EVALUATION AND APPLICATIONS OF ODOR PROFILING

An odor profiling procedure was developed based on the ASTM odor profiling method. This modified procedure involved using approximately twenty panelists. Panel sessions and data collection were controlled by computer. The results obtained by this panel compared favorably to results obtained by the ASTM panel for which 150 panelists evaluated each compound, indicating that a small panel can be used to produce replicable results. Statistical methods of finding similarities and dissimilarities among compounds using profile data are discussed and compared to results from a multidimensional scaling (MDS) study in which degrees of differences among compounds were judged directly. These results indicate that profile data can be used to define and map the degree of similarity/dissimilarity among compounds, as well as to define the sensory dimensions on which these compounds differ. The use of factor analysis to study the underlying sensory dimensions of the odor space is also discussed. It is hoped that this type of research will lead to a better understanding of the underlying dimensions used to describe odorants.     

MULTIDIMENSIONAL SORTING, SIMILARITY SCALING AND FREE-CHOICE PROFILING OF GRAPE JELLIES

The sensory data from three different methods, multidimensional sorting, similarity scaling, and free-choice profiling were compared using ten commercial grape jellies as a model system. Without any prior training, the overall similarities/dissimilarities between stimuli were judged using both multidimensional sorting and pair-wise scaling and the sensory attributes were rated using free-choice profiling by different panels. A two-dimensional stimulus configuration best represented the data from each of the three methods. The underlying dimensions of stimulus space were identified from free-choice profiling data and also explained some background variables. The texture, sweetness, sourness, grape flavor and color contributed to both dimensions. All three methods were very similar in describing the most important differences among stimuli as suggested by the highly significant correlation between their first dimensions. The Procrustes analysis coupled with permutation tests, as well as RV coefficient, indicated that similarity scaling and free-choice profiling reached maximum consensus, whereas multidimensional sorting shared slightly lesser consensus with the other two methods.     

Perceptual blending in odor mixtures depends on the nature of odorants and human olfactory expertise

Our olfactory system is confronted with complex mixtures of odorants, often recognized as single entities due to odor blending (e.g., coffee). In contrast, we are also able to discriminate odors from complex mixtures (e.g., off-odors). Therefore, the olfactory system is able to engage either configural or elemental processes when confronted with mixtures. However, the rules that govern the involvement of these processes during odor perception remain poorly understood. In our first experiment, we examined whether simple odorant mixtures (binary/ternary) could elicit configural perception. Twenty untrained subjects were asked to evaluate the odor typicality of mixtures and their constituents. The results revealed a significant increase in odor typicality in some but not all mixtures as compared with the single components, which suggest that perceptual odor blending can occur only in specific mixtures (configural processing). In our second experiment, we tested the hypothesis that general olfactory expertise can improve elemental perception of mixtures. Thirty-two trained subjects evaluated the odor typicality of the stimuli presented during the first experiment, and their responses were compared with those obtained from the untrained panelists. The results support the idea that general training with odors increases the elemental perception of binary and ternary blending mixtures.     

The microencapsulation of odorants as a method of stimulus control and delivery in studies of odor quality perception

The judgment of odor similarity between members of pairs ispreferable to odor naming in some situations. Similarity judgmentsare numerically summarized by multidimensional scaling (MDS)methods, which encourage the use of large numbers of pairs ofodorants; but the presentation of many different odorants involvesdifficulties in stimulus preparation and presentation. The microencapsulationof odorants provides a stimulus presentation method for olfactorytests using nothing more than paper and pencil. This reportexamines the feasibility of the microencapsulated odorant asa stimulus procedure in MDS analyzed similarity judgments. Inaddition, the effects of repeated testing, both within and betweentest sessions was examined. Special attention was given to asymmetryof similarity perception. The new method of odor delivery provedto be excellent, and the MDS model produced was as expected.Systematic trends to judge pairs as increasingly similar overrepeated judging, both within and between sessions, was observed.There were instances of asymmetry of similarity perception betweenthe two orders of presentations of some odor pairs, but notothers. The results suggested additional studies which willlead to a psychometrics of individual differences in odor qualityperception.     

UNDERSTANDING MOUTHFEEL ATTRIBUTES: A MULTIDIMENSIONAL SCALING APPROACH

Multidimensional scaling (MDS) was used to study qualitative relationships among mouthfeel attributes encountered in oral healthcare products. Similarity estimates were obtained from a rapid sorting task and from pairwise similarity ratings. Configurations were interpreted as suggesting four groupings of oral sensations: numbing, astringency, pain and taste. The pain-associated sensations were further differentiated into thermally related sensations and chemically related sensations in some configurations. Two-dimensional solutions from the sorting task and from group-averaged similarity ratings were similar. Individual differences scaling solutions, however, showed unacceptably high stress in two dimensions, suggesting additional nuances in meaning to individual panelists that were not captured by group-averaged data or by sorting data.     

DETERMINATION OF SENSORY OIL-WATER PARTITION COEFFICIENTS OF SINGLE AROMA COMPOUNDS COMBINING PANELIST FREE INTENSITY RATING AND THEORETICAL MODELING OF ODOR INTENSITY

Using an intensity rating with no external calibration, experiments were designed to measure the sensory oil-water partition coefficients of four aroma molecules (benzaldehyde, ethyl butyrate, linalool and acetophenone) as the ratios of concentration producing stimuli of equivalent intensities. Flavored water and oil phases were successively assessed for odor intensity by 24 panelists who were given total freedom regarding scaling strategy. Each session combined five concentration levels of three out of the four studied aromas in a solvent (water or oil). A predominant concentration effect was found for each aroma in both solvents and concentration dependencies of perceived intensity above water and oil were similar. Experimental data were modeled with Fechner, Stevens and Hill equations. Combining results above water and oil solutions to feed a common model led to the evaluation of an overall sensory oil-water partition coefficient for each aroma compound. All three models produced similar partition coefficient values for each aroma that were lower than the related instrumental partition coefficients. Biases previously detected when external calibration had been used were reduced in a large proportion while suggested enhancement of odor intensity by water vapor could not be excluded.     

