FRAGRANCES 49
human nose is currently a powerful tool, with the aim of taking advantage of the complementarity between the high sensitivity of the olfactory system and the robustness of instrumental analysis. This integration between the chemical and sensory components of an odour can be achieved by gas chromatography and mass spectrometry coupled to an olfactory port, an instrument known as GC-Sniffing-MS. This technique allows a specific odour to be broken down into each of the volatile compounds that form it, for its individual identification and quantification, as well as to obtain sensory information of each molecule. The GC-Sniffing-MS technique begins
with a separation process by gas chromatography (GC) of the different molecules present in an odour sample. Once separated, part of these molecules is directed to the mass spectrometer (MS) while the other is bypassed to an odour port (Sniffing). In this way, as soon as the MS identifies and quantifies each volatile compound, an expert evaluates them sensorially, in descriptive and intensity terms. The MS detection limit can be as low as a few parts per trillion (ppt) in some cases. It is also the case that molecules below the instrument detection limit are still detected by the human nose. With a correct sensory description of the compounds present in concentrations too low for the MS, increases the possibility of refining the method for their chemical identification. Combining the responses of a chemical
detector with that of a sensory expert, we can: l Identify the compounds that are relevant in relation to a particular odour;
l Determine the contribution of each of these compounds to the odour in question;
l Verify to what extent the compounds responsible for this odour, sensorially perceived individually, can be detected by chemical analysis (the human nose is usually more sensitive and discriminatory than instruments). There is another analytical technique
that, without having detection limits as low as the GC-Sniffing-MS, has the advantage of identifying the presence of volatile compounds at parts per billion (ppb) level in a matter of few minutes. This is gas chromatography and ion mobility spectrometry (GC-IMS). Another very interesting aspect of this technique is that it allows to compare differences and similarities between fragrances (“original” versus “inspirations”) in terms of their chemical composition in a qualitative and/or quantitative way, and to contrast these results with their sensory perception. GC-IMS is widely used to identify traces of substances and compositional differences
September 2020
in gaseous phases. The results can be visualised through molecular profiling on 2D diagrams. Finally, it is important to highlight that
the measurement of odours can also be based on other techniques that focus exclusively on the sensory evaluation of the overall smell of a product, and not so much of its components individually. These techniques are based on the response of trained panels, who are previously calibrated and selected according to their sensory acuity. There are different quantitative and qualitative odour parameters that can be measured: concentration, intensity, hedonic tone, attributes, polarity profiles, etc., by following different standardised methodologies. In addition to these methods that focus mainly on the descriptive and/or discriminatory odour evaluation of products, other techniques with a more effective approach are also used, where normally untrained individuals (naïfs) that are representative of the final consumer participate.
Evaluating rose One of our main activities is focused on the evaluation of a wide range of products and raw materials for the cosmetic and perfumery sector. A recent example is related to a study of the aroma of using one of the techniques previously
mentioned, GC-Sniffing-MS. Roses are used as raw materials in perfumery and food industry. Its characteristic smell is globally known and recognised, being one of the aromas that we can more easily identify and describe. However, there is a wide variety of types of roses and each of them has a specific molecular composition with a particular odour. The wide demand for this raw material, but also for rose aroma reproduction purposes, increases the need to know the key chemical compounds that contain each aroma. The objective of this work was to identify the compounds responsible for the smell of the petals of a specific type of rose. Thanks to the application of the GC-Sniffing-MS analysis, 61 volatile compounds were sensory detected, of which a total 43 compounds could be chemically identified. It was found that the main contributors to the petals aroma were different alcohols, such as certain isomers of citronellol (characteristic of citronella and rose oils) and phenethyl, as well as (-)-cis-tetrahydro-4-methyl-2-(2- methyl-1-propenyl)-2H-pyran, also known simply as rose oxide, which is the one that gives the most characteristic smell of this flower. Other compounds were also perceived less intensely, such as cis- geraniol, phenethyl acetate, 3-methyl-2-(3- methylbut-2-enyl)furan (also known as rose furan), benzyl alcohol, among others.
Conclusion In summary, odour measurement techniques are useful for improving commercial products so that positive emotional experiences in consumers can be generated. The selection and application of the appropriate method allows the presence or absence of certain compounds relevant to the odour of a certain product to be identified, the longevity of a fragrance to be tested, or the odour reduction capacity of a certain process to be measured and, ultimately, satisfy all kinds of demands from the cosmetic sector in the olfactory sensory optimisation of its products.
PC PERSONAL CARE EUROPE
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