Evolved gas analysis by single photon ionization–mass spectrometry: A tool to distinguish different types of coffee, and semiluxury natural foodstuff.

Introduction In this study, the applicability of thermogravimetry (TG) coupled to single photon ionization time-of-flight mass spectrometry (TG-SPI-TOFMS) for evolved gas analysis (EGA) of coffee was demonstrated. Coffee is a chemically well-known complex food product of large scientific and commercial interest. Methods A simultaneous thermogravimetry/differential scanning calorimetry device (STA) was coupled to single photon ionization time of flight mass spectrometry (SPI-TOFMS) for evolved gas analysis (EGA). Thermal resolution with thermogravimetric signal (TG) is delivered by STA. On-line coupled EGA with SPI-TOFMS retains the thermal information for a chosen heating program from the STA and substantiates these with correlating mass spectra. The application of vacuum ultraviolet (VUV)-photons (8-12 eV) for soft ionization, allows almost fragment-free ionization. Thus, it becomes possible to interpret mass spectra of complex matrices, like natural products evolving simultaneously several molecules, without an additional separation step. The TG-SPI-TOFMS on-line coupling offers the possibility to track subset mass traces during one STA run. Focusing on material depended mass traces, differentiation of organic matrices is obvious[1]. Results The roasting process and roasting experiments can be done laboratory-based on the micro scale using single beans in TG-SPI-TOFMS experiments. The gases evolved during the simulated roasting process can be analyzed by comparing the gained mass information with the literature. As known, Arabica as Robusta contains the diterpene Cafestol, but only the Arabica coffee bean contains Kahweol. The masses of those dehydrated diterpenes (m/z 296 and m/z 298) can be tracked by EGA during one cycle. The figure shows the results of the simulated roasting process of a single Arabica coffee bean (left column) and an individual Robusta (right column) coffee bean.  The mass spectra B and D after 20 minutes allow discrimination between Arabica and Robusta coffee. The mass spectra at 245 °C (A, C) reveal different composition ratios. Further experiments revealed the possibility of detecting Kahweol as a characteristic of the Arabica coffee also in powders and blends (roasted and grinded). Conclusions The application of TG coupled to Single Photon Ionization - Time-of-Flight Mass Spectrometry for simulated coffee roasting experiments (individual coffee beans) and grinded coffee powders, gave promising results and valuable insights in the chemical composition of the evolved roasting gases. Novel Aspect TG-SPI-TOFMS was applied to simulate the roasting process of single green coffee beans in the laboratory. Almost fragment-free ionization allows the interpretation of evolved gases’ chemical composition