Slide1: In order to be a good scent, molecules must be moderately volatile – in practice this means a RMM of under 300. They must also be able to bind with scent receptors – an area the size of a postage stamp buried deep within the nose. Humans have a poor sense of smell compared with other animals, but most of us can smell a strawberry at concentrations of only 10 ppm. The nose contains about 10 million olfactory receptors divided into 30 different types working together. When a receptor reacts with an incoming molecule, it undergoes a conformational re-arrangement which sends an electrical signal to the brain. Signals from all the receptors are combined and compared with profiles stored in memory to identify the source. Perfumes……the nose Slide2: Perfumes Traditionally, the perfume industry classifies the design of commercial products in terms of three ‘notes’.
The highest notes, the most volatile compounds which reach the nose in the first few minutes, are usually citrus and fruit based. Typically, these are esters (such as amyl acetate with its characteristic pear drop flavour) or aldehydes (phenyl acetaldehyde smells of lilacs and hyacinth). First impressions are created by the high notes.
Middle notes, with a slower rate of evaporation, include scents such as jasmine (amyl salicylate) and other florals. Middle notes are the most noticeable component of perfumes and tend to appear after about 15 mins.
Base notes are slow to evaporate and comprise the ‘woody’ smells such as musk (usually associated with the compound civetone) and amber. Base notes create the ‘lasting impression’. They appear after about 30 mins and may last for several days. Most compounds used in the industry are either esters or terpene derivatives. ‘Essential oils’ is the description first given by chemists to classify the latter. This refers to their being ‘essences’ of natural products and does not indicate that they are in any way indispensable. Terpene itself is a dimer of isoprene, Slide3: Perfumes A perfumer will have over 4000 plant and animal extracts and over 2000 synthetics from which to create a new mixture. It takes 5000 kg of petals to create 1 kg of rose oil. The expense and public attitude to animal products dictate that most extracts have been replaced by their synthetic versions.
Modern perfumes are blends of chemicals dissolved in alcohol, usually at concentrations of between 10 and 25%. Colognes are much more dilute (and thus less costly) versions of the same formulae – typically 1 to 5%.
The word ‘perfume’ originates from the Latin per and fumus, meaning ‘through smoke’ – a reference to scents being carried via incense burning in sacred ceremonies.
Virtually anything can be used as a perfume, we mention here only the most usual ones and ignore speciality syntheses (all of which exist) such as gun smoke, dinosaurs, Zulu warriors, striking flints or latex rubber!
On the next pages are just a few of the myriad scents and flavours used in commercial materials – the exact composition of these (often with over 300 components) are closely kept secrets but the principal ingredients are readily identified. Slide4: Perfumes Try naming these compounds for yourself! Slide5: Perfumes Slide6: Perfumes