Flavour

From Food to Perception

Elisabeth Guichard, Christian Salles, Martine Morzel, Anne-Marie Le Bon, Elisabeth Guichard, Christian Salles, Martine Morzel, Anne-Marie Le Bon

• Publisher: Wiley-Blackwell
• Year: 2016
• Print ISBN: 9781118929414
• eBook ISBN: 9781118929391
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

This book will cover all aspects of flavour perception, including aroma, taste and the role of the trigeminal nerve, from the general composition of food to the perception at the peri-receptor and central level. This book will answer to a growing need for multidisciplinary approaches to better understand the mechanisms involved in flavour perception.

The book presents the bases of anatomy of sensory perception. It will provide the requisite basic knowledge on the molecules responsible for flavour perception, on their release from the food matrix during the eating process in order to reach the chemosensory receptors, and on their retention and release from and transformation by bodily fluids of the oral and nasal cavities. It will also bring current knowledge on the multimodal interactions.

This book will also cover the recent evolution in flavour science: characterisation of molecules, interaction with food matrix and more recently, physic-chemical and physiological and events during oral processing increasingly considered.

Chapter 1
Olfactory system in mammals: structural and functional anatomy

Anne-Marie Le Bon, Frédérique Datiche, Jean Gascuel & Xavier Grosmaitre

Center for Taste and Feeding Behaviour, CNRS, INRA, University of Bourgogne Franche-Comté, Dijon, France

1.1 Introduction

The survival and reproductive success of living organisms, including human beings, depends on the detection of sensory stimuli. Living organisms do not eat or reproduce with whatever is available; instead, they show considerable selectivity by taking advantage of their chemical and physical senses. In this regard, the sense of smell and its capacity to detect myriad of odorant molecules is of critical importance for humans and most animal species. This sense significantly contributes to the identification of food and assessment of its palatability, as well as to the detection of chemical compounds carrying specific information concerning dangers, social interactions and reproductive behaviours. In mammals, these diverse roles are accomplished by a complex olfactory system. The primary tissue responsible for sensing volatile odorants is the olfactory epithelium (OE) which is localized in the nasal cavity. Sensory neurons residing in the OE convey olfactory information to the olfactory bulb (OB) which, in turn, transfers this information towards multiple higher cortical regions collectively referred to as the olfactory cortex. Other olfactory subsystems such as the vomeronasal organ coexist with the main OE in many species. These subsystems are separate entities that are dedicated to distinct functional roles.

The principal aim of this review is to gather the results of very recent as well as major studies on the processing of olfactory information by the olfactory system and to highlight its plasticity. We first describe the physiology of the main OE and the molecular mechanisms of odorant detection. We then show how endogenous and exogenous factors may induce different forms of plasticity of the OE. We also outline the main features of other olfactory subsystems. Next, we examine how the olfactory signal generated at the peripheral level is transformed at the first processing center in the brain, the OB. Finally, we provide an overview of the higher olfactory pathways involved in the processing of olfactory information and we consider the pathways that shape odour perception.

1.2 Organization and function of the peripheral olfactory system

1.2.1 Physiology of the peripheral olfactory system

Stimulation of the olfactory system begins when odorant molecules are detected by the olfactory neuroepithelium located in the upper part of the nasal cavity. The odorant molecules can reach the epithelium by two pathways: via the nose (orthonasal olfaction) and via the mouth (retronasal olfaction). Odorants perceived by the orthonasal pathway originate from the external world whereas odorants perceived retronasally emanate from food or drink (aroma compounds) (see Chapter 13 for more details on these pathways).

The nose and the nasal cavity are separated into two halves along the midline by a cartilaginous structure called the nasal septum. The lateral wall of each nasal cavity is typically shaped by three bony protuberances termed the inferior, middle and superior turbinates. Animals can have more turbinates, for example, the rat has four. The turbinates and the septum are covered with an epithelium. Depending on its location, this epithelium is either nonsensory (respiratory) or sensory (olfactory). The nonsensory respiratory portion of the nasal cavity warms, cleans and humidifies the inspired air.

