TM. Sensory Evaluation of Aroma Models for Flavor Characterization. Keith Cadwallader University of Illinois at Urbana-Champaign. Kenneth A. Spencer Award Symposium Kansas City Section of ACS October 27, 2008. Overview:. Rationale: why conduct sensory studies?. General approach.
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Sensory Evaluation of Aroma Models for Flavor Characterization
University of Illinois at Urbana-Champaign
Kenneth A. Spencer Award Symposium
Kansas City Section of ACS
October 27, 2008
General approach for performing model studies
identification by GC-MS, RIs and odor properties
AEDA, DHDA, GCO-H, post-peak intensity scaling
GC-MS with IS and SIDA methodology
calculation of OAVs from threshold data
selection of appropriate matrix
of aroma model
dose-response studies (descriptive analysis)
omission studies (n-1) with difference testing and descriptive analysis
• Impact (cause-and-effect relationship) of a single odorant
• (Re-)creation of an aroma system (model)
• Relative impact (or influence) of all aroma components on the aroma system
• Experimental design options
• Sensory methods of analysis
Some limitations in methods used to indicate key odorants
• Only useful for compounds of known identity
• Must have accurate concentration and odor threshold data
• number of odorants detected and the their perceived intensities depend on arbitrarily selected parameters: sample size, isolation method, degree of concentration of aroma extract, etc.
key odorants identified and
accurately quantified, and an
appropriate matrix is available.
Dose response studies
- Sensory evaluation of a suitable product matrix that has been spiked with an odorant (or group of odorants) to determine if the addition causes an increase in the intensity of a specific flavor attribute.- Suitable technique to evaluate ‘cause and effect’ relationship between odorant and sensory attribute.
Comparison of aroma model to real product (validation)
- Use of sensory difference test and/or descriptive analysis
Omission (n – 1) studies
Conventional Difference Tests
Terminology (lexicon) should be developed based not only on attributes of product being studied, but also based on attributes of all n-1 combinations (attributes cannot be predicted).
(with sensory descriptive analysis)
Results of gas chromatography-olfactometry (GCO) and Aroma Extract Dilution Analysis (AEDA) indicated
2-isopropyl-3-methoxypyrazine (3-7 ppb) and p-cresol
(200 ppb) to be “most likely” responsible for cowy/barny and earthy/bell pepper flavors, respectively.
Compounds spiked into a bland cheese matrix across concentration found in Farmhouse cheeses.
Evaluation by descriptive sensory panel in a blind study.
Suriyaphan, O.; Drake, M.A.; Chen, X.Q.; Cadwallader, K.R. Characteristic aroma components
of British Farmhouse Cheddar cheese. J. Agric. Food Chem. 2001, 49, 1382-1387.
description -aromatics associated
with barns and stock trailersreference -p-cresol, Band-aid, phenol
Earthy/Bell Pepper (Aroma)
Earthy/Bell Pepper (Flavor)
Free Fatty Acid
Linking aroma analysis results to flavor lexicon terms
Relationship between p-cresol concentration
and “cowy/barny flavor” intensity
threshold = 0.002 ppb (in water)
Relationship between 2-isopropyl-3-methoxypyrazine
concentration and “earthy aroma/ flavor” intensity
earthy/bell pepper flavor
earthy/bell pepper aroma
p-Cresolthreshold = 55 ppb (in water)
(with difference/similarity scaling)
The unambiguous linking of sensory descriptors with causative chemical components permits researchers to precisely relate sensory flavour quality with the chemistry and technology of Cheddar cheese production.
Potential beefy/brothy compounds identified by GCO.
Compounds spiked into a bland cheese matrix across concentration found in beefy/broth cheese.
Evaluation by similarity-to-control and descriptive sensory analysis.
Cadwallader, K.R., Drake, M.A., Carunchia-Whetstine, M.E. and Singh, T.J. 2006. Characterisation of Cheddar cheese flavour by sensory directed instrumental analysis and model studies. In Flavour Science: Recent Trends.Bredie, W.P. and Peterson, M.A. (Eds.), Developments in Food Science 43, Elsevier, New York, pp. 157-160.
(with R-index method)
Four critical steps in omission studies
Example: Evaluation of key odorants of chipotle peppers
Cadwallader, K.R.; Lorjaroenphon, Y.; Kim, H.; Lee, S-Y. Evaluation of key odorants in chipotle pepper by
quantitative analysis, calculation of odor-activity values and omission studies. In Recent Highlights in Flavor
Chemistry & Biology. Proceedings of the 8th Wartburg Symposium. Hofmann, T., Meyerhof, W. and Schieberle, P.
(eds), Deutsche Forschungsanstalt für Lebensmittelchemie, Garching, Germany.
