Prediction models for the pleasantness of binary mixtures in olfaction

Predicting minty compounds binary mixtures' pleasantness by odor intensity in aqueous solutions

The aroma of mint is well-liked by the public, and key flavor odorants in mint aroma had been found, but how these molecules interact and form a satisfying odor remains a challenge. Quality, intensity, and pleasantness are our most basic perceptions of aromas; both intensity and pleasantness can be quantified. However, compared to intensity, research on pleasantness was lacking. Pleasantness was one of the most important indicators for formulating a satisfying mint flavor, and the study of binary mixtures was fundamental to our understanding of more complex mixtures. Therefore, the purpose of this study was to explore the characteristics of pleasantness as a function of concentration and, at the same time, to investigate the relationship between intensity and pleasantness in binary mixtures. Thirty sensory evaluation volunteers participated in the evaluation of the intensity and pleasantness of six key flavor odorants of mint and five binary mixtures. The results showed that the pleasantness increased first and then decreased or stabilized with the rising of concentration; even though the interactions in binary mixtures were not the same, their pleasantness could be predicted using the intensities of the components by Response Surface Design of Experiments, and the goodness of fit was greater than 0.92, indicating that the models had the great predictive ability. PRACTICAL APPLICATION: Whether blending flavors or evaluating them, a great deal of experience is required, yet the acquisition of this experience is a long process. Performing these tasks is difficult for the novice, and it helps to quantify the feeling for the flavor and build some mathematical models.

OWSum: algorithmic odor prediction and insight into structure-odor relationships

We derived and implemented a linear classification algorithm for the prediction of a molecule's odor, called Olfactory Weighted Sum (OWSum). Our approach relies solely on structural patterns of the molecules as features for algorithmic treatment and uses conditional probabilities combined with tf-idf values. In addition to the prediction of molecular odor, OWSum provides insights into properties of the dataset and allows to understand how algorithmic classifications are reached by quantitatively assigning structural patterns to odors. This provides chemists with an intuitive understanding of underlying interactions. To deal with ambiguities of the natural language used to describe odor, we introduced descriptor overlap as a metric for the quantification of semantic overlap between descriptors. Thus, grouping of descriptors and derivation of higher-level descriptors becomes possible. Our approach poses a large leap forward in our capabilities to understand and predict molecular features.

Physiological Effects of a Garden Plant Smellscape from the Perspective of Perceptual Interaction

The purpose of this study was to investigate the physiological recovery effects of olfactory, visual and olfactory-visual stimuli associated with garden plants. In a randomized controlled study design, ninety-five Chinese university students were randomly selected to be exposed to stimulus materials, namely the odor of Osmanthus fragrans and a corresponding panoramic image of a landscape featuring the plant. Physiological indexes were measured by the VISHEEW multiparameter biofeedback instrument and a NeuroSky EEG tester in a virtual simulation laboratory. The results showed the following: (1) In the olfactory stimulation group, from before to during exposure to the stimuli, the subjects' diastolic blood pressure (DBP) (ΔDBP = 4.37 ± 1.69 mmHg, p < 0.05) and pulse pressure (PP) values increased (ΔPP = -4.56 ± 1.24 mmHg, p < 0.05), while their pulse (p) values decreased (ΔP = -2.34 ± 1.16 bmp, p < 0.05) significantly. When compared to the control group, only the amplitudes of α and β brainwaves increased significantly (Δα = 0.37 ± 2.09 µV, Δβ = 0.34 ± 1.01 µV, p < 0.05). (2) In the visual stimulation group, the amplitudes of skin conductance (SC) (ΔSC = 0.19 ± 0.01 µΩ, p < 0.05), α brainwaves (Δα = 6.2 ± 2.26 µV, p < 0.05) and β brainwaves (Δβ = 5.51 ± 1.7 µV, p < 0.05) all increased significantly relative to the control group. (3) In the olfactory-visual stimulus group, DBP (ΔDBP = 3.26 ± 0.45 mmHg, p < 0.05) values increased, and PP values decreased (ΔPP = -3.48 ± 0.33 bmp, p < 0.05) significantly from before to during exposure to the stimuli. The amplitudes of SC (ΔSC = 0.45 ± 0.34 µΩ, p < 0.05), α brainwaves (Δα = 2.28 ± 1.74 µV, p < 0.05) and β brainwaves (Δβ = 1.4 ± 0.52 µV, p < 0.05) all increased significantly relative to the control group. The results of this study show that the interaction of olfactory and visual stimuli associated with a garden plant odor landscape was able to relax and refresh the body to a certain extent, and this physiological health effect was greater with regards to the integrated response of the autonomic nervous system and central nervous system than the effect of only smelling or viewing the stimuli. In the planning and designing of plant smellscapes in garden green space, it should be ensured that plant odors and corresponding landscapes are present at the same time in order to ensure the best health effect.