There is widespread acknowledgement that the human OE is located in the superior region of the nasal cavity, predominantly on the dorsal side of the nasal vault, the septum, and the superior turbinate. However, recent studies have reported a more extending distribution of OE on the middle turbinate (Escada et al. 2009). Actually, the location of the OE is variable among people. Besides, its organization is thought to change over time: ageing induces conversion to or ingrowth of respiratory epithelium and loss of olfactory neurons (Nakashima et al. 1991). Environmental compounds or pathophysiological processes such as infection or inflammation can also modify the distribution of OE. The OE in the adult has therefore a non-contiguous and patchy distribution. Globally, the human olfactory region covers between 1 and 2 cm² in each cavity (Moran et al. 1982). This area is modest relative to those of other vertebrates such as rodents and dogs (Gross et al. 1982, Harkema 1991).

In the superior part of the nasal cavity, a horizontal bone, called the cribriform plate of the ethmoid, separates the OE from the brain. The cribriform plate is a highly perforated bone: the perforations provide access for the olfactory nerve bundles to the OB. This is the only site in the body where the central nervous system is in direct contact with the outer surface. The nerves serving the olfactory region are called the first cranial nerves or the olfactory nerves. They concentrate multiple axons of olfactory neurons located in the lamina propria. These axons convey the nerve impulse generated by the odorant detection into the OB.

1.2.2 Structure of the olfactory epithelium

The human OE has a structure similar to that of other vertebrates (Morrison and Costanzo 1992). It is a pseudo-stratified columnar epithelium that lies on a dense connective tissue, the lamina propria. Together, the OE and the lamina propria form the olfactory mucosa (OM). The human OE is about

in height and has a slight yellow-brownish colour. It is composed of several distinct cell types, notably olfactory sensory neurons (OSNs), sustentacular cells (a type of nonsensory supporting cells), microvillar cells, two types of stem cells (horizontal basal cell and globose basal cell) as well as Bowman's glands and duct cells (Figure 1.1B).

Figure 1.1 Schematic drawing of the rodent olfactory system (sagittal cross section through the nasal region of the head, lower jaw is not shown). Inset A shows the different cell layers observed in the olfactory bulb and the neuronal connections. Inset B represents the various cell types and structures located in the olfactory mucosa. Inset C schematizes the connectivity of glutamatergic neurons in the PCx (Source: Adapted from Ekberg and St John 2014, Haberly 2001). Abbreviations: AOB, accessory olfactory bulb; aPCx, anterior piriform cortex; DP, deep pyramidal cells; EPL, external plexiform layer; FB, feedback interneurons; FF, feed forward interneurons; G, glomeruli; GG, Grueneberg ganglion; GL, glomerular layer; Gr, granule cells; GrL, granular cell layer; IPL, internal plexiform layer; LOT, lateral olfactory tract; M, mitral cells; MCL, mitral cell layer; Mp, multipolar cells; OB, olfactory bulb; OE, olfactory epithelium; ONL, olfactory nerve layer; pgC, periglomerular cells; pPCx, posterior piriform cortex; OSN, olfactory sensory neuron; SL, semilunar cells; SO, septal organ; SP, superficial pyramidal cells; T, tufted cells. A colored version of this figure can be found in the online version of this chapter.

Vertebrate OSNs are slender and bipolar neurons spread in the epithelium with a density of 10⁶-10⁷ per cm². Their cell bodies are generally located within the lower two thirds of the neuroepithelium. At the ...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• List of Contributors
• Preface
• List of Abbreviations
• Chapter 1: Olfactory system in mammals: structural and functional anatomy
• Chapter 2: Odorant metabolizing enzymes in the peripheral olfactory process
• Chapter 3: The vertebrate gustatory system
• Chapter 4: Bioadhesion and oral fluids—perireceptor modulators of taste perception?
• Chapter 5: Basic physiology of the intranasal trigeminal system
• Chapter 6: Characterization of aroma compounds: structure, physico-chemical and sensory properties
• Chapter 7: Characterization of taste compounds: chemical structures and sensory properties
• Chapter 8: Sensory characterization of compounds with a trigeminal effect for taste modulation purposes
• Chapter 9: Interactions between aroma compounds and food matrix
• Chapter 10: Aroma release during in-mouth process
• Chapter 11: Release of tastants during in-mouth processing
• Chapter 12: Interactions between saliva and flavour compounds
• Chapter 13: Orthonasal and retronasal perception
• Chapter 14: Perception of mixtures of odorants and tastants: sensory and analytical points of view
• Chapter 15: Odour mixture coding from the neuronal point of view
• Chapter 16: Multisensory flavour perception
• Index
• Food Science and Technology Books
• End User License Agreement