Springer Handbook of Odor

Plants produce thousands of structurally diverse volatile signal compounds to attract pollinating insects and seed dispersing animals. These compounds are often perceived by humans as a specific fruit or vegetable aroma. Many of these volatiles serve also as defense substances against fungi, bacteria, viruses, and herbivores. The knowledge of precursors and pathways leading to the formation of volatiles in fruits and vegetables has considerably progressed during the last years because of the use of molecular and biochemical techniques. In vitro characterization of the heterologously expressed enzymes has helped clarify the pathways of volatile formation. This chapter will, therefore, provide an overview of biosynthetic sequences and construction mechanisms that are illustrated in most cases using detailed reaction schemes. The various compounds are predominantly ordered according to the biosynthetic pathway that is used in plants to synthesize them and are grouped into carbohydrate-, lipid-, and amino-acid-derived odorants, terpenoids, and glycosidically bound odorants.

The determination of the most important olfactory contributors of a fragrant natural raw material can be an extremely long and complex task which requires the combination of very efficient analytical techniques. Indeed, the characterization of these components is often difficult since the global odor of complex mixtures is not only due to the sum of the olfactory properties of each constituent, but also involves many synergies between each odorant constituents. In addition, the main contributors are often strongly potent odorants contained only in trace amounts, and therefore, their identification requires an exhaustive analysis of the whole mixture. Finally, since the olfactory sense is characterized by strong interindividual differences, a large number of panelists must be involved in such studies in order to bring generalizable data. Consequently, there is still lack of accurate knowledge about the main odoriferous constituents for many natural raw materials, and this situation is paradoxical when it concerns materials widely used for their odorant properties in the flavor and fragrance industry.This chapter presents an overview of the published data about the main odor-active constituents of a selection of natural fragrant raw materials. It describes the chemical structures and olfactory properties of the main odorant components reported in the literature for 10 extracts and essential oils, after a brief description of the general analytical and sensorial issues concerning the determination of key odorants in a mixture.

Incense burning is probably the oldest perfuming method known to mankind. This chapter presents an overview of incense materials from different cultures and times, such as frankincense, myrrh, agarwood, palo santo, copal, and many more. Their botanical sources are given, and their chemical composition and odor properties are discussed. The methods of producing incense preparations are also briefly summarized. Incense use may pose certain health risks in the case of prolonged or repeated exposure, but may also have potential in medical applications. Incense use represents a special challenge to aroma research, as odorants can be newly formed during the process of burning.

This chapter focusses on the formation of flavor active structures by mechanisms based on the degradation of reducing carbohydrates in the presence of amines. As model reactions have led to the elucidation of a confusing diversity of compounds, special attention is given to the understanding of the basic reaction pathways explaining the evolution of the most abundant odorants predominately shaping the aroma profile of most foods.

Coffee is a relatively young beverage that has only been known about since the 17th century. Initially consumed by the aristocracy, coffee has developed since the early 20th century into one of the world’s most popular beverages and is now part of our daily routine and lifestyle. It also represents a major source of income for many coffee-producing countries and is a significant business sector in consumer countries. The triumph of this beverage may have been driven by various factors, but there is no doubt that its unique flavor is the prime reason for its amazing success. Here we will review current knowledge on the aroma of coffee from a chemical and analytical perspective and outline future trends. It is believed that most coffee aroma compounds have already been identified and quantified. Yet little is understood about how these aroma compounds are generated from green coffee precursors during roasting. A true definition of the aroma of freshly roasted and/or brewed coffee is very elusive and some aroma compounds start to degrade the moment they form. Furthermore, research on interindividual differences in the sensation and perception of coffee aromas is still in its infancy. After reviewing our current knowledge on coffee aroma compounds, we will outline recent developments in time-resolved analysis in three fields:1.Aroma formation during roasting2.Aroma extraction during espresso preparation and3.In-mouth release during consumption.Finally, we will address predictive models for sensory profiles derived from instrumental measurements – possibly the holy grail of aroma sciences.

This chapter presents some background information on the aroma-active volatiles in beer. It explains the evolution of the flavor-active compounds that are derived from the raw materials, namely water, malt, hops, yeast, and adjuncts. Especially the utilization of hops as well as hop itself as a key ingredient for the production of beer will be discussed. Furthermore, the flavor changes that occur during the most important manufacturing steps are summarized. Additionally, selected volatiles causing desired flavors as well as volatiles responsible for undesired off-flavors will be highlighted. Finally, this chapter will provide a detailed view on the impact of beer lagering and aging on the volatile profile of aroma-active compounds in beer.

Wine aroma is related to human cognition through multimodal stimuli, particularly in the case of volatile compounds detected by orthonasal and retronasal perception. In fine wines, aroma may be associated with associations of complexity, finesse, and elegance, sometimes attaining the level of uniqueness that makes them a source of a great pleasure. This chapter reviews the diversity of volatile components constituting wine aroma, including compounds originating from grapes, the metabolism of wine microorganisms during alcoholic and malolactic fermentations, implicating Saccharomyces cerevisiae and Oenococcus oeni, respectively, and oak barrels during wine aging. It will also address those associated with off-odors. The impact of all these compounds on wine aroma and quality is considered, including recently described perceptual interaction phenomena (i. e., masking, synergistic effects, and perceptual blend-ing) and the influence of nonvolatile compounds in the wine matrix on aroma perception.

In a botanical sense, fruits are the developed part of the seed-containing ovary. Evolutionarily speaking, plants have developed fruits presumably to attract insects, birds, reptiles, and mammals and hence to spread the seeds. Fruits can be dry such as the pod of a pea, or fleshy such as a peach. As humans, we enjoy fleshy fruits for their flavor and nutritional value. In this chapter, we will review the common volatiles that are produced by the major fruits with commercial value: tomato, citrus, apples, and strawberries. Some volatile compounds are commonly produced by all crops, simply by the fact of common biosynthetic pathways, while other compounds are specific to certain fruit species. Fruit-specific aroma depends on species, cultivar, growing conditions, and developmental and maturity stage. In the end, however, what gives a fruit its specific flavor is the combination of volatile and nonvolatile compounds, including sugars, acids, and other water-soluble and insoluble compounds.

