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Food Analysis: Coffee

Coffee aroma: from roasting to brewing and headspace analysis

From the roasting of coffee beans to different types of brewing (filter, espresso and instant coffee), from real-time headspace to direct nosespace air sampling.

Virtually everything in the field of coffee analysis has successfully been investigated with IONICON PTR-MS instruments. Here, we only give two examples of the endless possibilities PTR-MS provides.

When PTR-MS tastes coffee

One of the first coffee studies that found great response in scientific as well as in non-scientific media was published by Lindinger et al. in 2008

This study by the Nestlé Research Center in Switzerland using IONICON PTR-MS was a major step forward in terms of correlation of sensory with instrumental results. The scientists were able to develop a robust and reproducible model to predict the sensory profile of espresso coffee from instrumental headspace data.

The analytical study and sensory profiling were performed utilizing different commercially available espresso coffee products. Online analysis with IONICON PTR-MS was used to obtain chemical information about differences in composition of the coffee headspace characterizing the different coffee blends. In addition, an expert panels trained for coffee tasting described each sample by scoring ten key flavor attributes on a 10-point scale. Subsequently, the overall sensory description of each sample was correlated with the analytically obtained differences in chemical composition in order to develop a statistical tool to predict the sensory profile based on analytical data. In a second step, the prediction was validated using a new series of coffee blends, which differ in the aroma profile and which were not included in the development of the predictive tool. The overall sensory prediction of the new blends based solely on the analytically generated data show a great match with the sensory profiles independently obtained by the expert panel.

This novel and efficient approach of characterizing the aroma of coffee blends by on-line PTR-MS analysis may shorten the time required for the development of new products and improve quality control in a more automated and objective manner.


High-resolution high-sensitivity coffee nosespace analysis

In food and flavor science researchers are often confronted with highly complex matrices. Thus, in order to separate compounds of interest from other compounds which share the same nominal m/z but have a different chemical composition (isobars), high mass resolution is of utmost importance.

To demonstrate the benefit of TOF based IONICON PTR-MS instruments' outstanding resolution we analyzed the nosespace of a person who had consumed some freshly brewed coffee. It is well known that vanillin and 4-ethylguaiacol are important isobaric aroma compounds at nominal m/z 153 (protonated molecules).

However, by looking at the mass spectrum around m/z 153 one can see that there are in fact four ions which share this nominal mass (black line). For a low resolution instrument all four ions would be merged into one broad mass spectral peak and only the intensity of the sum of them could be measured. The high mass resolution of the PTR-TOF 6000 X2 enables separation of all four ions. With IONICON's sophisticated data processing software the intensities are automatically deconvoluted (grey and blue lines; the orange line is the sum of the deconvoluted peaks, which perfectly reproduces the original data) and vanillin and 4-ethylguaiacol can be quantified independently, without parasitic influence of the two additional isobars.

High sensitivity is particularly important when compounds of extremely low abundance have to be quantified with high time resolution. Utilizing the high sensitivity PTR-TOF 6000 X2 we analyzed the nosespace of a person before (blank) and after drinking freshly brewed coffee. In the figure concentration values of 3-mercapto-3-methylbutyl formate at m/z 149.063 are shown during this experiment with a time resolution of 700 ms (time resolutions down to 100 ms are possible). Although this important aroma compound is present only in trace concentrations below 1 ppbv, the high sensitivity and low limit-of-detection of the PTR-TOF 6000 X2 allow for online quantification of the aroma development over numerous breath cycles after swallowing the coffee in real-time.