Palette odorants

Our odor communication system is based on the belief that there exists a set of palette odorants that can be mixed so as to mimic (up to a certain tolerance) any desired odor perception. Since to the best of our knowledge such an odorant palette has never been realized, the belief in its existence requires some justification. We start with a somewhat philosophical argument, and then provide some experimental observations to support it.

Relevant research indicates that we may assume that if two different stimuli elicit identical response of the ORs, the human perception thereof will be identical. Thus, it is the response of the receptors that has to be mimicked. An

incoming stimulus elicits a spatio-temporal response of the olfactory nerve cells in the epithelium. This response is the combined result of many factors (such as the type of the odorant, its concentration, and its temporal behavior), and it reflects the entire available information regarding the specific stimulus. This information is encoded into the odorant vector dB, which is considered to be the input for the cerebral analysis process. Since this process ends up with the ability to classify the odorant, to estimate its concentration, and to describe it, all this information must be somehow included in the response pattern, yielding the conclusion that identical response patterns will result in the same sensation regardless of the way they were formed. It is now reasonable to assume that any such set of responses can be viewed as a (possibly nonlinear) superposition of patterns, which, when deciphered, can be reformulated as mixtures of suitably chosen palette odorants. Thus, if we can prepare a mixture of palette odorants, whose collective effect on the olfactory nerve cells is similar to the effect of the original odorant, the perception of the mixture will very closely resemble the perception of that odorant.
The fundamental experimental observation that should be considered here is the fact that a mixture is usually perceived by humans as a new odor. This is actually experienced by every individual on a daily basis, with the distinct aroma of food products, beverages, coffee, perfumes, etc., all being odorant mixtures comprising usually hundreds of different odorous volatile chemicals.

Furthermore, the number of glomeruli activated when sniffng a mixture is similar to that activated when sniffng pure chemicals. Similarly, the number of odor qualities perceived by a human panel responding to a mixture is similar to that perceived when responding to pure chemicals. A typical smell is adequately described by 100 unique compounds on the average, then it would drive the number of palette odorants to be impractically large. Fortunately, this is not the case. It is known that even the most complex odors can be mimicked by mixtures of a relatively small number of ingredients. This is nicely seen in the food industry, where people are interested in generating certain smell perceptions using simple artificial blends, known as aroma models. Very complex aromas, such as those in wines, coffee brews, tomato paste, boiled beef and the like, are made of mixtures of many hundreds of chemicals. Yet, certain techniques have been designed to extract

those compounds that have the strongest impact on the smell, and only those are used in the aroma models. Typically, the original smell is reproduced with 10-30compounds at most.