GRAS Flavor Chemicals— Detection Thresholds By John C. Leffingwell and Diane Leffingwell Leffingwell & Associates, Canton, Georgia ThereIativeintensiq o~inditidu~chemical odorats and flavorants is a subject that daily confronts those in- volved in the creation of fragrances and flavors. The actual measurement of such intensities has largely heen restricted to the detemlination of “threshold values of detection. ” This is the value determined by panelists (usually aminimum panel of sixteen or more) at which the odor or flavor of a “pure” odorant can be detected. The measurement of threshold values is dependent on a number of factors: [a) e~erimental methodology, (h) screening of panelists for specific anosmia, (c) experience of panelists, (d) pwity 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 publisbed values for detection thresholds-even reported from the same group of workers40 not always agreee exactly. Regarding methodology, sufRce it to say there are several generally accepted methods- g., the procedure described by Guadagni and Butteq#M), the procedure of Amcmref 1231and others. A case in point regarding tbe effect of methodolo~ on an odorant threshold determination is tbe example of Dama.scenone reported in 1978 by Ohloff on the components of Bulgarian Rose Oil(fi) (see ako footnote 126 relative to the original threshold report). “Continuing the determinations of threshold values of minor mmponents, Pickenhagen found that tbe actual threshold of 13-damascenone is by a factor of l@ lower than reported here (10 ppb). Tbe error is due to tbe fact that, at a certain level, which exceeds its threshold by a factor of around 1000. (Ldamascenone seems to have a fatiguing 0272-2&W91/CCO141 01$04.03/00431991AlkwdM4khiwCm
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GRAS Flavor Chemicals—Detection ThresholdsBy John C. Leffingwell and Diane LeffingwellLeffingwell & Associates, Canton, Georgia
ThereIativeintensiq o~inditidu~chemical odoratsand flavorants is a subject that daily confronts those in-
volved in the creation of fragrances and flavors. The actualmeasurement of such intensities has largely heen restricted
to the detemlination of “threshold values of detection. ”This is the value determined by panelists (usually aminimum
panel of sixteen or more) at which the odor or flavor of a“pure” odorant can be detected. The measurement of
threshold values is dependent on a number of factors: [a)
e~erimental methodology, (h) screening of panelists forspecific anosmia, (c) experience of panelists, (d) pwity ofodor/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 publisbed values for detection thresholds-even
reported from the same group of workers40 not alwaysagreee exactly.
Regarding methodology, sufRce it to say there areseveral generally accepted methods- g., the procedure
described by Guadagni and Butteq#M), the procedure ofAmcmref 1231and others. A case in point regarding tbe effectof methodolo~ on an odorant threshold determination istbe example of Dama.scenone reported in 1978 by Ohloff on
the components of Bulgarian Rose Oil(fi) (see ako footnote126 relative to the original threshold report).
“Continuing the determinations of threshold values ofminor mmponents, Pickenhagen found that tbe actual
threshold of 13-damascenone is by a factor of l@ lower thanreported here (10 ppb). Tbe error is due to tbe fact that, at
a certain level, which exceeds its threshold by a factor ofaround 1000. (Ldamascenone seems to have a fatiguing
0272-2&W91/CCO14101$04.03/00431991AlkwdM4khiwCm
FlavorThresholds
effect and stays in the mouth. Thus by determining thethreshold by a double triangle test against water, with
descending concentrations, tasters frequently indicate theproduct to be in tbe blank too. The now found threshold
concentration is 0.009 ppb and was determined using de.scending concentrations, ”
Now, this experiment also points out another prob-lem—semantics—is the value determined a “flavor
threshold or an “odor threshold?’ Ohloff appears to haveintermixed values determined b different methodologies
(fin some of his tabulations 37,86 and resolvedtbe problem
simply by labeling them as “threshold vafues,” This is &the case in other publications where reported “odor”thresholds may, in fact, be “flavor” thresholds. For the
purist, this may be incorrect, but in most cases, detectionthresholds determined by an acceptable procedure willprovide the practicing flavmist a starting point from which
to build his own judgments, Detection thresholds re-
ported and discussed here are restricted to determinationsin aqueous media,
For volatile non-ionizable odorants, such as
dama.scenone,we believetbat whetberdetectedby smelling(external) or by placing in the mouth (internal) that the
threshold determined is that of the “odor.” However, withmaterials, such as isovaferic acid or trimethylamine which
ionize in water—’’taste” as well as “odor” may complicate
the determination depending on technique. Similarly, non-volatile materials, such as caffeine and glycine, which haveno odor, can only be evaluated based on the flavor or taste.
