Variation in odor detection thresholds determined by charm analysis

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Abstract
Variation in odor detection thresholds for four groups of individuals, cross-classified by sex and age, was determined using seven standard aroma compounds: ethyl butanoate, ethyl 2-methylbutanoate, ethyl hexanoate, 1,8-cineole, menthone, l-menthol and l-carvone. These compounds were selected for study because they are all naturally occurring food constituents, and specific anosmia has been reported for some of them. In this study, odor detection thresholds were determined using charm analysis. The technique presents a sequence of pure aroma compounds in a stream of humidified air for subjects to smell. During a timed sniffing episode, the subject records the instant each odor is detected and the instant it disappears. Each odor stimulus is identified and characterized by its specific presentation time. Analyses are repeated at several dilutions of the stimulus mixture until no odors are detected. Response data for each odor are combined over all dilutions to yield odor-activity units called charm. Charm values are proportional to the amount of stimulus and inversely proportional to the subject's threshold. Results of this experiment show that charm analysis is a reproducible method for determining gas-phase odor detection thresholds. Differences in thresholds between subjects were not the same for all seven compounds. None of the thresholds were influenced by sex, whereas the threshold of l-carvone was affected by age and significant threshold differences between individuals of the same sex and age were found for menthone, l-menthol and l-carvone.