl-sinapoylquinic acid and the unidentified m/z ion 535 were observed in the injured endosperm region compared to other regions. This new approach, of using DESI-MS imaging for coffee analysis, could help expand our knowledge about coffee chemistry and physiology.