The delicious aroma of freshly cooked meat is highly attractive, stimulating the gastric juices, and giving us early indications that the meat and its eating experience are likely to be enjoyable. Consequently, there is much interest from the food industry in understanding how to control and optimize meat aroma. The aroma profiles of cooked and cured meats are extremely complex, comprising several thousand volatile compounds, of which only a few impart characteristic meaty notes. This chapter covers the characterization of meat aroma, identifying those compounds that impart meaty aromas and those that give species character, as well as those which generate off-notes. The formation pathways of these compounds are reviewed, and the role of pre- and post-slaughter conditions in altering the aroma profile of the meat is discussed. Production of optimum meat flavor involves careful selection of diet and breed, good control over pre- and post-slaughter conditions, and choice of appropriate processing conditions to maximize the formation of taste and aroma compounds.

Foods that contain fat are generally well liked by consumers. Fats and oils contain a large variety of aroma compounds. These aroma compounds are either trapped within the oil phase of the food matrix or can be formed from the lipids themselves. The analysis of aroma compounds in fat is difficult. This chapter discusses the analytical techniques used to identify the lipid-associated odorants and presents some comparisons of the results obtained from these techniques. Insights into the main families of chemicals imparting specific flavors to fat-containing foods and their formation pathways are presented, with a special emphasis on the compounds that are formed from lipids. Based on this premise, the aroma compositions of selected vegetable oils and animal fats are reviewed with a focus on the specific compounds that have been discovered during the last decade and their proven or postulated formation pathway. Finally, odor descriptions of many of the main compounds and their relative contribution to the overall flavor of fats and oils are given.

The area of protecting and delivering aroma compounds in a food application is most challenging. At this time, well over 8000 aroma compounds have been found in nature and they vary widely in physical and chemical properties which makes their protection and delivery very problematic (evaporation and chemical reactivity). Thus, one attempts to design encapsulation systems that protect the key aroma compounds but yet deliver them when needed using cost-effective and legally approved materials and methodologies. This chapter provides strategies used to accomplish these goals. Overviews of materials and methods used in encapsulation and controlled delivery are presented. The final section offers insights into unmet needs in this area.

The perception of flavor is induced by the release of aroma compounds in the vapor phase. The olfactory perception is not only related to the nature of aroma compounds initially present in the food, but also to their distribution between the different phases. After a description of the interactions established between the aroma compounds and different constituents of food, this chapter looks at physico-chemical characteristics of aroma compounds and at the composition and properties of food matrices. Then, in order to understand the behavior of aroma compounds in the matrices, study methods of interactions are described. The assessment of the release is done by determining the partition coefficients and mass transfer between phases. The conclusion opens the way on the preservation of aroma compounds.

In this chapter, we will briefly describe the complexity of the main mechanical, biochemical and physicochemical phenomena that occur in the mouth during food consumption using examples. To better understand the reactions occurring in the mouth during food consumption, in vitro systems called model mouths were developed to simulate food consumption and thus answer some of the more fundamental questions regarding olfactory perception. This chapter provides examples of the applications of the model mouth in performing oral functions, such as mastication, saliva production and airflow, as well as swallowing, while the released volatile compounds are measured. The recent model mouth designs represent the actual occurrence of food consumption under oral conditions in a more accurate way. We believe that this type of methodology will be even more commonly applied in the future to improve the knowledge in this field.

This chapter serves as an example of governmental regulatory oversight and safety assessment of flavorings. In the European Union (EU), the regulatory framework for the use of flavoringsflavoring in and on foods is provided by Regulation (EC) No 1334/2008. The Regulation provides for three basic regulatory tools: (i) a Union list of flavorings and source materials approved for use in and on foods, (ii) conditions of use of flavorings and food ingredients with flavoring properties in and on foods, and (iii) rules on the labeling of flavorings. The safety evaluation of flavoringflavoringsafety evaluation substances has been performed using a group-based approach. The procedure is based on a decision tree that considers information on structure–activity relationships, metabolism, intake, and toxicity.

Packaging materials based on paper are often used for packing foods, for example, flour, spices, rice, noodles and frozen products. Like all materials used for packing, cardboards and papers have to fulfill legal requirements in order to avoid the transfer of undesirable and harmful packaging constituents to foods. These legislations also cover the deterioration in the organoleptic properties of the packed food. Thus, methods and standards have been established in order to evaluate the sensory impact of packaging on foods.This chapter reviews several human-sensory tests that are often applied for the evaluation of the organoleptic – in particular olfactory – quality of cardboards and papers. The standards enable a fast and reliable detection and characterization of packaging odors, but sources of odors are difficult to identify. Therefore, instrumental–analytical methods like gas chromatography in combination with mass spectrometry (GC/MS) and/or olfactometry (GC/O) are helpful tools for the identification of undesirable odorants. Based on the chemical structures, pathways and precursors, contamination sources can be detected and strategies for reduction or elimination of packaging odor can be developed.

Precise odorant analysis by gas chromatography (GCgas chromatography (GC)) with olfactometry (Oolfactometry (O)) methods, especially for complex sample mixtures, relies firstly upon achieving the best possible chemical separation of the volatile components. Odorants are often sampled from the headspace into the GC, since this is where our perception of the product is usually conducted, but the total sample or a liquid extract (e. g., from a wine sample) may also be introduced into the GC. Multidimensional GC (MDGCgas chromatography (GC)multidimensional (MDGC)heart-cut) methods achieve higher resolution than single column GC. For complex mixtures heart-cut MDGC, where discrete subsamples of eluate are transferred from the first column separation for analysis on a second column, significantly improve resolution of the components in the heart-cut fraction. Alternatively, comprehensive two-dimensional GC (GC × GC) improves resolution for all components in the injected material, but here the second column must complete analysis of each fraction very quickly e. g., within 5 s. Both approaches have been widely studied for aroma extracts and essential oils. Integrating simultaneous olfactometry – providing sensory assessment of a compound – and mass spectrometry (MSmassspectrometry (MS)) – providing identification of the compound – in the MDGC experiment is important. At the end of the second column, split flow of effluent to O and MS allows effective dual detection of the resolved components. This is best conducted by the heart-cut MDGC approach. Novel methods usually based on MDGC can also be used to re-combine different odor-eliciting compounds, to study synergistic effects.