Odour hedonics and the ubiquitous appeal of vanilla

Our food choices and consumption behaviours are often influenced by odour hedonics, especially in the case of those orthonasally experienced aromas (that is, those odours that are food-related). The origins of odour hedonics remain one of the most intriguing puzzles in olfactory science and, over the years, several fundamentally different accounts have been put forwards to try and explain the varying hedonic responses that people have to a wide range of odorants. Associative learning, innate and molecular accounts of odour pleasantness have all been suggested. Here the origins of the hedonic response to vanilla, which is one of the most liked smells cross-culturally, are explored. The history of vanilla's use in food and medicine is outlined, with a focus on its neurocognitive appeal. While vanilla is one of the most widely liked aromas, it is also rated as smelling sweet to most people. Food scientists are becoming increasingly interested in the possibility that such 'sweet smells' could be used to help maintain the sweetness of commercial food products while, at the same time, reducing the use of calorific sweeteners. Such an approach is likely to be facilitated by the low cost of artificial vanilla flavouring (when compared with the high and fluctuating price of natural vanilla pods).

What Is the Relationship between the Presence of Volatile Organic Compounds in Food and Drink Products and Multisensory Flavour Perception?

This narrative review examines the complex relationship that exists between the presence of specific configurations of volatile organic compounds (VOCs) in food and drink products and multisensory flavour perception. Advances in gas chromatography technology and mass spectrometry data analysis mean that it is easier than ever before to identify the unique chemical profile of a particular food or beverage item. Importantly, however, there is simply no one-to-one mapping between the presence of specific VOCs and the flavours that are perceived by the consumer. While the profile of VOCs in a particular product undoubtedly does tightly constrain the space of possible flavour experiences that a taster is likely to have, the gustatory and trigeminal components (i.e., sapid elements) in foods and beverages can also play a significant role in determining the actual flavour experience. Genetic differences add further variation to the range of multisensory flavour experiences that may be elicited by a given configuration of VOCs, while an individual’s prior tasting history has been shown to determine congruency relations (between olfaction and gustation) that, in turn, modulate the degree of oral referral, and ultimately flavour pleasantness, in the case of familiar foods and beverages.

Pleasantness of Binary Odor Mixtures: Rules and Prediction

Pleasantness is a major dimension of odor percepts. While naturally encountered odors rely on mixtures of odorants, few studies have investigated the rules underlying the perceived pleasantness of odor mixtures. To address this issue, a set of 222 binary mixtures based on a set of 72 odorants were rated by a panel of 30 participants for odor intensity and pleasantness. In most cases, the pleasantness of the binary mixtures was driven by the pleasantness and intensity of its components. Nevertheless, a significant pleasantness partial addition was observed in 6 binary mixtures consisting of 2 components with similar pleasantness ratings. A mathematical model, involving the pleasantness of the components as well as τ-values reflecting components' odor intensity, was applied to predict mixture pleasantness. Using this model, the pleasantness of mixtures including 2 components with contrasted intensity and pleasantness could be efficiently predicted at the panel level (R2 > 0.80, Root Mean Squared Error < 0.67).

Multisensory Flavour Perception: Blending, Mixing, Fusion, and Pairing Within and Between the Senses

This review summarizes the various outcomes that may occur when two or more elements are paired in the context of flavour perception. In the first part, I review the literature concerning what happens when flavours, ingredients, and/or culinary techniques are deliberately combined in a dish, drink, or food product. Sometimes the result is fusion but, if one is not careful, the result can equally well be confusion instead. In fact, blending, mixing, fusion, and flavour pairing all provide relevant examples of how the elements in a carefully-crafted multi-element tasting experience may be combined. While the aim is sometimes to obscure the relative contributions of the various elements to the mix (as in the case of blending), at other times, consumers/tasters are explicitly encouraged to contemplate/perceive the nature of the relationship between the contributing elements instead (e.g., as in the case of flavour pairing). There has been a noticeable surge in both popular and commercial interest in fusion foods and flavour pairing in recent years, and various of the 'rules' that have been put forward to help explain the successful combination of the elements in such food and/or beverage experiences are discussed. In the second part of the review, I examine the pairing of flavour stimuli with music/soundscapes, in the emerging field of 'sonic seasoning'. I suggest that the various perceptual pairing principles/outcomes identified when flavours are paired deliberately can also be meaningfully extended to provide a coherent framework when it comes to categorizing the ways in which what we hear can influence our flavour experiences, both in terms of the sensory-discriminative and hedonic response.