Predominant Odorants in chipotle peppers by GCO*
A total of 41 odorants were detected by GCO (post-peak
intensity scaling, 7 pt scale) of DSE-SAFE aroma extracts from the three dried chipotle pepper samples
16 compounds had high odor intensities 4.0
2- and 3-methylbutanal, 2-ethyl-3,5-dimethylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-(3)-methylbutanoic acid,
-damascenone, guaiacol, o-cresol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, octanoic acid, p-cresol, sotolon, syringol,
coumarin, phenyacetic acid and vanillin
7 additional odorants had odor intensities 3
* Cadwallader, K.R.; Gnadt, T.A.; Jasso, L. Aroma components of chipotle peppers. In Hispanic Foods: Chemistry and Flavor (Tunick, M.H., González de Mejia, E., eds.); American Chemical Society: Washington, D.C., 2006, 57-66
2- and 3-methylbutanoic acid
0.1 M citrate buffer (pH 4.8)
cellulose (Sigma, St. Louis, MO, USA)
natural capsaicin (Aldrich, St. Louis, MO, USA)
722.4 μg/g (dry basis)b
a Based on dietary fiber (2.6), sugars (2.1) and total fat (0.9) in 100 g of jalapeno pepper (wet basis) (NutritionData, 2006). b Based on analysis of capsaicin and dihydrocapsaicin in chipotle pepper using method of Thomas et al. (1998).
Omission studies – some additional considerations
Eliminating successively (n - 1) all possible components of the mixture- may not reveal much because of antagonistic effects
Eliminating groups of compounds of the model- e.g. where each group is composed of odorants with similar odor qualities or same chemical class
earthy(2-ethyl-3,5-dimethylpyrazine and 2-isobutyl-3-methoxypyrazine)
smoky (guaiacol, 4-methylguaiacol, o-cresol, 4-ethylguaiacol, p-cresol,
m-cresol, syringol, coumarin)
sweet aromatics(2,3-butanedione, HDMF, sotolon and vanillin)
floral/fruity(ethyl 2-methylbutanoate, linalool, phenylacetaldehyde,
-damascenone, 2-phenylethanol, phenylacetic acid)
malty (methylpropanal, 2- and 3-methylbutanal)
sour/sweaty(acetic, 2-methylproanoic, butanoic, 2/3-methylbutanoic
and octanoic acids)
* Terms decided upon by descriptive sensory panel
Omission studies – methodology
O’Mahony, M. Understanding discrimination tests: A user friendly treatment of response bias, rating and ranking R-index tests and their relationship to signal detection. J. Sensory Stud. 1992, 7, 1-47.
odorant group omitteda
earthy (10, 11)
smoky (18, 20, 21, 22, 25, 26, 28, 29)
sweet aromatics (4, 23, 27, 32)
floral/fruity (5, 12, 15, 17, 19, 31)
malty (1, 2, 3)
sour/sweaty (9, 13, 14, 16, 24)
green/plant-like (6, 7)
a Numbers in parentheses indicate odorant numbers omitted. Description of each group was
determined by consensus opinion of the trained sensory descriptive panel. b R-index of each
model is calculated by using John Brown computations (O’Mahony, 1992) against control
(complete model) (n=29; female=21 and male=8). *Significantly different from control at α=0.05
(critical value, expressed in percentage; R-Index = 50% for two-tailed test, α=0.05, n=29 is 17.37).
Synergistic effects are mainly observed for subthreshold concentrations,i.e. a decrease in detection threshold occurs1.
But models are build from odorants at suprathreshold concentrations - in this region antagonistic effects seem to be most common2.
In general, human subjects are unable to identify individual odorants whenthe mixture contains greater than four odorants in total3. This helps explain why omission of one or more odorants from a complex odor mixture oftenis not distinguished from the intact (complete) mixture.
Brown, J. Recognition assessed by rating and ranking. Brit. J. Phychol. 1974, 65,
Czerny, M.; Mayer, F.; Grosch, W. Sensory study on the character impact odorantsof roasted arabica coffee. J. Agric. Food Chem. 1999, 47, 695-699.
Drake, M.A.; Miracle, R.E.; Caudle, A.D. ; Cadwallader, K.R. Relating sensory and instrumental analyses. In Sensory-Directed Flavor Analysis. Marsili, R. (Ed.), CRC Press/Taylor & Francis Group, LLC, Boca Raton, FL, 2007, pp. 23-54.
Engel, E.; Nicklaus, S.; Salles, C.; Le Quere, J.-L. Relevance of omission tests todetermine flavour-active compounds in food: application to cheese taste. Food Qual.Pref. 2002, 13, 505-513.
Karagul-Yuceer, Y.; Vlahovich, K.N.; Drake, M.A.; Cadwallader, K.R. Characteristicaroma components of rennet casein. J. Agric. Food Chem. 2003, 51, 6797-6801.