The nasal olfactory receptors allow us, as human beings, to detect and perceive odors almost instantaneously upon exposure and over a broad range of concentrations down to ultratrace levels. Translating this rapid and sensitive detection of odorant molecules to the analytical laboratory is a challenging, nontrivial endeavor that remains unachieved to date. On-line mass spectrometry based on chemical ionization (CIMS) comprises sophisticated analytical techniques that meet several of the key requirements in odorant detection, namely fast response times and direct analyses, trace level limits of detection, and a high sensitivity to a suite of odors or, more specifically, odorants. This chapter discusses on-line CIMS and its application in odorant detection in selected fields. The prominent CIMS techniques of selected ion flow tube mass spectrometry (SIFTselected ionflow tube (SIFT)-MSmassspectrometry (MS)), proton transfer reaction MS (PTRprotontransfer reaction (PTR)-MSmassspectrometry (MS)) and atmospheric pressure chemical ionization MS (APCI-MS) are considered, commencing with a brief introduction to their historical developments and a discussion of their operational features and suitability for odorant detection, followed by a review of their widespread applications in odorant measurements in diverse fields of study.

This chapter concerns enantioselective gas-chromatography (Es-GCenantioselective gas chromatography (Es-GC)) with cyclodextrin derivatives as chiral stationary phases for chiral recognition of volatile odorants in the flavor and fragrance field. The text is divided into two main parts. The first one is more general and deals with enantiomers and odor and need for chiral recognition, evolution of chiral stationary phases for Es-GC since its beginning, followed by the history of cyclodextrins and their applications to enantioselective GCgas chromatography (GC). It also includes some theoretical aspects of enantiomer separation with cyclodextrin derivatives and their influence on routine chiral recognition.The second part concerns the strategy of chiral recognition in routine analysis with cyclodextrin derivatives as chiral stationary phases illustrated by examples with real natural product samples. This part describes enantiomer automatic identification or their excess or ratio determination in complex mixtures by enantioselective GC combined with mass spectrometry; in particular it deals with the potential of multidimensional techniques and of fast GC in chiral recognition and the role played by mass spectrometry. The last paragraph concerns the use of total analysis systems in chiral recognition.

This chapter summarizes terms, definitions, and reference materials used for stable isotope ratio analysis (SIRAstable isotoperatio analysis (SIRA)) of the bioelements hydrogen, carbon, and oxygen. The principles of biotic and abiotic fractionation in biomolecules like flavor compounds are explained. A short review of the common methods for the determination of isotope ratios $$\mathrm{{}^{2}H/^{1}H}$$2H/1H, $$\mathrm{{}^{13}C/^{12}C}$$13C/12C, and $$\mathrm{{}^{18}O/^{16}O}$$18O/16O, using isotope ratio mass spectrometry (IRMSisotope ratio mass spectrometry (IRMS)) and nuclear magnetic resonance spectrometry (NMRnuclear magnetic resonance (NMR)) of hydrogen and carbon ($$\mathrm{{}^{2}H}$$2H- and $$\mathrm{{}^{13}C}$$13C-NMR) are introduced. Further the focus is set on selected applications of authentication control of flavor compound and flavorings using isotope ratio analysis. Examples of benzaldehyde, vanillin, vanilla flavorings and vanilla extracts, butanoic acid, isoprenoids, and essential oils as well as fruity flavor compounds like γ- and δ-lactones are presented. Potentials and limitations of SIRA are discussed taking the analytical requirements into consideration, as well as representative databases and suitable guidelines for authenticity assessment.

It has been a longstanding goal of many research groups to replicate human olfactory sense with instruments. Sensor technology aims not only to replace the traditional analytic methods that are mostly focused on individual chemical identification and quantitation, but also to predict the human perceptions of smell, odor recognition and odor hedonics, thus replacing human sensory evaluation. Sensors have progressed from early gas sensors, to e-noses and e-tongues to biosensors and bio-e-noses that utilize elements from natural signal transduction to gain better sensitivity and selectivity. There has recently been a rapid increase in research and development of advanced sensor technologies and enabling technologies such as nanotechnology, cellular biology, wireless communication, and neural computing methods that have helped overcome the sensitivity, selectivity, portability and recognition problems of early sensor systems. Much of this development comes in response to global bioterrorism and other security threats. The activities in the various areas enabled by machine olfaction are poised to impact many industries not only as potential enablers of competitive advantage, but also through international standards development and enforcement. However, while machine olfaction instruments and sensors systems have been under development for more than 30 years, they still cannot completely replace the human senses for sensitivity, selectivity, and speed. While complete replacement of human sensory perception is not yet possible, certain sensor arrays provide fast, cheap, portable, networkable, low-expertise alternatives in some applications where simple detection is required. Nevertheless, current machine olfaction devices can provide a low-sample preparation approach that significantly reduces the amount of human sensory and advanced chemical testing needed.

The recent technical advances in functional expression of olfactory receptors (ORolfactory receptor (OR)odorblockerenhancerchemoreceptors) make full deorphanization of human OR repertoire a realistic objective. Such a global knowledge of the precise mechanisms of odorant/receptor pairings will represent a crucial step for the development of an accurate model of how human nose perceives its chemical environment. Beyond its interest for basic science, it will also lead to the development of industrial applications such as receptor-based odorant design, development of selective odor blockers or enhancers and represents therefore an interesting opportunity for players active in the field of flavors and fragrances. Here, we will describe and discuss a high-throughput screening approach that aims at the objective of human OR mass deorphanization. However, the completion of this ambitious task is not a prerequisite to the development of commercial applications. With the expanding number of deorphanized ORs, structure–activity relationship studies on OR responding to an odorant of interest has already started. Likewise, the use of the screening approach to identify either blockers for malodor-responding ORs or positive enhancers of fine fragrance-tuned ORs is underway. These different aspects will also be discussed. Finally, beyond the human ORs, other classes of human chemoreceptors for volatiles as well as animal chemoreceptors may also represent industrial opportunities that will be briefly reviewed.

This chapter is an up-to-date review of psychophysical means for testing the human sense of smell. Strengths and weaknesses of major psychophysical paradigms are discussed, including ones associated with the measurement of odor detection, discrimination, identification, memory and both suprathreshold intensity and pleasantness assessment. Factors that influence olfactory test results are discussed in detail, including the influences of test parameters, such as test length, on test reliability. It is pointed out that non-forced-choice tests, unlike forced–choice tests, are incapable of discerning subject biases and malingering. Issues related to the comparison and interpretation of test results from nominally disparate tests that differ in sensitivity, reliability, operational demands, and other factors are discussed.

