46 May / June 2017 Screening Results and Discussion


Figure 8 shows the GC-MS total ion chromatograms (TICs) for three organically cultivated, fermented, dried cocoa beans from different geographical sources. Characteristic compounds in the headspace eluted in less than 90 seconds under the GC-MS conditions listed in Table 1. Peaks marked with an asterix (*) represent candidate VOC and SVOC markers previously mentioned, which potentially can be used to evaluate the acceptability


and confirmation of the authenticity of a raw material shipment [2]. By comparing the chromatographic fingerprints of VOC/ SVOC compounds generated by the sample to a representative or reference VOC/SVOC profile from an acceptable lot, the analyst can then make a very rapid assessment of the quality of that cocoa bean/chocolate product or commodity. Additionally, the mass spectral data of these eluted peaks could be further examined for clarity and confirmation and compared with reference data bases if required.


Table 1: The chromatographic separation conditions for cocoa powder samples


Gas Chromatographic Separation Conditions Sample delivery SPME phase


Injector temperature


Transfer line temperature Injector split ratio


Column Technology (Restek® State College, PA)


,


Initial Temperature/ Hold Time Final Temperature/Hold Time Temperature Ramp Rate


Table 2: Mass Spectrometer Parameters


Mass Spectrometer Operating Conditions Mass spectrometer Ionisation source


MS Operating temperature Mass range Resolution


MS scan rate Detector


Toroidal Ion Trap Electron ionisation 200°C


41-500 amu


< 0.5 m/z at 300 amu 10-15 Scans/s


Electron Multiplier SPME (solid phase micro-extraction)


Divinylbenzene/Polydimethylsiloxane (DVB/PDMS, 65 µm)


270°C 250°C 10:1


MTX®


-5: low-polarity phase diphenyl dimethyl polysiloxane; 5 m x 0.1 mm x 0.4 µm


50°C for 10 s 280°C for 50 s 2°C/s


Conclusion


This study has shown that VOCs and SVOCs from cocoa beans can be rapidly screened at the source using headspace SPME sampling coupled with a novel portable GC system fitted with a toroidal trap mass spectrometer. Using this combination, both field and laboratory screening of marker compounds can indicate initial raw material quality and support rapid decision making. The ability to analyse a wide variety of organic compounds in cocoa and other natural food products provides timely and important information at the commodity source. In addition, the short analysis time allows the user to quickly analyse multiple samples on- site if required and allow non-experienced personnel to make critical decisions without have to send the samples back to the lab for further clarification. However, it should be emphasised that this has been a preliminary investigation and although very promising, additional works needs to be carried out to characterise and identify a more comprehensive suite of contaminants.


References


1. Identification of the Key Aroma Compounds in Cocoa Powder Based on Molecular Sensory Correlations; F. Frauendorfer, P. Schieberle, Journal of Agriculture and Food Chemistry, 54, 15, 5521–5529, 2006.


2. Development of a GCxGC-TOFMS Method using SPME to Determine Volatile Compounds in Cacao Beans; E.M. Humston et. al., Journal of Separation Science, 32, 2289 – 2295, 2009.


3. Hand-Portable Gas Chromatograph- Toroidal Ion Trap Mass Spectrometer (GC-TMS) for Detection of Hazardous Compounds; J. Contreras, J. Murray, S. Tolley, J. Oliphant, H. Tolley, S. Lammert, E. Lee, D. Later, M. Lee, Journal of American Society of Mass Spectrometry, 19, 10, 1425–1434, (2008).


4. Trace Analysis in the Field Using Gas Chromatography-Mass Spectrometry; T. V. Truong et.al. Scientia Chromatographica, 6(1):13-26, (2014).


5. The Applicability of Field-Portable GC/MS for the Rapid Sampling and Measurement of High Boiling Semivolatile Organic Compounds in Environmental Samples; T.V. Truong et.al., Current Trends in Mass Spec, LC/GC Supplement, 20-26, July, (2016).


6. Torion T-9 Portable GC-MS Product Note, https://www.perkinelmer.com/lab- solutions/resources/docs/PRD_Torion-T-9- GCMS_012311B_01.pdf


Figure 8: Chromatogram of cocoa bean headspace from three sources. Note peaks shown with an asterix (*) represent compounds marked for quality control identification purposes


7. SPS-3 Sample Preparation Module for Torion T-9, http://www.perkinelmer.com/ lab-solutions/resources/docs/PRD_Sample_ Prep_Station(013095_01).pdf


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