Coffee headspace

Bicchi, C., loti, C., Rubiolo, P. and Sandra, P. (2002) Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE) and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew. J.Agric. Food Chem. 50, 449-459. 

Source Identified as a volatile constituent released by fresh coffee beans Coffea canephora variety Robusta) at different stages of ripeness (Mathieu et ah, 1998). Also identified among 139 volatile compounds identified in cantaloupe [Cucumis melo var. reticulates cv. Sol Real) using an automated rapid headspace solid phase microextraction method (Beaulieu and Grimm, 2001). 

Fig. 15.3 Dynamic headspace MDGC analysis of three coffee beans, a Chromatogram of precolumn showing heart cuts at retention of peasy-like odours detected by sniffing the eluent from the precolumn, b Heart cut from normal beans on the main column, c Heart cut from defective beans...

An alternative to chemical ionisation is resonant (and non-resonant) laser ionisation methods [179], i.e. selective and soft laser photoionisation, such as REMPI. A particularly interesting setup is the combination of REMPI with TOFMS for monitoring coffee brew headspace. This chapter deals with technical features and applications of time-resolved analytical methods with particular focus on PTR-MS and resonant and laser ionisation methods (REMPI-TOFMS). 

Table 15.4 Proton affinities of the constituents of clean air and of various volatile organic compounds. All volatile organic compounds with a higher proton affinity than H2O (166.5 kcal/mol) will be protonated with a very high efficiency when colliding with H3O+. This is the case for most of the volatile organic compounds in the headspace of coffee, with the exception of the natural constituents of clean air. In contrast, if NH4 is used as a chemical ionisation agent, only compounds with a proton affinity exceeding 204.0/kcal mol are ionised below dotted line). (Adapted from [190]) ...

The success of PTR-MS triggered interest in further improving its performance. Indeed, PTR-MS is a one-dimensional technique, and ions from a complex headspace, e.g. coffee, can often only be tentatively assigned. Ions from different compounds (parent and fragment ions) can overlap in PTR-MS and prevent an unambiguous identification of VOCs in a complex mixture [198]. There-... 

As an example, the novel setup was applied to the characterisation of coffee headspace as a complex food system Basically, an aliquot of the headspace is trapped in defined time periods on several Tenax adsorbents for characterisation by GC-MS. Figure 15.17 shows the simultaneously recorded total ion counts of the EI-MS (top frame) and PTR-MS (bottom frame) for VOCs trapped on the first Tenax cartridge. The GC-separated pure compounds are identified... 

Fig. 15.17 Simultaneous EI-MS (top trace) and PTR-MS (bottom trace) total ion coimt analysis of coffee headspace. Identification was based on MS spectra obtained at 70 eV and the retention index of the reference compounds. (Adapted from [199])...

Yeretzian, C., Jordan, A., Lindinger, W. (2003) Analyzing the headspace of coffee by proton-transfer-reaction mass-spectrometry. Int. J. Mass Spectrom. 223-224 115-139. 

Zimmermann, R., Heger, H.J., Yeretzian, C., Nagel, H., Boesl, U. (1996) Application of laser ionization mass spectrometry for online monitoring of volatiles in the headspace of food products roasting and brewing of coffee. Rapid Commun. Mass Spectrom. 10 1975-1979. 

Holscher, W. and Steinhart, H. (1992) Investigation of roasted coffee freshness with an improved headspace technique. Zeitschriftjur Lehensmittel-Untersuchung und -Forschung, 195, 33-8. 

Comparative aroma dilution analyses of the headspace of aqueous solutions, containing either the total volatiles isolated from a fresh coffee brew or these volatiles mixed with the melanoidins isolated from coffee brew, revealed drastic losses of odorous thiols, 2-furfurylthiol, 3-methyl-2-butenethiol, 3-mercapto-3-methylbutyl formate, 2-methyl-3-furanthiol, and methanethiol, in the presence of melanoidins.509 The first compound was affected most, the reduction being 16-fold, and was accompanied by an overall reduction in roasty-sulfury aroma. The rapid loss of thiols was confirmed by stable-isotope dilution analysis. [2H]-NMR and LC-MS gave strong evidence that the thiols become covalently bound via Maillard-derived pyrazinium compounds. 

In earlier work with unfractionated coffee melanoidins, Hofmann el al.510 had already shown significant reductions of thiols in the headspace above aqueous model systems on addition of melanoidins, whereas aldehydes remained unaffected. 

Russo, M.V., Goretti, G., Liberti, A. Direct headspace gas chromatographic determination of dichloromethane in decaffeinated green and roasted coffee. J. Chromatogr. 465, 429 33 (1989)... 

Alternatively, one can convert the adsorption system into a partition system by adding a displacer to the sample in the vial headspace. One typical example is the determination of residual halocarbon solvent in decaffeinated instant coffee using an excess of water as displacer [45]. For analytes adsorbed on activated charcoal — which is used in personal monitoring tubes — benzyl alcohol is an effective choice for desorbing the volatile analyte [49,64]. 

SPME can also be used to extract target analytes from food and drug samples. Thus, it has been employed for the extraction of caffeine from coffee and tea [225], and for that of volatile impurities in drugs. Headspace SPME has also been tested for flavour analysis in foods. Thus, the SPME/GC/TOF-MS tandem was successfully used for the rapid analysis of volatile flavour compounds in apple fruit. The sample (300-450 g of apple) was subjected to static headspace sampling for 4 6 h in order to allow the volatiles... 

Shimoda, M. and Shibamoto, T. (1990) Isolation and identification of headspace volatiles from brewed coffee with an on-column GC-MS method,/. Agric. Food Chem., 38(3), 802-804. 

Mayer, F., Grosch, W. (2001) Aroma simulation on the basis of the odorant composition of roasted coffee headspace. Flavour Fragrance J. 16, 180-190... 

Figure 14. Detection of some volatiles emitted during roasting of 6 coffee beans. Six green Arabica coffee beans were roasted at 185°C, and headspace VOCs were monitored by PTR-MS the ions monitored and the corresponding VOCs are indicated. Data replotted from Ref. [30]. 

Procida et al. (1997) used dynamic headspace GC-MS to characterize the aroma volatiles of green arabica and robusta coffees (six varieties of each). They declared that robusta varieties have a higher content of methanol, acetone, pyridine, methylpyrazine and furfural, and that methyl formate, /cr/-butyl alcohol, and furfuryl alcohol are almost exclusively found in robustas. When looking at the figures, the conclusions are not as clear-cut. They identified 12 original constituents, mainly hydrocarbons and alcohols. 

Pollien et al. (1998) have thus compared headspaces of a brew and of an instant coffee and could detect a new key compound, 1-nonen-3-one (Section 5,D.36) and confirm the aroma impact of other compounds. 

White (1995), not for a sensory analysis but mainly with a view to determining coffee adulterations, used the data of combined headspace GC and high-performance LC for multivariate analysis. Principal component analysis visualized the relationship between samples, and the outlying samples could be identified. The method could be an additional tool for classification and quality control of coffee products. 

Identified in roasted coffee by Merritt and Robertson (1966) and in a brewed arabica (after liquid-liquid extraction with pentane or supercritical-fluid extraction) by Ramos et al. (1998). It has been found in the headspaces of six green arabicas and six green robustas by Procida et al. (1997). 

These were identified by Merritt et al. (1970) in headspace analysis of green and roasted arabica and robusta coffees. 

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