Suffice it to say that inthetabulation presented in thisreview, we consider that the variations in reported “odor”
and “flavor” thresholds reflect primarily different method-ologies. However, one particularly disturbing factor is
prevalent in the literature, A numberof workers will simplylist chemicaf odor detection thresholds in publications and
not indicate which have been newly determined,redetermined or simply restated based on prior publishedwork,
If the values presented are consistent with earlierpublished values, of course, there is no concern, but when
athreshold vafuefor aproduct like benzafdeh de, whichhadpreviouslybeen acce tedas350ppb(10.45[ suddenly
?is stated to be 3500 ppb, 88) one wonders if this isa’’ty-pographicd” error or not. Similarly, the threshold vafue for2-methylpyrazine has recentfy been listed as 60 ppb(lO)
when earlier publications indicated it to be 60000ppb(32,120) and the lowest other reported vafue is 30000ppb,(124)
Selection of panelists for determination of thresholdvalues is of some interest since it is now generafly accepted
that women are more sensitive to odors than men. This wasdemonstrated by Koelega ( 118) and statistically seems tobe confirmed by The Naticmaf Geographic Smell Surveyconducted in late 1986.(47) Age of respondents afsoap-pears to play a major role in acuity, with definite decreasesoccurring past age 50.(47.112) A series of papers from theconference on “Nutrition and the Chemical Senses in
Vol.16,kmwry/Fekmy 1991
Aging” held in 1989 and published in the New YorkAcademy of Science Annals provides insi htintopossible
Ereasons forthis loss of sensitivity (112-11 ) Loss Ofsensi-tivity with age is not just restricted to detection thresholdlevels butalsotoim airmentofthe ability to discriminate
6Pfwdsandcxfors.(11 ,117) Inaddition,Amoore(38 )reportedthat screening of 764 laboratory employees for one or more
ofsixanosmiatypesresultedin3% to 477. specific anosmiain vwious (odor) categories, with a generaf anosmia to allodors of 0.2%, In particular, the “urinous” odor of 5-ct-
Androst- 16-en-3-one showed 47% of respondants as beinganosmic while the “mafty” odor ofisobutyrafdehyde showed36% anosmics and the nature identical musk omega-
cyclopentadecanolide (also known as Tbibetcdide orExaftolide), 12% anosmics (as measured with aqueoussolutions at sixteen times the “normti threshold level),
Thus, with the caveat that a threshold detection levelfor one inditiduaf is not atbresholdlevel for afl, we can now
begin to examine the utility of such reported values in the
Chadagni et. al(~)
world of thepracticin flavorist,
proposed the concept of “odorunits” as a measure to assess the relative importance ofindividual chemicaf components present in a more complex
aroma mixture. Since mOstfOOds cOnsist 0f70-9070 water,the odor unit (Uo) value is obtained by dividing the con-centration “C (in ppb) of the chemical odorant in water by
the thresold concentration “T (in ppb) for that particular
Pmf- & F!avOriSt/3
Flavor Thresholds
chemical in water.
U.= C/-rIn theory it has been presumed that tbe
probability of a chemical odor being detected
should be greater the larger tbe number of odorunits for that chemical that are present. This
concept bas been tested rather successfully byscientists at the Western Regional Research
Center of the USDA in Afbany, California for anumber of food flavors. Guadagni et al. (121)
also suggested that the odor unit value for amixture of volatile chemical odorants present in
an aroma mixture was equal to the sum of the
number ofodor unitsforeach ofthe individual
constituents.
UO (mixture) = Uol + U09. + U03 +
It should be recognizedthatthissimplistic
appr~ach is an approximation.For example,
TABLE1
MAJORVOLATILEAROMACONSTITIJENTS OF COOKED RICE (10)-----------------------------------------------------
linearMth .Oncentrationtllg)and any synergisticeffects constructthe odor unitvafuesare spread out in various
which may occur from tbe admixture of flavor chemicals journals (and in many cases are not reported in consistentcannot be accounted for by this approach. But, in the units—ppb, ppm, mgAiter, millimolesfmole, microgramabsence of anything better—and considering that, in most kilogram, molar concentrations and log molar concentra-cases, the odor unit approach works—this technique is a tions, etc.). In the table at the end of this article, we havevery vafuable tool for the flavor chemist. Utilization of the provided a series of detection threshold w-dues, all in theodor unit concept for assessing the relative importance of same units (ppb), so that a quick assessment as to theflavor chemicals determined in the anafpis of volatile relative strength can be made by those utilizing the table.chemicafs in a naturaf product now seems obtious. Why In preparing this article, we realized that without atthen has this procedure found such little actual use? least one practical example of the utility of using threshold
Many flavorists have been posed with the problem of data and the odor unit concept that this tabulation wouldduplicating the “natura~ aromtiflavor profile of a product
from compositional data determined by the highly so-probably gather dust on the shelves of most flavorists.
