Mass Spectrometry Based Analysis Reveals the Chemistry of Wine Bouquet
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Scientists from the University of Zaragoza, Spain, have developed an automated dynamic headspace (DHS) method that can provide a snapshot of the aroma compounds emanated from wine in conditions close to those found during wine tasting. They have then implemented the technique to see how this profile changes over time as it might in the glass during consumption.
The odour of food and drink is intrinsically linked to our taste perception and enjoyment, so being able to accurately quantify this information could have wide ranging applications. Previous evidence has suggested that measuring aroma compound concentrations alone is insufficient to accurately represent a wine’s odour as odorants may interact with the non-volatile matrix in the wine. This means that two wines with exactly the same aroma composition can produce headspace vapours (the part that would actually reach a consumers nostrils) with compositions that differ depending on the level and type of “aroma-binders” specifically present in each wine, altering a consumer’s perception.
Therefore, measurement strategies that focus on continuous monitoring of the headspace composition are required. Existing continuous monitoring methods, such as direct atmospheric pressure chemical ionization mass spectrometry (APCI-MS) or proton transfer reaction mass spectrometry (PTR-MS), lack the sensitivity required to monitor low level aroma compounds. Trapping aroma compounds in the headspace and analysing the concentrated chemicals by gas chromatography-mass spectrometry (GC-MS) improves sensitivity and selectivity but does not allow continuous monitoring.
In a recent study, researchers therefore developed a method using a dynamic headspace method combined with thermal desorption and GC-MS (HS-TD-GCMS) that enabled quantification of up to 40 relevant aroma compounds. Consequently, compounds could be categorised from polar, poorly volatile species that remained stable in samples over time (which accounted for around half of compounds present), through to non-polar highly volatile compounds that are lost rapidly.
The gathered data suggest that where data is given on compound concentration in the liquid phase, it should be accompanied by estimations of compound volatility to enable interpretation of their likely role in the sensory experience for a consumer. The study also confirmed that wine headspace continuously changes over time, which should cause alterations in the odour a consumer perceives.