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Odor Among Aromas

By: Larry Nielsen
Posted: June 9, 2008, from the June 2008 issue of GCI Magazine.

Those who work in the perfumery industry know that much can go wrong in the world of scent. For example, raw materials can vary in their aroma quality, oxidation can change a material’s aroma profile as it sits on a shelf waiting to be purchased and packaging can interact with components in products, altering aroma quality. In addition, a variety of undesirable odors can creep into products during the production and distribution process, and off-odor is a common problem for a variety of consumer goods. In turn, negative olfactory and consumption-changing experiences are common.

When an odor problem occurs and the consumer complaints come in, the usual first step is for the product manager to order some kind of analysis to quickly identify the odor. The analysis typically chosen is gas chromatography coupled with mass spectrometry (GC/MS), and this technique is ideal for the identification of chemical compounds in a product. Trace level compounds can be isolated by the GC part and identified by MS. However, the GC/MS process cannot “smell” the sample, nor can the much-touted electronic nose technique.

With these analyses, there is no correlation of the detected compounds with their respective odors, and there may be hundreds detected. What this means is that although you can identify the compounds, you do not know which one is causing the offending odor. A lab may work months on the problem using these techniques, but the chances of correctly identifying the odor are slim. The reason for the lack of success is that those techniques alone cannot make the correlation between odor and chemical identification. Only the human nose connected to a normally functioning brain can distinguish among all the chemical compounds in a sample as to odor character and intensity.

To “see” the odor among the aromas, specialized equipment must be utilized in conjunction with the human sense of smell. The general technique is called “sensory-directed odor analysis.” The process works by first collecting a sample and then completely separating each chemical compound from all the others. The collection process varies depending on the product being evaluated. These separated compounds may or may not have an aroma. When each individual compound exits from the instrument, it is sniffed by a human analyst, who describes its aroma character. At the same time, the analyst uses personal sensitivity to the aroma compound to give a subjective intensity for it in the sample under investigation. The final result of sniffing through a sample is an aromagram. This graph shows all volatile aroma compounds in the order in which they exit the instrument. Their intensity is shown by the size of the peak, and there is the associated aroma character with each peak. The aromagram ranks the importance of the aromas in terms of their intensities and, often more importantly, in terms of their character. Off-odors are quickly distinguished in the aromagram, and if they are intense, they are most likely contributors to the odor problem.

In addition to detection of aromas by the human nose, systems that use a mass spectrometer to simultaneously obtain the identity of the aroma along with its character and intensity are available, permitting fast resolution of odor problems that otherwise might take months, or might never be completed, using less sophisticated and integrated analytical systems.

Sniffing Out the Clues