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Odor Among Aromas

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

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Some of the most offensive odors that can occur in cosmetic products have sulfur in their molecular formula. Several projects have come to Microanalytics in which consumers have complained to the manufacturer of an unpleasant sulfur-based odor; a particularly notable project involved a skin cleanser that generated numerous complaints because of its “garlic” odor. The “garlic” descriptor indicates sulfur to a sensory analyst. When the sample was run and compared with a retained skin cleanser that did not have any trace of “garlic,” it was immediately clear that a single, intense off-odor corresponded exactly to the unpleasant odor. The instrument identified it as a sulfur compound, and showed that it was present at a very low concentration even though it gave a strong odor response to the whole product.

There were numerous aromas in the product, but the use of the sensory-directed odor technique quickly placed the focus on the bad odor. The odor was then traced to a raw material, and, because the identity of the off-odor was known, it was then possible to screen raw materials for the off-odor compound using conventional quality control techniques.

Development and QA

Sensory-directed odor analysis is a useful tool to resolve crisis-driven product quality problems. In some cases, the future customer acceptance of a product is at stake unless the odor can be removed quickly before the public has time to form a permanent negative impression. Another scenario for this type of analysis is its use in conjunction with the development of a new product.

When sunless tanning cream was being developed, it was noted that odors were generated under certain conditions. In one promising product under development, the odor was found strong enough to negatively impact consumer acceptance. The complex odor of the applied cream changed with time, and was hard to characterize except that it had a lot of food-like aromas—though none you’d want to eat.

Before the sample can be run, it first has to be collected, and this process combines both a low- and high-tech approach. In the sunless tanning cream example, the analyst applied the product to his own leg, and the site was wrapped in aluminum foil to contain the odor. A very small probe was inserted via a pin hole in the aluminum. The fibers within the probe collected the vapors, which were then transported to the analysis unit. A very small amount of fiber—less than 1 cubic millimeter—is all that was needed to collect the vapor sample. The fibers are then heated to 250°C, which releases the compounds individually and allows them to be measured and identified.