48 FRAGRANCES
Aroma measurement in cosmetics and perfumery
n Rita Ribau Domingues, Luciano Vera, Alice Nauendorf – Olfasense, Spain
Smell is evolutionarily the most primitive sense and is related to our ancestral instincts. Being closely limited to the areas of the brain that control and regulate memory and emotions, odours – a more general term referring to pleasant (aromas) and unpleasant smells – directly affect our behaviour and mood. That is why an odour is a decisive factor in the acceptance or rejection of a product or material, which makes it a basic quality parameter. Smells are activators of our emotional
regions in the brain.
How do we perceive odours? It all starts when volatile molecules that cause an olfactory sensation penetrate our nose into the nasal cavity, and are captured by the olfactory epithelium where millions of receptor cells are present. Depending on the chemical structure and vibrational mode of the volatile molecules - the importance of both mechanisms is still being debated - the cells of the nasal epithelium convert the stimulation of chemical compounds into nerve impulses that are directed towards the olfactory bulbs of the brain. From the olfactory bulb, the odorific message is transmitted to other areas of the brain in two independent ways: the first is directed to the primary cortex, the area responsible for the integration of olfactory information at the conscious level. However, the second pathway reaches the piriformis cortex, a primitive area of our brain where the limbic system acts as an unconscious integrating centre for emotional responses (the amygdala), and for the storage and control of memories (the hypothalamus).
What is special about the olfactory sense? The olfactory system differs from the rest of our senses for several reasons, of which the neurological process described above gives it a unique dimension. The direct connection in the limbic system between the odour stimulus and the processing of experiences and emotions, explains the evocative capacity of a certain smell, which takes us back with great emotional intensity
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to lived moments, and even generates physiological responses in our body. A practical consequence of the particular
perception of the smell is that, in nearly no known language, except the Jahai spoken by some groups in Malaysia, there are words to describe it in a direct and precise way. If we want to do it, it is necessary to resort to foreign terms, often applied in a comparative and metaphorical sense, to define an odour as “delicate”, “strong”, “unpleasant”, or similar to “freshly cut grass”. The language of odours is, therefore, ambiguous and less robust, which is why the world of the sense of smell is characterised by the difficulty in its definition. However, given the importance of the olfactory phenomenon, various protocols based on scientific methods have been developed to analyse odours in an objective and repeatable way.
How is odour measured in cosmetic products? A fragrance has the power to generate an identity and evoke experiences associated with its characteristic aromas. These aromas correspond to mixtures, sometimes very complex, of volatile organic compounds (VOCs) present at a concentration in the gas phase higher than its olfactory
perception threshold. The knowledge of the chemical composition of fragrances and their interrelations with the olfactory sensation, allows us to develop and optimise formulas, investigate the presence and origin of unwanted odours (off-notes), characterise imitations, etc. Defining odour attributes is a difficult
task due to the variable nature of sensory experience. However, it is becoming increasingly feasible to apply objective methods for its study due to recent technological advances. Research is progressively being developed to generate sensitive/high-tech equipment and algorithms to mimic the human nose (e.g. bioelectronic noses), thanks to advances in nanotechnology, synthetic biology, artificial intelligence and machine learning. However, technological applications based on those are still limited. There is no analytical technique that is as sensitive for a significant number of key odorants as the human nose, also the importance of the perceptual part cannot be ignored. As mentioned above, smells are based on interpretations of sensations by the brain, based on the experiences of each individual. To overcome this limitation, the
integration of chemical analysis with the September 2020
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