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Odor Detection Thresholds of GRAS Flavor Chemicals

by Diane Leffingwell & John C. Leffingwell

Background

The relative intensity of individual chemical odorants and flavorants is a subject that daily confronts those involved in the creation of fragrances and flavors. The actual measurement of such intensities has largely been restricted to the determination of threshold values of "detection." This is the value determined by panelists at which the odor or flavor of a "pure" odorant can he detected. The measurement of threshold values is dependent on a number of factors: (a) experimental methodology, (b) screening of' panelists for specific anosmia, (c) experience of' panelists, (d) purity of odor/flavor chemical, and (e) sex and age makeup of panel and (f) the media in which the odorant is evaluated.

Addressing these points, one should be aware that various published values for detection thresholds - even reported from the same group of workers - do not always agree exactly.

Regarding methodology, suffice it to say there are several generally accepted methods - e.g., the procedure described by Guadagni and Buttery (122), the procedure of Amoore (123) and others.

For volatile non-ionizable odorants, such as damascenone, we believe that whether detected by smelling (external) or by placing in the mouth (internal) that the threshold determined is that of the "odor." However, with materials, such as isovaleric acid or trimethylamine, which ionize in water -"taste" as well as "odor" may complicate the determination depending on technique. Similarly, nonvolatile materials, such as caffeine and glycine, which have no odor, can only be evaluated based on the flavor or taste. Suffice it to say that in the tabulation presented here, we consider that the variations in reported "odor" and "flavor" thresholds reflect primarily different methodologies.

Selection of panelists for determination of' threshold values is of some interest since it is now generally accepted that women are more sensitive to odors than men. This was demonstrated by Koelega (118) and statistically seems to be confirmed by The National Geographic Smell Survey conducted in late 1986 (47). Age of respondents also appears to play a major role in acuity, with definite decreases occurring past age 50 (47,112). A series of papers from the conference on "Nutrition and the Chemical Senses in Aging" held in 1989 (and published in the New York Academy of Science Annals) provides insight into possible reasons for this loss of' sensitivity (112-115). Loss of sensitivity with age is not just restricted to detection threshold levels but also to impairment of the ability to discriminate foods and odors (116,117). In addition, Amoore (38) reported that the screening of 764 laboratory employees for one or more of' six anosmia types resulted in 3% to 47% specific anosmias in various (odor) categories, with a general anosmia to all odors of 0.2%. In particular, the "urinous" odor of 5-alpha-androst-16-en-3-one showed 47% of respondents as being anosmic while the "malty" odor of isobutyraldehyde showed 36% anosmics and the nature identical musk omega-cyclopentadecanolide (also known as Thibetolide or Exaltolide), 12% anosmics.

Note that the term anosmia refers to ones inability to smell a certain odor.

A more complete review of this appeared in Perfumer & Flavorist , Vol. 16, No.1, 1-10 (1990) by J.C. and Diane Leffingwell.

A more extensive list of threshold values is found in Flavor-Base 2004.

Follow the links below to access the Odor Detection Threshold level table for numerous GRAS (Generally Regarded As Safe) flavor chemicals. References from this page and for the specific thresholds are found at the bottom of the table.