In 1995 the technical committee TC264 air quality of the European Committee for Standardization convened the working group 2, which developed an odor testing standard. It was released in 2003 as EN 13725 air quality – measurement of odor concentration using dynamic olfactometry. As the methodology of dynamic olfactometry according this European Standard is approved among others in Australia as AS 4323.1 and in Chile as NCh 3190, the EN 13725 today is the most applied standard worldwide.Other used methods for determination of odor thresholds are ASTM 679 as well as Japanese and Chinese standards. Compared with the EN 13725 these standards are working on a lower detail level concerning technical requirements and execution description.In 2012 the TC264 took a resolution to review the standard. A revised draft standard is expected to become available in 2017.The revised standard will contain comprehensive guidance on reference material, measurement uncertainty, health and safety issues, materials for olfactometry, sample storage and the sampling of different odor sources. Once the endpoint of the revision has been reached a release of an ISO standard based on EN 13725 is envisaged.

The field of environment odor assessmentodorassessment involves evaluating odors in ambient airambientair, focussing primarily on offensive odors. Olfactometryolfactometry (O) is an indispensable tool used in this field to assess odors and establish their concentration at the source. This area of application incorporates regulated methods for sampling and measurement, and includes field inspections that aim to evaluate odors at or in close proximity to the problematic neighborhood. The human sense of smell is the primary tool for such analyses, representing an ideal proxy for the local population affected by the offending odor.

Indoor air is a complex and dynamic mixture of a huge variety of volatiles and particulate matter. Some of the constituents are odorous and originate from various sources such as construction materials, furniture, cleaning products, inhabitants and many more. Therefore, every indoor environment has a unique chemical composition in its air space. Volatile organic compounds and odorants in indoor air may cause psychological and/or physiological discomfort in humans. To reduce unwanted indoor air pollutants, it is of great interest to evaluate their sources and chemical structures. This chapter will provide an overview of methods used to evaluate indoor air and material emissions as well as current knowledge of odorants emitted by selected and common sources of indoor odors and in addition human bio-effluents. Measures to avoid and reduce odors as well as health concerns associated with indoor odorants will be discussed. Importantly, this chapter focuses on odorous organic volatiles present in indoor environments – non-odorous volatile organic compounds that can also affect indoor air quality will be mentioned only in passing.

Chemosensory perception is one of the most important systems for appraisal of the environment. In contrast to physical sensory modalities, whose stimuli nature is constant (light, sound), the ever-changing odorous environment requires that the chemosensory system can cope with varying situations. This is accomplished by a large number of odorant receptors, most of them with a broad recognition spectrum due to a plasticity of the binding cavity. This apparent fuzziness is mandatory for the combinatorial mode of odorant recognition that allows reception of an almost infinite number of odorants with an enormous discriminatory power. Odorant receptors are expressed in olfactory sensory neurons (OSNolfactory sensory neuron (OSN)s) following the one-neuron one-receptor rule; only one from more than a thousand receptor genes is expressed, in fact either from the maternal or the paternal allele. Thus, the receptor type determines the molecular receptive range of a particular chemosensory neuron. The choice and continuous expression of a particular receptor gene is supposed to result from a hierarchy of regulatory processes, involving cis-regulatory deoxyribonucleic acid (DNAdeoxyribonucleic acid (DNA)) elements, epigenetics and a negative feedback mechanism mediated by the receptor protein itself. The chemoelectrical transduction process in OSNs is mediated by an intracellular reaction cascade leading to the generation of action potentials that are conveyed to the brain. An individual OSN extends its axon directly into the olfactory bulb where it targets onto a distinct spherical neuropil – the olfactory glomerulus – that connects sensory input with output neurons and local modulatory interneurons. The connectivity is remarkably precise such that only axons from neurons with the same receptor type innervate a specific glomerulus. The molecular determinants that control the complex process of axonal pathfinding, segregation, and targeting that lead to a receptor-specific wiring of the olfactory system have been only partially unraveled.

There are myriads of odorous molecules that we perceive and it is remarkable that most of us seem to have very similar odor impressions that originate from a specific stimulus and the sense of smell appears to be robust during much of a lifetime. When perceiving scents, olfactory receptor (ORolfactory receptor (OR)olfactorycortexolfactorymucosaperireceptor event) proteins are at work to translate chemical information into neuronal signals that are decoded in the olfactory cortex to provide us with an odor image. Proposed in the middle of the last century but only substantiated with intriguing laboratory data during the last decade, there are enzymes expressed at high levels in the olfactory mucosa, and they metabolize xenobiotics including odorants and produce many new chemical species. Examples demonstrate that such perireceptor events can alter the receptor-dependent activation pattern in the olfactory neuroepithelium, which has an impact on the quality and the intensity of odor stimuli. Results that do not seem to fit a model or a hypothesis may make sense if perireceptor events are brought into the equation.

This chapter outlines the metabolism of important food odorantsfoododorant and its impact on their bioactivity. The first section describes general metabolic pathways including functionalization (phase 1), conjugation (phase 2) and export (phase 3). These pathways are intended to excrete the compounds, which can be regarded as xenobiotics. In the second section, the metabolism of important classes of odorants, that is, alcohols and aldehydes, esters, thiols, terpenes, and phenylpropanoids is presented in detail. Among the terpenes, the focus lies on the monocyclic monoterpene hydrocarbon carvone, the monocyclic monoterpene ketone pulegone, the bicyclic monoterpene oxide 1,8-cineole, the bicyclic monoterpene ketone thujone, and on the allylalkoxybenzenes estragole and methyleugenol and coumarin among the phenylpropanoids. Recent studies are presented and each pathway is depicted in a separate reaction scheme. The contribution of each path either to detoxification or to toxification is discussed. The last section finally deals with conclusions and an outlook for further research.

A plethora of structurally diverse environmental chemosignals convey critical information for survival, health, and reproduction. To meet the bewildering structural complexity of the chemical odor space, distinct cellular mechanisms and, ultimately, sensory subsystems have evolved to detect and discriminate these varied chemostimuli. Mammalian olfactory subsystems can be categorized by the stimuli they detect, the signaling proteins they express, and the central circuits that process these information. This chapter is centered on noncanonical olfactory subsystems and their peripheral sensory structures – the vomeronasal organ, the septal organ of Masera, and the Grüneberg ganglion.

