Our nature is the first and the most powerful inspiration for people who create something new, including scientists. Most of us love the odour of fresh roses, ripe strawberries and forest after rain. When the odorous compounds are emitted into the air and further sensed by our nostrils, we can scent them. Scientists are able to isolate and replicate such compounds in laboratories, since the naturally occurring compounds are the most expensive. For instance, natural absolute of jasmine costs £3000–5000 per kilogram, the nature-identical materials (1) and (2) cost £300–500 per kg and the simpler cyclopentanone derivatives (3–5) £10–50 per kg (Fig. 1).[1]
Figure 1. Compounds with a jasmine scent
Sense of smell (i.e. olfaction) is the most complicate of all senses: it is combinatorial and is based on a specific pattern of signals from the olfactory nerves to the brain. The human nose has roughly 400 types of olfactory receptors that can detect at least 1 trillion different odours[2], with as many as 1,000 genes coding for olfactory receptors in the mammalian (600 genes are nonfunctional - pseudogenes).[3] Olfactory receptors recognize multiple odorants, and each odorant is recognized by multiple receptors, however there are specific anosmias and inabilities to detect a particular odour (e.g. musk, sandalwood, ambergris, urine). Furthermore, similar chemical compounds can possess the odour of a particular object, although each of them will have distinct properties and application. For instance, the Givaudan catalogue have the following proposals for jasmine odours:
The classical methods of isolation, such as extraction and distillation frequently produce, especially in the case of flowers, an extract that does not reflect the smell of the flower. Moreover, they are comparatively cheap and require sufficient quantity of sources. Do you know there is a technique eligible to catch the odour compounds that are present in the air surrounding various objects? And that this technique was developed approximately 40 years ago? In fact, big companies specialized in producing fragrances and flavours have special methods to discover new odorous compounds.
Figure 2. Headspace technology[4]
The name of this marvellous technique is headspace technology. It is non-destructive and able to trap the fragrant volatiles of an exotic flower directly in its natural environment[5], although techniques like this yield an amount of desired concentrates so tiny that the analysis of the components has only become possible over the last 20 years. After collecting the concentrates, the analysis is performed using gas chromatography, mass spectrometry, or NMR.[1]
In 1993, Surburg and his colleagues applied two different headspace techniques to obtain volatile components of the lily of the valley:[1]
Recently, French laboratory published the monitoring of the release of trans-anethole and related essential oils from the series of novel low melting mixtures using multiple headspace technology.[7] Another example can be presented by Greek scientific group that used headspace solid-phase microextraction for examining the volatile fraction of wines.[8] Hence, the headspace technology in different variations is popular nowadays.
The most famous manufacturers of flavours and fragrances patented their variations of headspace technologies:
The following video will share the insight of headspace technology:
Summing up the described headspace technology, it seems to be quite mythical at first glance but, in fact, it is understandable and not very complicated. Now we know how to figure out the structure of the most pleasant note of our beloved flower.
References:
(1) Sell, C. S. The Chemistry of Fragrances - From Perfumer to Consumer 2nd Edition; Royal Society of Chemistry, 2006.
(2) Morrison, J. Human Nose Can Detect 1 Trillion Odours. Nature 2014. https://doi.org/10.1038/nature.2014.14904.
(3) Gilad, Y.; Lancet, D. Population Differences in the Human Functional Olfactory Repertoire. Mol. Biol. Evol. 2003, 20 (3), 307–314. https://doi.org/10.1093/molbev/msg013.
(4) https://www.givaudan.com/our-company/rich-heritage/odyssey-flavours-and-fragrances/science (Accessed on May 26, 2020)
(5) https://en.wikipedia.org/wiki/Headspace_technology (Accessed on May 26, 2020)
(6) Hui, Y. H.; Chen, F.; Nollet, L. M. L.; Guiné, R. P. F.; Le Quéré, J. L.; Martín-Belloso, O.; Mínguez-Mosquera, M. I.; Paliyath, G.; Pessoa, F. L. P.; Sidhu, J. S.; et al. Handbook of Fruit and Vegetable Flavors; Hui, Y. H., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2010. https://doi.org/10.1002/9780470622834.
(7) El Achkar, T.; Moura, L.; Moufawad, T.; Ruellan, S.; Panda, S.; Longuemart, S.; Legrand, F.-X.; Costa Gomes, M.; Landy, D.; Greige-Gerges, H.; et al. New Generation of Supramolecular Mixtures: Characterization and Solubilization Studies. Int. J. Pharm. 2020, 584, 119443. https://doi.org/10.1016/j.ijpharm.2020.119443.
(8) Terpou, A.; Ganatsios, V.; Kanellaki, M.; Koutinas, A. A. Entrapped Psychrotolerant Yeast Cells within Pine Sawdust for Low Temperature Wine Making: Impact on Wine Quality. Microorganisms 2020, 8 (5), 764. https://doi.org/10.3390/microorganisms8050764.