An example of using threshold data and the odor unitphisticated analytical techniques now available. But if one concept in constructing a flavor is shown for cooked rice.is faced with a chromatogram identifying 450 components Table I lists the quantitative values of 17 major compo-(many of which may not be GRAS), the easy solution is to nents of cooked rice (out of more than 100 reported in the
either forget the analysis and rely on the age-old art of pure literature). In this example (Butte~, 1988), all of the
creativity or to make a ve~ complicated flavor. If the components reported here are GRAS with the exception of
flavorist ignores the detailed anafysis he risks being labeled Z-acetyl-l-pymoline whose odor threshold value is known
as uncooperative, unappreciative and sin of all sins— to be 0.1 ppb.
unscientific.The concept of utilizing odor units and threshold
values at least provides botb the analytical scientist and TABLE 11
Accordingly, from the table we find that even thoughphenethyl alcohol is present at levels 150 times highertban2-acetylpyrroline, its odor unit vafue is only 1,5% as great,Obtiouslyfrom the number ofodorunits, 2-acetylpyrroline(which possesses a strong popcorn aroma) and 2,4-decadienal with its fatty, tallowy character are two of themajor flavor impact compounds of cooked rice, Since 2-acetylpyroline is not GRAS, the creative flavorist couldutilize either 2-acetylpyrazine, 2-acetyl thiazole or 2-ac@#pyridine as these all have similar odor profiles. Butwhich is mot cost effective? While none has a lower odorthreshold than 2-acetylpyrroline (0.1 ppb), at least basedon threshold data, it appears that 2-acetylthiazole with athreshold of 10 ppb is abetter choice than 2-acetylpymzine(threshold of62ppb). Onapurecostbasis, 2-acetylpyridine(threshold level of 19 ppb) is the least expensive choice,however, its flavor is somewhat less desirable.
Having made the decision to evaluate both 2-acetylthiazole and 2-acetyIpymzine in applications, oneneeds to know the amount required to (theoretically)match the odor value contribution of the 2-acetylpyrrolineto be replaced. In order to determine the concentration of2-acetylthiazole necessa~to have an odor unit value equalto the 2-acetylpyroline in Table I (a value of 6 odor units),one uses the equation
Concentration = Odor units x Threshold
wherein the thresholdvdue utilized is that of2-ace@hiamle(HIppb):
Utilizing this technique, two cooked rice flavors wereprepared with the goal of using no more than eight compo-nents.
Note that fortbe flavor chemicak employed (Table II),the units correspond to an exact replica of the amountsfound (in ppb) from the analytical values in Table I, withthe exception that the 2-acetylthiazole arid 2-acetylpyrazinehave been incorporated at levels which theoretically (basedon odor unit wdues) replace the odor contribution of thenon-GRAS component, 2-acetylpyroline.
The two flavors “A and “B were diluted to a 0,5%solution each in benzyl afcohol and compared in odor to acommercial sample of Basmati Rice extract. Sample “B”,aftbough slightly stronger, was extremely close in odorproffle to the commercial “aromatic” rice extract. Sample“A possessed a more fatty character that was consideredcharacteristic of non-aromatic cooked rice,
Sample “A was added during cooking to unscentedlong grain rooked rice at a level of 166 ppb and comparedto an unfortified control sample. The flavor of the fortifiedsample was judged to be well balanced and much richer inboth aroma and taste, but possessed none of the character-istic “nutty” notes associated with the scented Basmati orTexamati types.
Sample “B” was added during cooking to unscentedIonggrain cooked rice at a level of478 ppb; the flavor ofthissample was more aromatic, but not as “natural” in profileas sample “A. Panelists’ comments indicated that while itpossessed some of tbe notes of aTexamati sample, it lackedthe nutty intensity. Compared to the unscented controlrice, it was more aromatic, but slightly unbalanced.
Accordingly, with just two experiments, one of the twoflavors (Sample “’A), provided a ve~ good reconstitutedcooked rice flavor, Sample “B”, while not hitting the markinitially, was later modified into a Texamati-type flavor.
It should be noted that in the two synthetic rice flavors(Table II), the incorporation of 2-phenethyl alcohol andhexyl alcohol have negligible impact in the flavor and couldtheoretically be removed. Based on the odor unit concept,these two items contribute less than 0.5% to the sum of theodor unit values in these flavors.
In conclusion, odor detection threshold data can beuseful in making judgments on use levels in flavor cre-ation, as well as in planning flavor reconstructions. Withthe plethora of published data now available on the com-position of natural food aromas, utilization of Guadagni’sodor unit concept is an effective and inexpensive tool forsimplifying the otherwise difficult problem of converting acomplex flavor analysis into a “practical” flavor system.
In our labs, we have now collected threshold values invarious media for about 22’70of all chemicals which appearon the GRAS lists. Only detection thresholds in watermedia are protided in this tabulation.( 125)
Address Correspondence to John C. Lef8ngwell,LefRngwell & Associates, Route 1, Box 22, Arbor HillRoad, Canton, Georgia 30114
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Vol. 16, Jonuay/Febwmy I W I
I Flavor Thresholds I
Table Ill. Odor/Flavor Detaction Threshold Data in PPB (Water)
FEMA Odor Odor Flavor Flavor
No. Name Threshold References Threshold References