Olfactory loss is frequent. However, in public not many people complain of that, or they are even not (fully) aware of it. This indicates that it is possible to live a life without a sense of smell, albeit it is more dangerous, less pleasant, and food tastes much less interesting. Most common causes for smell loss are sinunasal disease (chronic rhinosinusitis with and without nasal polyps), acute infections of the upper airways, head trauma, and neurodegenerative disorders. In many people smell loss seems to be due to the aging process. Before treatment olfactory disorders are diagnosed according to cause with the medical history being a big portion of the diagnostic process. Olfactory disorders are in principle reversible, with a relatively high degree of spontaneous improvement in olfactory loss following infections of the upper respiratory tract. Medical treatment is according to cause. It also involves surgical approaches as well as conservative treatments including the use of corticosteroids, antibiotics, or smell training. Because today olfactory dysfunction seems to receive more attention than in previous years it can be expected that tomorrow we will have more specific and effective treatment options available.

Humans are traditionally considered to have a poorly developed sense of smell that is clearly inferior to that of nonhuman animals. This view, however, is mainly based on an interpretation of neuroanatomical and recent genetic findings, and not on physiological or behavioral evidence. An increasing number of studies now suggest that the human sense of smell is much better than previously thought and that olfaction plays a significant role in regulating a wide variety of human behaviors. This chapter, therefore, aims at summarizing the current knowledge about human olfactory capabilities and compares them to those of animals.

Olfactory receptors (ORolfactory receptor (OR)s) are not exclusively detectable in the olfactory epithelium but are ectopically expressed in all other body tissues tested so far such as brain, heart, lung, testis, intestine, and skin. Within these tissues, a specific subset of ORs can be found with some of the ORs being exclusively expressed in only one specific nonolfactory tissue and other OR subsets being more widely distributed throughout different tissues of the body. It is assumed that ectopically expressed ORs, which are nothing but highly specific chemosensors, play a role in the regulation of cell–cell recognition, migration, and pathfinding processes. Additionally, they are attributed to have potential as diagnostical and therapeutical tools as ORs are differentially expressed in pathological tissues (e. g., cancer tissue). Besides the canonical signaling pathways of ORs, as found in the olfactory tissue, alternative pathways are activated in the diverse nonolfactory tissues. In this chapter, the expression and function of ORs outside the olfactory epithelium of the nose will be highlighted.

Flavors and odorants are important aspects in our daily life controlling a diversity of selection processes like food intake, social interactions, aversion or love. The detection of flavor and odorant compounds by our sensory organs for taste, olfaction and chemesthesis are important for the detection and discrimination among chemical cues in the environment. Flavors and odorants have impact on food selection as well as social interaction by being influential for feelings of pleasure and discontent, sexuality and mood. Most of flavors and odorants originate from spice plants like capsaicin from chili or vanillin, the odorous principle of vanilla. They activate a large set of receptors and ion channels. In this review, we summarize the recent findings regarding the effects of flavors and odorants on the activity of the transient receptor channel family (TRPtransient receptor potential (TRP)) and their potential role in olfaction, taste and chemesthesis. Potential health benefits of spices are discussed in the light of their bioavailability of the flavors and odorants after systemic intake.

Food-derived odor compounds determine the flavor of foods. However, these volatile compounds are known to elicit biological activities beyond their flavor function. Plants rich in volatile compounds, for example mint, have been used in traditional medicines worldwide to improve wound healing and to treat inflammation-related illnesses. In this chapter, we focus on the anti-inflammatory activity of different plant essential oils and individual odor compounds. Here, it is reviewed that odor compounds possess anti-inflammatory activity in pre- and postabsortive model systems, in vitro, ex vivo, and in vivo. Monocytes, macrophages, and fibroblasts are cells that play an important role in the innate immune response. In vitro models of these cells are commonly used to identify the mechanisms of action of the anti-inflammatory activity of volatile compounds. An inflammatory stimulus initiates the toll-like receptor-mediated signaling pathway, resulting in the gene expression and further the release of cytokines. Thus, an anti-inflammatory effect of odor compounds is measured by a reduction of cytokine messenger ribonucleic acid (mRNAmessenger ribonucleic acid (mRNA)) expression or release from stimulated cells. For example, eucalyptol, borneol, and camphor have been identified as anti-inflammatory active compounds that may be used to prevent or treat inflammation-related diseases.

Manyskinsensitization natural and synthetic odorant materials contain structural features such as aldehyde functionalities or conjugated double bonds which lead to a certain chemical reactivity. Such molecules have the intrinsic ability to modify skin proteins, and if they are applied to skin at too high doses this may trigger an immune reaction leading in sensitive individuals to an allergic reaction. Here we review the underlying molecular mechanisms, the key structural classes of sensitizing odorant molecules, the predictive tests to identify fragrance allergens, the epidemiology of fragrance allergy, and the measures taken to avoid such reactions based on a risk assessment.

Aroma therapy has become a well-established part of complementary and alternative medicine in pediatrics mainly because it is accepted and desired by many parents. However, the scientific base of several of these methods is often contradictory. This chapter provides an overview of data on aroma therapy in neonatologyneonatology and tries to explain its physiological background.

The act of smelling is a fundamental perceptual process mediated by the evolutionary very old olfactory system. Smells influence human behavior strongly related to survival, such as food consumption, hazard avoidance, sexuality, and reproduction. Hence, olfactory stimuli are of high ecological importance and are processed in phylogenetically old brain areas. This anatomical deviation leads to changes in the cortical organization of networks responsible for olfactory processing in comparison to other sensory systems that can be perfectly examined with the help of neuroimaging methods.Within this chapter insights about the anatomy of the peripheral and central olfactory structures will be provided and physiological processes that are the basis for olfactory perception will be explained. The way of the olfactory information processing – starting with the molecules that are sniffed and bind to the receptors in the olfactory epithelium, to information transmission to the olfactory bulb and onward to olfactory cortical areas – will be traced. Alongside this, the reader will be informed about the clinical implications of the sense of smell.

Thisodor valenceperception chapter serves as an introduction to our current understanding of the stimulus-driven and experience-driven mechanisms, which give rise to affective evaluation of odorants. We will start by focusing on the potential evolutionary benefits of rapid elicitation of affective responses to odors and provide an overview of paradigms and approaches that can be used to quantify these experiences in an experimental setting. We will then outline evidence in favor of stimulus-driven and experience- or learning-driven accounts of odor valence perception, representing two prevalent theories. Finally, we provide an overview of the cortical networks that support the assignment of valence to odors.

