Differentiation of lemon essential oil based on volatile and non-volatile fractions with various analytical techniques: a metabolomic approach.

Due to the importance of citrus lemon oil for the industry, fast and reliable analytical methods that allow the authentication and/or classification of such oil, using the origin of production or extraction process, are necessary. To evaluate the potential of volatile and non-volatile fractions for classification purposes, volatile compounds of cold-pressed lemon oils were analyzed, using GC-FID/MS and FT-MIR, while the non-volatile residues were studied, using FT-MIR, (1)H-NMR and UHPLC-TOF-MS. 64 Lemon oil samples from Argentina, Spain and Italy were considered. Unsupervised and supervised multivariate analyses were sequentially performed on various data blocks obtained by the above techniques. Successful data treatments led to statistically significant models that discriminated and classified cold-pressed lemon oils according to their geographic origin, as well as their production processes. Studying the loadings allowed highlighting of important classes of discriminant variables that corresponded to putative or identified chemical functions and compounds.

Qualitative and quantitative analysis of volatile constituents from latrines.

More than 2.5 billion people defecate in the open. The increased commitment of private and public organizations to improving this situation is driving the research and development of new technologies for toilets and latrines. Although key technical aspects are considered by researchers when designing new technologies for developing countries, the basic aspect of offending malodors from human waste is often neglected. With the objective of contributing to technical solutions that are acceptable to global consumers, we investigated the chemical composition of latrine malodors sampled in Africa and India. Field latrines in four countries were evaluated olfactively and the odors qualitatively and quantitatively characterized with three analytical techniques. Sulfur compounds including H2S, methyl mercaptan, and dimethyl-mono-(di;tri) sulfide are important in sewage-like odors of pit latrines under anaerobic conditions. Under aerobic conditions, in Nairobi for example, paracresol and indole reached concentrations of 89 and 65 µg/g, respectively, which, along with short chain fatty acids such as butyric acid (13 mg/g) explained the strong rancid, manure and farm yard odor. This work represents the first qualitative and quantitative study of volatile compounds sampled from seven pit latrines in a variety of geographic, technical, and economic contexts in addition to three single stools from India and a pit latrine model system.

Affective dimensions of odor perception: a comparison between Swiss, British, and Singaporean populations.

Do affective responses to odors vary as a function of culture? To address this question, we developed two self-report scales in the United Kingdom (Liverpool: LEOS) and in Singapore (city of Singapore: SEOS), following the same procedure as used in the past to develop the Geneva Emotion and Odor Scale (GEOS: Chrea, Grandjean, Delplanque et al., 2009). The final scales were obtained by a three-step reduction of an initial pool of 480 affective terms, retaining only the most relevant terms to describe odor-related subjective affective states and comprised of six (GEOS) or seven affective dimensions (LEOS and SEOS). These included dimensions that were common to the three cultures (Disgust, Happiness Well-being, Sensuality Desire, and Energy), common to the two European samples (Soothing Peacefulness), and dimensions that were culture specific (Sensory Pleasure in Geneva; Nostalgia and Hunger Thirst in Liverpool; Intellectual Stimulation, Spirituality, and Negative Feelings in Singapore). A comparative approach showed that the dimensional organization of odor-related affective terms in a given culture better explained data variability for that culture than data variability for the other cultures, thus highlighting the importance of culture-specific tools in the investigation of odor-related affect.

Sequential unfolding of novelty and pleasantness appraisals of odors: evidence from facial electromyography and autonomic reactions.

We investigated the effects of odors on appraisal processes and consequent emotional responses. The main goal was to test whether an odor is detected as novel or familiar before it is evaluated as pleasant or unpleasant. Participants performed a recognition task in which they were presented with pairs of unpleasant or pleasant odors (sample and target odors). Within a pair, the sample and target were either identical or different to assess participants' novelty detection; unpleasant and pleasant target odors were contrasted to examine participants' appraisal of intrinsic pleasantness. We measured facial expressions using electromyography and physiological reactions using electrocardiogram and electrodermal activity in response to odors. The earliest effects on facial muscles and heart rate occurred in response to novelty detection. Later effects on facial muscles and heart rate were related to pleasantness evaluation. This study is the first to demonstrate the existence of a sequence of appraisal checks for odors eliciting emotional reaction.

Mapping the semantic space for the subjective experience of emotional responses to odors.

Two studies were conducted to examine the nature of the verbal labels that describe emotional effects elicited by odors. In Study 1, a list of terms selected for their relevance to describe affective feelings induced by odors was assessed while participants were exposed to a set of odorant samples. The data were submitted to a series of exploratory factor analyses to 1) reduce the set of variables to a smaller set of summary scales and 2) get a preliminary sense of the differentiation of affective feelings elicited by odors. The goal of Study 2 was to replicate the findings of Study 1 with a larger sample of odorant samples and participants and to validate the preliminary model obtained in Study 1 by using confirmatory factor analysis. Overall, the findings point to a structure of affective responses to odors that differs from the classical taxonomies of emotion such as posited by discrete or bidimensional emotion theories. These findings suggest that the subjective affective experiences or feelings induced by odors are structured around a small group of dimensions that reflect the role of olfaction in well-being, social interaction, danger prevention, arousal or relaxation sensations, and conscious recollection of emotional memories.