Analysis of Odor Discrimination by Multidimensional Scaling at Different Temperatures

Discrimination of odorants by the turtle olfactory bulb at 25°and 37°C was examined by the cross-adaptation techniqueand analysed by multidimensional scaling. Analysis by multidimensionalscaling suggests that at 25°C odorants are grouped accordingto their odor qualities in the turtle olfactory system. At 37°C,the cluster formation of odorants, which have a similar odorquality, such as minty and floral alcohol odorants and molecularstructure, in the plot of multidimensional scaling was poor,indicating that the ability of odor grouping according to theirodor qualities was low at 37°C. Chem. Senses 20: 565–571,1995.     

Odor Perception and Beliefs about Risk

Although the perceptual response to environmental odors canbe quite variable, such variation has often been attributedto differences in individual sensitivity. An information-processinganalysis of odor perception, however, treats both the receptionand the subsequent evaluation of odor information as determinantsof the perceptual response. Two experiments investigated whethera factor that influenced the evaluation stage affected the judgementof odor quality and the degree of adaptation to the odor. Peoplewere surveyed in order to measure their tacit perceptions ofthe healthfulness or hazardousness of nine common olfactorystimuli, and the instructional context influenced quality perception.In a second experiment subjects were exposed to an ambient odorunder one of three different conditions, and odorant characterizationinfluenced the degree of adaptation to the odor. Subjects whowere led to believe the odor was a natural, healthy extractshowed adaptation; those told that the odor was potentiallyhazardous showed apparent sensitization; while those told thatthe odor was a common olfactory test odorant showed a mixedpattern: some exhibited adaptation, whereas others showed sensitization.However, detection thresholds obtained before and after exposureshowed adaptation effects that are characteristic of continuousexposure. These findings raise the possibility that cognitivefactors may be modulating the overall sensory perception ofodor exposure (i) for some individuals who exhibit extreme sensitivityto odors and (ii) in situations where adaptation to environmentalodors is expected but does not occur. Chem. Senses 21: 447–458,1996.     

A COMPARISON OF METHODOLOGY APPLIED TO THE SELECTION OF A PANEL FOR SENSORY EVALUATION OF INSTANT COFFEE

Twenty judges performed a variety of chemosensory tasks in order to select the best scores to form a panel for coffee evaluation. An average of correct responses (P%), one-way analysis of variance (ANOVA) and principal components analysis (PCA) were compared. The tests involved: ability to recognize the four basic tastes, identification and matching of odors, taste intensity evaluation and perception of small differences in taste. P% accounted for 71.17 ± 4.34% and 10 of the judges had scores greater than the final average. ANOVA and PCA resulted in 2 different panels consisting of 9 and 12 judges, respectively. The panel was composed by the nine panelists selected by the three methods. The other three panelists that were doubtful could improve to the point of acceptance with additional training. These methods should be used simultaneously to have more security in the acceptance or rejection of panelists.     

Selection of odorants for memory tests on the basis of familiarity,perceived complexity,pleasantness, similarity and identification

In a procedure for the selection of two equivalent sets of familiar and two equivalent sets of unfamiliar odours for use in odour memory studies, 24 na?ve subjects were first asked to rate the familiarity, perceived complexity and pleasantness of 54 a priori unfamiliar odours and 57 a priori familiar odours and to identify the latter. After selection of the 40 most familiar and the 40 least familiar odours, the subjects sorted each of these two sets into groups of similar odours. Their results were analysed by multidimensional scaling and cluster analysis and each set was divided into two recognition sets that had the same degree of similarity between target and distractor odours and that had similar values of familiarity, pleasantness, perceived complexity (familiar and unfamiliar sets) and identifiability (familiar sets). Finally, recognition tasks were performed in order to check the equivalence in memory performance of both the two familiar and the two unfamiliar recognition sets.     

The effect of motor activity on the formation and maintenance of the function of time perception in the course of ontogeny

The effect of motor activity on the perception of the duration of time intervals was studied. Seven hundred and ninety-two subjects aged 7–91 years subjectively measured (scaled) time intervals in the range from 1 to 10 s by methods of estimating, production, and cross-modality matching. The accuracy of scaling was estimated from the value of the relative error. The degree of correspondence of subjective time scales to physical ones was determined from the exponent of the psychophysical scaling function. It was shown that the use of methods with a distinct motor component (production) ensures the smallest error of subjective measurement and the formation of the most adequate subjective time scales. It was found that, for subjects of older age groups, motor activity is a factor that promotes the maintenance of the time perception function.     

CLASSIFICATION OF CHEESES ACCORDING TO THEIR CLOSENESS TO THE CHEDDAR CHEESE CONCEPT1

An important issue in consumer oriented studies is to measure how closely a specific product or perception matches the representation people have of it. We used a concept matching technique to assess the degree to which a variety of different cheeses matched subjects’ concepts of Cheddar cheese. Eighteen subjects made their judgments using their own past experiences with Cheddar cheeses. They made judgments in three separate conditions: only the odor, only the taste and texture and normal eating. This technique provided valid and reliable information on the extent to which the cheeses matched the subjects’ concept of Cheddar cheese. Agreement between classifications of cheeses based on taste and texture only and based on normal eating was high (R=0.90). Agreement between classifications based only on odor and those based on normal eating was weaker (R-0.59). Thus, the taste and texture of the cheeses were more useful than the odor for classifying cheeses as Cheddar.