This chapter advocates for adopting a theoretical and experimental approach that goes beyond the use of valencevalence as the most interesting dimension in emotional reaction to odors.Although valence is a dominant dimension of odor perception, limiting the description of emotional response to positive versus negative (valence) and activating versus calming (arousalarousal) feelings is perhaps oversimplified and not well suited for a comprehensive view of odor-related effects. Just as inappropriate are basic emotionsbasicemotion, usually defined as six states (fear, anger, sadness, surprise, joy or happiness, and disgust) putatively characterized by specific neural, physiological, expressive, and feeling components. Here, we present an appraisalappraisal approach of emotions as a plausible alternative. This kind of approach reconciles a priori incompatible characteristics observed in odor perception like the immutability and the flexibility of chemosensory preferences. After having exemplified this aspect with several studies from the recent literature, we will particularly emphasize feelings. We provide an empirical demonstration that feelings are broader than valence and both stable and variable across cultures. We argue that this approach provides an ecological model of the emotion process where olfactory emotions are understood considering their functional role, which is to adjust or to solve olfactory-linked survival-relevant problems.

The mammalian olfactory system is intertwined with emotional and memory centers of the brain, thus providing an ideal model to study olfactory-based fear conditioning, a behavior lying at the intersection of perception, emotion, and cognition. In the present chapter, we first outline a brief overview of the olfactory system’s anatomy, and then, we define the structural and functional changes induced by aversive olfactory conditioning with a clear focus on rodent and human models. In detail, we discuss aversive experience-dependent modulations at each level of the olfactory pathway, differentiating between experimentally presented (shock) and naturally occurring aversive pairings (toxicosis). Whenever possible, developmental trajectories are reported. The description of aversive olfactory conditioning mechanisms are finally used to provide insights on psychiatric and medical conditions characterized by aversive odor memories which may open up future possibilities of developing novel treatment options.

Even though rarely thought of, all environmental spaces contain odor information. It has been proposed that the preconditions for episodic olfactory memoryepisodicolfactory memory may not be optimal. For example, environmental olfactory information often goes unnoticed and barely evokes attention in humans and semantic activations that are a prerequisite for optimal episodic memory functioning are typically restricted. Still, it is highly likely that olfactory information will become part of a memory representation that is linked to a specific event. This implies that an event-congruent exposure of an odor carries the potential to trigger all, or parts of, a previous episode. Indeed, available evidence shows that odors may serve as powerful reminders of past experiences. This is demonstrated by studies exploring the nature of odor-evoked autobiographical memoriesodor-evoked autobiographical memory and by controlled experimental paradigms where odors have been embedded in a learning context and later reinstated at retrieval where an increased memory recollection for the target information is often observed. These observations converge on the notion that odor memories are retained over long periods oftime.In this chapter, we will highlight olfactory cueing of memory and how odors may act as reminders of the recent and distant past.

This chapter summarizes research on the development of human olfactory skills to rely on different cues conveyed by odorants, such as odor quality, intensity, position in space, novelty/familiarity, and hedonic value. The sensory, neural, and psychological dimensions at the root of these early aptitudes remain poorly explored in humans, but one can safely affirm that any weak odor to which the infant has previously been nonadversely exposed will have a higher reinforcing value than any novel odor. Developmental differences in odor discrimination and appreciation are certainly causally multiple and may depend on general or olfaction-specific cognitive factors which can be traced back to prenatal or neonatal olfactory exposure effects. But some odors may also be unconditionally attractive or aversive from birth due to genetic or epigenetic factors.Increased and systematic research efforts on olfactory development during the neonate, infancy, and childhood periods are important for several basic and applied reasons. First, they can illuminate general issues on the biological, psychological, ecological, and sociological mechanisms underlying human perception. Second, findings suggest that infantile experience with specific odors can canalize lifelong perceptual abilities. These long-term effects of early chemosensory experience relate to notions, such as sensitive periods, cerebral plasticity, and memory, and also to the early programming of food liking, addictive habits, and affiliative choices.

The olfactory sense plays an important role in food and flavor perception, and thus in our eating behavior. This chapter provides an overview of the current status of research in this field. It describes the two-way relation between subdomains of olfactory function (detection sensitivity, pleasantness; ortho- and retronasal odor exposure) and various aspects of eating behavior (appetite, food choice, intake), and discusses the difficulties in this type of research. Findings are summarized which show that metabolic status might affect odor perception and vice versa odor exposure can affect appetite. Determination and anticipation of the type of food by odor cues may tailor the preparation of the body to the specific macronutrient composition of the anticipated foods. However, this does not automatically lead to subsequent specific food intake. Eating behavior is a complex phenomenon that entails more than simple liking or wanting of foods induced by olfactory cues, rendering the need for more research to get a better grip at understanding the underlying and interacting mechanisms to be ultimately able to customize nutrition to individual needs.

As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy. Coming from William C. Dement, one of the pioneers of contemporary sleep research, this statement depicts sleep as a neurobiological black box. One of the best ways to probe such black boxes is through exceptions, and olfaction stands out as such an exceptional sensory system during sleep. Specifically, whereas sensory stimuli presented during sleep typically wake, this is not the case with odors. In fact, odors may promote sleep. In turn, they remain processed by the sleeping brain, and provide a telling window onto sleeping brain capabilities. Here, we briefly review the foundations of sleep, and then extensively detail the literature on olfaction in sleep, concentrating on studies in humans. We speculate that the unique interplay of sleep and smell whereby odors are processed in sleep without causing wake reflects unique aspects of olfactory neurophysiology, particularly the direct projections from periphery to cortex without a thalamic relay. Finally, although the mechanisms allowing odor processing during sleep without arousal remain unclear, this phenomenon lends itself to using olfaction as a window onto sleep mentation. This approach has uncovered several aspects of learning and memory during sleep. We review these efforts, and conclude with detailing their potential application in the treatment of disease.

