Aroma analysis of vegemite 3. Data analysis and interpretationPosted: June 24, 2013
This is Part 3 of my vegemite aroma analysis series. If you haven’t read Parts 1 and 2, you can do so here and here. In a wonderful complement to my vegemite posts, Vittorio Saggiomo of Labsolutely has also done NMR and a microscopy video of marmite.
As a reminder, here is the output from the GC of the vegemite aroma analysis. There are many detection systems that can be coupled to the end of a GC which provide different kinds of information about the compounds which are analysed. In this case, the detector I used was a mass spectrometer (MS, or mass spec for short).
Mass spec is the most useful type of detector because it provides information about the structure of each molecule exiting the GC column, and often this information is good enough to deduce the identity of the chemicals in the separated mixture. At each point along the chromatogram (many times per second) the spectrometer collects a mass spectrum of the compounds present, which look something like this.
The mass spectrum is generated when the compound is ionised by electrons created within the mass spectrometer. Ionisation causes the molecules to fragment, and the mass and abundances of the fragments are measured by the spectrometer and provide key pieces of information about the chemical’s structure. In the spectrum above, each vertical line represents a molecular fragment and its relative abundance, with the number above it representing the molecular weight. Modern mass specs come with software that automatically searches huge libraries of compounds and finds likely matches to the spectrum collected. However, it is possible (and -[NERD ALERT]- fun!) to work it out by hand.
The matches collected by the software to the mass spectra of the vegemite aroma compounds, and their relative abundances are tabulated below.
|% total||compound||Associated odour|
|1.7||limonene||citrus, fruity, mint|
|0.2||benzaldehyde||almond, burnt sugar|
|0.8||benzeneacetaldehyde||cocoa, honey, spice, rose, lilac|
|0.1||phenylethyl alcohol||floral, rose|
|0.7||octanoic acid||fatty, pineapple, banana, sweat, cheese|
|12.5||octanoic acid, ethyl ester||fruity, fatty, floral, green, menthol, anise|
|0.1||2-phenylethyl acetate||floral, honey|
|0.2||2-phenyl-2-butenal||cocoa, floral, musty|
|0.5||sulfurol||sulfur, meaty, chicken broth|
|0.1||nonanoic acid, ethyl ester||fruity, rose, wax, rum, wine|
|1.6||n-decanoic acid||fatty, rancid|
|16.6||ethyl trans-4-decenoate||wax, leather, pear|
|2||n-decanoic acid||fatty rancid|
|43.8||ethyl decanoate||fruit, oil, sweet, wax|
|0.2||decyl acetate||floral, orange, rose|
|1.2||caryophyllene||spice, wood, cloves|
|0.2||3-methylbutyl octanoate||apple, coconut, grass, pineapple|
|0.8||beta selinene||woody, herbaceous, peppery|
|0.7||alpha selinene||amber, orange, pepper|
|1||dodecanoic acid||fatty, soapy|
|4.3||ethyl laurate||floral, soapy, wax, peanut|
|0.3||isopentyl pentadecanoate||floral, wine|
|0.9||tetradecanoic acid||flowery, woody|
|0.2||trans-nerolidyl formate||wax, floral|
|0.1||farnesol acetate||flowery, green rose|
|0.5||cis-9-hexadecenoic acid||wax, old-person smell|
|0.4||hexadecanoic acid ethyl ester||rancid|
|0.1||octyl 2-phenylethyl ester oxalic acid||citrus, fruity mint|
Based solely on the aroma descriptors I was able to find in online odour chemical databases, I think that the chemical ‘sulfurol’ probably contributes significantly to the odour of vegemite.
Chemical structure of sulfurol (2-(4-Methyl-1,3-thiazol-5-yl)ethanol).
Other compounds of interest that were detected in the aroma analysis are;
- Niacinamide: a derivative of one of the B-vitamins that vegemite is loaded with.
- Caryophyllene: a compound common which contributes a peppery spiciness.
- Hexadecenoic acid: notable for the fact that ‘old person smell’ is attributed to this compound!
The compounds revealed in the analysis are not an exhaustive list of all of the chemicals contributing to the aroma of vegemite. There were many more small peaks in the chromatogram that I did not search the mass spectrum of. It’s also likely that some of the chemicals that contribute to the aroma of vegemite, do not give a visible signal in the chromatogram, or were not picked up by the SPME fibre.
It’s interesting to note that many of the aromas in the table above are described as sweet, fruity or flowery, which are certainly not words you would use to describe the aroma of vegemite. There could be several explanations for this;
- The odour thresholds for these chemicals may be quite high. That is, they may have to be present in large amounts in order for the odour to be detected.
- When odours from different chemicals are mixed together, the whole may not be equal to the sum of the parts.
- Some compounds smell different depending on their concentration, or may even vary from person to person.
- The mass spec library searching program may not have been able to correctly identify some of the chemicals.
More specialised aroma analysis by GC can include the use of an olfactory detection port (ODP). Here, once the mixture is separated by the GC, the effluent is split in two with half going to a conventional detector (such as an MS) and the other half to the ODP or ‘sniffing port’ where an aroma analyst can smell what is exiting the column and assign odours to specific compounds.
Olfactory detection port from gerstel.com
I hope you’ve enjoyed this 3-part series on the chemical analysis of vegemite aroma. Thanks once again to Chris Slape for the inspiration, and if you have any questions, comments or ideas for future analyses please leave them below.