The Rewarding Effect of Pictures with Positive Emotional Connotation upon Perception and Processing of Pleasant Odors-An FMRI Study

This fMRI study was designed to investigate the effect of cross-modal conditioning in 28 female volunteers. Subjects underwent initial fMRI block design scanning during which three pleasant olfactory stimuli were presented and had to be rated with respect to intensity and pleasantness. This was followed by an odor identification task spread out over 3 days: the experimental group was rewarded for successful trials (correct odor identification) with emotionally salient photos, whilst the control group only received randomly displayed, emotionally neutral, pictures. In the final scanning session, the odors were again presented, and subjects rated pleasantness and intensity. Both pleasantness ratings and fMRI data showed effects of the rewarding procedure. Activation in nucleus accumbens and the orbitofrontal cortex confirmed the hypothesis that learnt association of odors with visual stimuli of emotionally positive valence not only increases pleasantness of the olfactory stimuli but is also reflected in the activation of brain structures relevant for hedonic and reward processing. To our knowledge, this is the first paper to report successful cross-modal conditioning of olfactory stimuli with visual clues.

Compound valence is conserved in binary odor mixtures in Drosophila melanogaster

Most naturally occurring olfactory signals do not consist of monomolecular odorants but, rather, are mixtures whose composition and concentration ratios vary. While there is ample evidence for the relevance of complex odor blends in ecological interactions and for interactions of chemicals in both peripheral and central neuronal processing, a fine-scale analysis of rules governing the innate behavioral responses of Drosophila melanogaster towards odor mixtures is lacking. In this study we examine whether the innate valence of odors is conserved in binary odor mixtures. We show that binary mixtures of attractants are more attractive than individual mixture constituents. In contrast, mixing attractants with repellents elicits responses that are lower than the responses towards the corresponding attractants. This decrease in attraction is repellent-specific, independent of the identity of the attractant and more stereotyped across individuals than responses towards the repellent alone. Mixtures of repellents are either less attractive than the individual mixture constituents or these mixtures represent an intermediate. Within the limits of our data set, most mixture responses are quantitatively predictable on the basis of constituent responses. In summary, the valence of binary odor mixtures is predictable on the basis of valences of mixture constituents. Our findings will further our understanding of innate behavior towards ecologically relevant odor blends and will serve as a powerful tool for deciphering the olfactory valence code.

The perception of odor objects in everyday life: a review on the processing of odor mixtures

Smelling monomolecular odors hardly ever occurs in everyday life, and the daily functioning of the sense of smell relies primarily on the processing of complex mixtures of volatiles that are present in the environment (e.g., emanating from food or conspecifics). Such processing allows for the instantaneous recognition and categorization of smells and also for the discrimination of odors among others to extract relevant information and to adapt efficiently in different contexts. The neurophysiological mechanisms underpinning this highly efficient analysis of complex mixtures of odorants is beginning to be unraveled and support the idea that olfaction, as vision and audition, relies on odor-objects encoding. This configural processing of odor mixtures, which is empirically subject to important applications in our societies (e.g., the art of perfumers, flavorists, and wine makers), has been scientifically studied only during the last decades. This processing depends on many individual factors, among which are the developmental stage, lifestyle, physiological and mood state, and cognitive skills; this processing also presents striking similarities between species. The present review gathers the recent findings, as observed in animals, healthy subjects, and/or individuals with affective disorders, supporting the perception of complex odor stimuli as odor objects. It also discusses peripheral to central processing, and cognitive and behavioral significance. Finally, this review highlights that the study of odor mixtures is an original window allowing for the investigation of daily olfaction and emphasizes the need for knowledge about the underlying biological processes, which appear to be crucial for our representation and adaptation to the chemical environment.

The similarity between odors and their binary mixtures in Drosophila

How are odor mixtures perceived? We take a behavioral approach toward this question, using associative odor-recognition experiments in Drosophila. We test how strongly flies avoid a binary mixture after punishment training with one of its constituent elements and how much, in turn, flies avoid an odor element if it had been a component of a previously punished binary mixture. A distinguishing feature of our approach is that we first adjust odors for task-relevant behavioral potency, that is, for equal learnability. Doing so, we find that 1) generalization between mixture and elements is symmetrical and partial, 2) elements are equally similar to all mixtures containing it and that 3) mixtures are equally similar to both their constituent elements. As boundary conditions for the applicability of these rules, we note that first, although variations in learnability are small and remain below statistical cut-off, these variations nevertheless correlate with the elements' perceptual "weight" in the mixture; thus, even small differences in learnability between the elements have the potential to feign mixture asymmetries. Second, the more distant the elements of a mixture are to each other in terms of their physicochemical properties, the more distant the flies regard the elements from the mixture. Thus, titrating for task-relevant behavioral potency and taking into account physicochemical relatedness of odors reveals rules of mixture perception that, maybe surprisingly, appear to be fairly simple.