The trigeminal nerve is the fifth and thickest cranial nerve and not only it is responsible for facial sensation and motor functioning, but it is also responsible for chemosensory perception. On top of innervating the skin of the face, the trigeminal nerve also innervates the mucosa of the nose and mouth. Here, chemosensory perception starts with the activation of different receptors, the most important and best known ones being the transient receptor potential (TRPtransient receptor potential (TRP)) channels which give rise to sensations such as burning, warmth, coolness, coldness, and pain. From the mucosa, the trigeminal chemosensory information is conveyed through the trigeminal ganglion to the thalamic nuclei in the brain stem; from here fibers project to both, the somatosensory cortex and chemosensory areas of the brain.Most odors stimulate the trigeminal system, in addition to the olfactory system, especially in higher concentrations. However, overlaps between both sensory systems are not limited to the stimulus level, as they interact with each other on peripheral (mucosa) and central (brain) levels. As a consequence, subjects with a lacking olfactory system show lower trigeminal sensitivity and subjects with a lack of trigeminal sensitivity show lower olfactory activations.Different techniques are available to assess the state and the functionality of the trigeminal system. Such techniques include behavioral assessment by testing participants lacking a sense of smell – in order to exclude olfactory interference – as well as administrating different types of stimuli (pure odorants, pure trigeminal, or a mix of both). More objective measures include electrophysiological methods that evaluate the peripheral and central activations via the negative mucosal potentials (NMPs) and the trigeminal event-related potentials (ERPevent-related potential (ERP)s), respectively, as well as functional magnetic resonance imaging, and to a lesser extent, positron emission tomography (PETpositron emission tomography (PET)).

In everyday life, odorous sensations are a multisensory experience. In other words, odors are perceived before, during, or after inputs of other sensory systems like the visual, gustatory, auditory and tactile system. Thus, multisensory processing of olfactory cues should be assumed as a realistic stimulation for the perception of odors.Odors are perceived through two main pathways: orthonasal and retronasal routes and odors are processed in a different manner depending on the pathway. Therefore, before reviewing effects of other sensory cues on olfactory perception, both orthonasal and retronasal olfactory systems are discussed at psychophysical, cortical electrophysiological and neuroanatomical levels.This chapter introduces cross-modal correspondence between olfactory and other sensory cues; it also features the effects of other sensory inputs, such as visual, gustatory, auditory, trigeminal and tactile cues, on olfactory perception, with a focus on key modulators in cross-modal integration.Overall, most of the cross-modal integration between olfactory and other sensory cues appears to occur at a central nervous level. Many studies have emphasized the role of congruency between bimodal cues in cross-modal integration. The modulatory effect of congruency was found to be influenced by many factors such as odor delivery route (orthonasal and retronasal pathways), selective attention, experience (associative learning), cultural background, type of given task (analytical versus synthetic) and characteristics of a given stimulus.

The analysis of volatile organic compounds (VOCvolatile organic compound (VOC)s) is now accessible to almost any laboratory using gas chromatography coupled to mass spectrometry (GCgas chromatography (GC)-MS). With mass spectrum libraries now being well populated with thousands of molecules, structure elucidation is no longer a hurdle in most cases. Two-dimensional GC-MS and high-resolution MS systems facilitate the interpretation and accuracy of VOCs analysis (Chap. 17). Sample preparation techniques have also significantly improved. VOCs extraction can be performed using polymer absorbents, but the drawback is that the equilibrium of VOCs between the matrix and the polymer may reflect an analytical profile that does not correspond to reality. This chapter focuses on the common VOCs profiles in body odors, human urine odors and fecal odors. Analytical strategies are discussed. These VOCs are classified by chemical functionalities and their importance to the smell is discussed in detail.

Human axilla odors are only formed once skin secretions come into contact with the skin microflora. Axilla odors are thus a product of an intricate interplay between skin bacteria and axillary gland secretions. The bacterial populations in the axilla are dominated by Staphylococci and Corynebacteria. The magnitude of odor formation is associated with the population density of Corynebacteria on the skin of human panelists.In recent years, amino-acid conjugates were identified as the key secreted odorant precursors: Different odorant acids are secreted as glutamine conjugates, whereas sulfur volatiles arise from the bacterial degradation of conjugates related to glutathione. Specific enzymes were identified in Corynebacteria cleaving these amino-acid conjugates and thus releasing the odors.Based on this molecular understanding, questions on the evolutionary significance of these odors could be asked. The pattern of secreted odor precursors appears to be stable within an individual and it is genetically determined as was shown in a twin study. Based on behavioral studies, an association between axilla odors and the human leukocyte antigen (HLAhumanleukocyte antigen (HLA)) genotype had been proposed, but the chemical nature of potential HLA-associated body odors remained enigmatic. A family study on siblings with identical HLA-genes could not identify a link between genetically inherited patterns of glutamine conjugates and HLA-types.Axilla odors are largely absent in a significant fraction of the human population in the Far East. This has been associated with a single nucleotide polymorphism (SNPsingle nucleotide polymorphism (SNP)) in the ABCC11 gene. Indeed, human subjects lacking a functional ABCC11 allele are not able to secrete the amino-acid conjugates of the key odorants, which confirm the relevance of these biochemical mechanisms of odor formation identified in the last decade.

Humans produce numerous volatile compounds from different areas of the body, either as a direct result of metabolic processes or indirectly via metabolism of resident microflora. Body odors vary between individuals, partly due to genetic differences, but odors of the same individual also vary across time due to environmental influences. We discuss how at least part of the genetic influence appears to be related to certain personality characteristics and to sexual orientation. We then review the current state of the art in terms of intraindividual variation, including effects of intrinsic factors, such as hormonal influences on body odor and environmental factors, namely effects of diet and certain diseases. Some of these changes can be perceived by other individuals and might therefore provide social cues of current motivational, nutritional, and health status. Finally, we discuss how specific odor profiles associated with certain infectious diseases and metabolic disorders can be used as a cheap and efficient medical screening tool.

Human chemosensory signals are able to transmit a wide range of social information to conspecifics. Resulting from the interaction of several genetic and physiological processes (e. g., metabolic, immune, nervous), each individual produces a unique odor signature. The central processing of such chemosignals by conspecifics modifies physiological, behavioral, and psychological responses. To illuminate the importance of this mode of communication, we describe how humans produce, decode, and respond to warning chemosignals. Behavioral evidence highlighting the cognitive and emotional consequences of body odor communication will be discussed. Special attention will be devoted to the current understanding of human body odor neural processing. After an overview on the topic, we discuss the role that social chemosignals may have in our everyday life in health and disease.