Emotional processing of odors: evidence for a nonlinear relation between pleasantness and familiarity evaluations.

Pleasantness, familiarity, and intensity are 3 interdependent dimensions commonly used to describe the perceived qualities of an odor. In particular, many empirical studies have demonstrated a positive correlation between familiarity and pleasantness. However, on the basis of both theoretical and methodological perspectives, we questioned the validity of such a relation for malodors. We report 2 studies based on subjective judgments of a large sample of odorants (Experiment 1) associated with autonomic recordings (Experiment 2). Multivariate exploratory analysis performed on the data splits the whole odorant set into 2 subsets composed, respectively, of unpleasant and pleasant odorants. Subsequent correlation analyses have shown that the relation between pleasantness and familiarity is specific for the pleasant odors in the 2 experiments. Moreover, autonomic activity was more important in response to malodors than to pleasant odors and was significantly correlated with unpleasantness ratings in the subset of unpleasant odors. These 2 studies argue in favor of a functional dissociation in the relations between both subjective and autonomic responses to odors as a function of pleasantness and indicate that researchers in the olfactory domain should consider the relations between pleasantness and familiarity as more complex than linear.

Selective attention to affective value alters how the brain processes olfactory stimuli.

How does selective attention to affect influence sensory processing? In a functional magnetic resonance imaging investigation, when subjects were instructed to remember and rate the pleasantness of a jasmine odor, activations were greater in the medial orbito-frontal and pregenual cingulate cortex than when subjects were instructed to remember and rate the intensity of the odor. When the subjects were instructed to remember and rate the intensity, activations were greater in the inferior frontal gyrus. These top-down effects occurred not only during odor delivery but started in a preparation period after the instruction before odor delivery, and continued after termination of the odor in a short-term memory period. Thus, depending on the context in which odors are presented and whether affect is relevant, the brain prepares itself, responds to, and remembers an odor differently. These findings show that when attention is paid to affective value, the brain systems engaged to prepare for, represent, and remember a sensory stimulus are different from those engaged when attention is directed to the physical properties of a stimulus such as its intensity. This differential biasing of brain regions engaged in processing a sensory stimulus depending on whether the cognitive demand is for affect-related versus more sensory-related processing may be an important aspect of cognition and attention. This has many implications for understanding the effects not only of olfactory but also of other sensory stimuli.

How pleasant and unpleasant stimuli combine in different brain regions: odor mixtures.

Many affective stimuli are hedonically complex mixtures containing both pleasant and unpleasant components. To investigate whether the brain represents the overall affective value of such complex stimuli, or the affective value of the different components simultaneously, we used functional magnetic resonance imaging to measure brain activations to a pleasant odor (jasmine), an unpleasant odor (indole), and a mixture of the two that was pleasant. In brain regions that represented the pleasantness of the odors such as the medial orbitofrontal cortex (as shown by activations that correlated with the pleasantness ratings), the mixture produced activations of similar magnitude to the pleasant jasmine, but very different from the unpleasant indole. These regions thus emphasize the pleasant aspects of the mixture. In contrast, in regions representing the unpleasantness of odors such as the dorsal anterior cingulate and midorbitofrontal cortex the mixture produced activations that were relatively further from the pleasant component jasmine and closer to the indole. These regions thus emphasize the unpleasant aspects of the mixture. Thus mixtures that are found pleasant can have components that are separately pleasant and unpleasant, and the brain can separately and simultaneously represent the positive and negative hedonic value of a complex affective stimulus that contains both pleasant and unpleasant olfactory components. This type of representation may be important for affective decision making in the brain in that separate representations of different affective components of the same sensory stimulus may provide the inputs for making a decision about whether to choose the stimulus or not.

Cognitive modulation of olfactory processing.

We showed how cognitive, semantic information modulates olfactory representations in the brain by providing a visual word descriptor, "cheddar cheese" or "body odor," during the delivery of a test odor (isovaleric acid with cheddar cheese flavor) and also during the delivery of clean air. Clean air labeled "air" was used as a control. Subjects rated the affective value of the test odor as significantly more unpleasant when labeled "body odor" than when labeled "cheddar cheese." In an event-related fMRI design, we showed that the rostral anterior cingulate cortex (ACC)/medial orbitofrontal cortex (OFC) was significantly more activated by the test stimulus and by clean air when labeled "cheddar cheese" than when labeled "body odor," and the activations were correlated with the pleasantness ratings. This cognitive modulation was also found for the test odor (but not for the clean air) in the amygdala bilaterally.