Last Month's Most Accessed Feature: Instant coffee aroma: Blend profiles by proton transfer reaction mass spectrometry

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  • Published: Sep 22, 2015
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Coffee aroma and mass spectrometry

Analysis of the aromas of different mixtures of instant coffees by proton transfer reaction mass spectrometry has shown that the profiles can be predicted accurately, unveiling a new product development tool for the food industry.

The aromas of coffee during roasting have been studied extensively but less attention has been made to instant coffees that have been prepared by spray drying or freeze drying. Instant coffee is a highly popular consumer product representing high income for coffee producers and retailers and a lot of development has been carried out to produce the blends that end up on sale.

But what of their aromas? They have been carefully chosen to provide different characteristics to the coffee drinker but which compounds are responsible for the specific distinctive brands? In general, scientists use GC/MS to characterise the aroma profiles but a team from Italy and the UK has taken a novel approach with the introduction of proton transfer reaction mass spectrometry (PTR MS) to the scene.

Andrea Romano and colleagues from Fondazione Edmund Mach (FEM), San Michele all'Adige and the Free University of Bolzano in Italy, and Mondelez UK R&D, Banbury, and Reading Science Centre (RSSL) in the UK thought that this technique would allow the easy combination of static and dynamic headspace analysis. The latter would follow the evolution of the aromas second by second after the addition of hot water to the coffee.

Blended instant coffees

Ten different blends containing two or three components were prepared by mixing different proportions of three instant coffee powders. Their aroma profiles were measured straight after adding hot water in experiments that mimicked above-the-cup conditions. The volatiles emitted from the coffee solution were analysed on a commercial PTR time-of-flight instrument that afforded high-resolution capabilities to aid confident compound identification.

For static headspace analysis, the coffee solution was kept at 60°C in a closed container for 30 minutes before being connected to the mass spectrometer inlet. For dynamic analysis, the background signal was measured for 100 seconds before the addition of hot water. The headspace above the coffee was then monitored over a further 500 seconds.

The mass spectral signals from each peak from the static procedure were converted to concentrations and the data were subjected to principal components analysis. A two-component plot clearly showed that the samples could be separated according to the composition, be they one-, two- or three-component samples. The classes of compound corresponding to the discrimination were alcohols, carbonyls, esters/acids, furans/pyrans, phenols, terpenes, sulphur compounds and N-heterocycles.

The PCA plot originating from the dynamic analysis confirmed the results from the static experiments, with the addition of time resolution for each of the mass spectral peaks. The discrimination between blends was maintained over the analysis period, so that a spot check at any time would still be able to reveal which of the ten blends was present.

Predicting aroma profiles

Given that the headspace compositions were unique for the various blends, the team went on to show that the reverse was also true: that the volatile profiles could be predicted from the make up of the blends. This was made possible using a simple calculation based on the proportion of each component in the blend and their individual release profiles.

The ability to foresee the aroma profile will provide a valuable aid to coffee producers and blenders who are striving to produce new and different products for their customers. The capacity of the PTR TOFMS system to process the complex data on a second-to-second basis, combined with the data analysis tools, is a powerful tool for the food industry.

It is reasonable to assume that the same system can be applied to the analysis of other kinds of dehydrated products like powdered soups and to different types of hot beverages such as tea and other infusions.

Related Links

Journal of Mass Spectrometry 2015, 50, 1057-1062: "Static and dynamic headspace analysis of instant coffee blends by proton-transfer-reaction mass spectrometry"

Article by Steve Down

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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