Social communication refers to a basic human need, and findings accumulate that show humans communicate numerous kinds of social information via chemosignals. Briefly, it will be introduced which chemicals are conveyed through body fluids and which sensory systems are considered to process social chemosignals. Then, it will be shown that pheromones in humans have not yet been discovered. Studies on putative pheromones in humans often are performed disregarding the biological underpinnings of chemical communication and seem randomly to investigate volatile substances without any theoretical background. However, evidence will be provided that human chemosensory communication has been well demonstrated, using natural body fluids (e. g., sweat) as the source of chemosignals. Humans can decode information about the immunogenetic profile and the level of sexual hormones from volatiles released from the sweat of other individuals. These chemical signals are considered to affect mate choice. However, the signal extraction also depends on the sexual orientation of the perceiver. Furthermore, the recognition of kin and mother-infant communication comprise the release and decoding of chemosignals. Both phenomena are important prerequisites for the formation of social bonding and harm protection. Finally, the communication of stress and anxiety in humans will be presented as an example of a chemical transmission of emotional states. At the end of the chapter it will be questioned whether chemosensory communication is a skill, protective for certain mental disorders.

Talking about food is essential in our life. We love certain products, others are disgusting. While eating and drinking, we might express spontaneously our perceptions that foods have triggered. The range of reactions include nonverbal behavior, changing our facial expressions and bodily movements, verbal statements of liking and disliking including emotional and evaluative judgements, as well as analytical and neutral or objective descriptions. Our evaluation starts off with the perception of visual stimuli and volatile compounds eliciting an olfactory impression to the perception of various sensory modalities during breakdown of the food including taste, retronasal aroma and texture, as well as trigeminal impressions. As human beings, we use our senses to judge the quality of food. However, it is not always straightforward to verbalize what is perceived for all sensory impressions. Olfactory impressions are known to be difficult to describe. This chapter elaborates on language for odor descriptions from a language perspective with focus on the German and English or translated vocabularies. Culture and language are closely connected and shape the way we talk about olfactory impressions. Insights are given into vocabularies of people who are trained in describing food products and in everyday language, principally, what we experience in daily life when we are confronted with sensory stimuli.

The scent creation process consists in creating an original and attractive combination of fragrance ingredients. As the great perfumer Jean Carles said in 1961 perfumery is an art, not a science. Perfume creation indeed is far from easy and results from an extensive work of olfactory training and memorizing. Moreover, various parameters now have to be taken into account to develop a new fragrance. Technical aspects, such as performance, stability, as well as regulation and toxicology induce new issues that perfumers have to consider during the creation process. Perfume creationperfumecreation is thus at the crossroads of creativity and technology, art and science.

Immersive environments provide a computer-generated virtual reality for their users. They are applied in various fields such as engineering, marketing and sales, education and training, therapy or entertainment. Besides the dominant visual aspects or acoustic perception, olfactory perception can be one of the addressed senses in such a multimodal experience. The purpose is to immerse the user in a virtual scene in order to support decision making and design processes as well as learning. While odor can fulfill several functions in human–computer interaction there is currently no big market for computer-controlled scenting devices. Such devices should provide at least a subset of the functions of scent synthesis, dispensing, diffusion/ventilation, neutralization and exhaustion. Immersive environments in addition have to provide an interactive realtime experience and need to be controlled in synchronization with the other experiences and the scene context. This requires the integration of the olfactory simulation with the scene graph. Simple event-driven control models can be used as well as more complex fluid dynamics models to achieve a credible experience. Repeated attempts in previous decades to introduce scenting devices into mass markets for entertainment such as cinema and games were not successful. A more likely development path is the development in the aroma application industries, for example wearable devices for dispensing and dosing scent and aromas.

Marketers are increasingly using scent for differentiating, enhancing, and promoting products, and services. The spreading commercial use of scent, however, stands in contrast to a limited and fragmented body of knowledge on how people as consumers perceive and respond to olfactory stimulation. To facilitate a better understanding of opportunities and limitations to the commercial use of scent, this chapter reviews the state of research in the psychology, consumer behavior, and marketing literature. Extant studies examine scent as a primary product attribute, a secondary product attribute, an agent for promotional efforts, and as an ambient cue. Organized in six major sections, the chapter starts with a discussion of effective characteristics and the human processing of scent. A comprehensive review of consumer responses to scent follows. Section 56.4 adopts a multimodal perspective to illustrate how scent interacts with other sensory modalities to influence consumers as multisensory beings. Section 56.5 highlights individual and situational factors that can enhance or mute olfactory effects. The chapter concludes with a discussion of ethical aspects and outlines avenues for future research that may prove beneficial to both researchers and practitioners.

From the five senses (according to Aristotle), the sense that first comes to mind when thinking about space is the visual sense. Indeed, much of spatial experience is derived from vision. In this article, it is postulated that an equal consideration of all senses however can lead to a refined architectural designarchitectural design method and designed space.In particular, spiritual spaces offer often an experience beyond the visual. The space reception is thus multisensorymultisensoryfive senses; influenced by such factors as incense, darkness, coldness, and awe. All those stimuli constitute an intense, dense architectural atmosphere. If such an overlay of senses is possible, is it also possible to void a space of its stimuli? A study at the University of Applied Sciences in Augsburg came to the conclusion that a neutral space is impossible to design. Senses are essential to the human being and as soon as a space is emptied of this quality, its abstraction is perceived as nonhuman (mad-house) and thus as a negative space. Thus, the creation a positively perceived space was aimed for: one in which a majority of users feel welcomed at and comfortable in. This architectural answer can be utilized for test laboratories to avoid the potential negative perception by the sixth sense: that of anxiety when entering a testing environment.

Microdosing systems based on micropumps, which are applied nearby the nose, will enable the change of scent impressions of human nose at every breath several times a minute. Due to the small dosing volume the scent impression can be detected only once, and no other person in the room can smell the scent. With that, for the first time scent scenarios become possible, analogous to picture scenarios (movies) and sound scenarios (music). Such vision of scent scenarios can be combined with audio and video for applications in the movie, games, and music industry. The technology could also enable new applications for other branches like training of tasters (wine, food) or training tools for sense of smell for kids or adults.To realize this vision, both small and cost-efficient micropumps as well as a tight reservoir technology with small dead volume to provide scent molecules to be dosed are required. This chapter is discussing the dosing chain of scent from the reservoir to the nose, the dynamics of single-breath scent dosing as well as the state of the art of microdosing systems and micropumps.