FLAVOURINGS: ANATOMICAL-PHYSIOLOGICAL BASIS (I)
ORGANOLEPTICS PROPERTIES OF THE FOOD
- The acceptability of a food depends on the organoleptic properties and sensory.
- The organoleptic answer is due to the combination of sensations perceived.
- FLAVOUR = TASTE + SMELL
- ASPECT = TEXTURE + COLOUR
TASTE, SMELL AND FLAVOUR
- Exists confusion between “taste” and “flavour”.
- The differents “tastes” are limited and defined, the combinations of the “taste” are almost infinite.
- The selection of food and the perception pleasant or unpleasant depends of factors as age, the previous experiences, or, prenatal or congenital circumstances.
- The animals evolve in their preferences by the experience and learning, among these the aroma of the maternal diet.
- The responsible compounds of the aroma and of the flavour are components that are in less concentration, but has a fundamental effect on quality and acceptability of the food.
THE SELECTION OF THE FOOD
The wild animals:
Search the food through a chemicosensory mechanism that detects the nutritional value of the disposal sources.
The chemosensory system (located in the oronasal cavity) detects the dietetic nutrients and favours or difficults their posterior consume.
The domestic animals:
Little or no capability of election of food.
The peripheric sensors detect the cephalic phase of consume of food.
Direct impact and immediate (short term) in the beginning of the ingestion and size of it.
Consequence in their production and corporal development.
THE SENSORIAL PERCEPTION: THE TASTE
- The taste sensation is considered a multidimensional phenomenon, of 5 primary sensations, which correspond to a compound:
- Another phenomenons in the perception, that complete and modify:
THE SENSORIAL PERCEPTION: THE SMELL
- The olfactory sensations depend on the primary sensations.
- The combination of olfactory sensations characterize the aroma.
- Typical attributes of odor:
- Floral (jasmine)
- Spicy (gingerol, pepper)
- Fruity (ethyl acetate)
- Resinous (resin smoke)
- Fetid (rotten egg)
- Burned or smoke (tar)
- Musky (muscone)
- Camphorated, rancid (isovaleric and butyric acid)
- Throbbing, acre (formic and acetic acid)
- The majority of natural aroma are complex, integrated by different elemental odors:
- Almond flavor (camphorated, floral, mentholated)
- Lemon (camphorated, floral, mentholated, spicy)
- Garlic (ethereal, spicy, fetid)
- Rancid (ethereal, mentholated, spicy)
THE SENSORIAL PERCEPTION: THE SPICY EFFECT
- The spicy sensations, not are tastes nor odors, depends on the sensorial organ that acts.
- It is related to the capability of volatilization.
- It has clearly effects on the ingestion.
- It has a tactile component of irritation that is detected in the lip mucosa and rhino pharynx.
- The spicy sensation is produced by 2 types of substances:
- Thyocianates: very light and volatile molecules.
- Alkylamides: complex and heavy molecules.
THE SENSE OF TASTE
- The information of the taste is collected in the tongue, in their specialized nervous receptors: grouped in taste buds. Parts:
- Apical part: microvilli in contact with the saliva, responsible for receiving of the molecules.
- Basal part: efferent taste nervous fibers.
- Every taste bud correspond to one of the primary stimulous of the taste.
- A substance with flavor makes losses in the negative potential depolarizing the cell.
MECHANISMS OF RECEPTOR ACTIVATION
TYPES OF MECANISM
- Ionotropic receptors.
- G protein-coupled receptor.
- Acid and salty flavours.
- Triggering stimuli are Na+ and H+ ions, existing a specific receptor for each.
- Induced by the entry of ions in the receptor cell.
- Opens calcium channels resulting in the liberation of neurotransmitters.
- If it is specific for a determinated receptor is interpreted in the brain as a flavor.
- Salty in the case of Na+.
- Acid in the case of H+.
G PROTEIN-COUPLED RECEPTOR
- Bitter, sweet and umami flavours.
- The “flavour’s molecule” actives an external receptors of membrane that specifically recognize.
- G protein-coupled receptor, that by way of cAMP (cyclic adenosine monophosphate) opens calcium channels and liberates neurotransmitters.
- Gustative stimulation causes the receptor cell is depolarized and issue an action potential, which will be transmitted to the next neuron, and thus follow the path of newly stimulated nerve.
TASTE NERVES I
- The innervation of the tongue with autonomic fibers, sensitive, sensory and motor is in charge of five cranial nerves:
* The lingual nerve is a branch of the mandibular nerve, at the same time branch of the trigeminal nerve, that provides sensory innervation to the tongue.
TASTE SENSITIVITY I
- The tongue is not uniformly sensitive along its surface.
TASTE SENSITIVITY II
- Several studies demonstrate that a taste bud from the “sweet” region also respond to other tastes but in a minor way.
- Also, there are taste buds in palate, pharynx and in the top of the esophagus.
- The presence of cornified zones in the tongue (as in cows and hens), affects negatively the number of taste buds resulting in a minor gustative capability.
TASTE SENSITIVITY III
THE OLFACTORY SENSE
- Because of the sophisticated olfactory sense, the living beings modify their behaviour and establish the taste for certain environments and foods.
- The olfactory nerve is exclusive of the vertebrate animals.
- The olfactory sense of all mammals retains certain similitude in the nasal cavity, as localization and association with upper respiratory tracts.
THE OLFACTORY SENSE II
The odors code is differentiated by multiple receptors.
Different odors are recognised by their combinations.
– The selection is not specific, it’s situated in a molecular level =.
– Exists agonism and antagonism between odors and receptors
An unique type of fragrant molecule can interact with many receptors, thus, global sensation
is the result of the action of various activated receptors.
ACTIVATION OF THE OLFACTORY RECEPTORS I
- Basic receptors to detect odors:
- Primary receptors of invertebrates
- The receptor is a neuron, sometimes modified.
- Secondary receptors
- Specialized epithelial cells that form synapse with neurons.
- Sense considered primitive, because olfactory cells are bipolar neurons, originally from central nervous system = “primary” receptors
- Primary receptors of invertebrates
ACTIVATION OS THE OLFACTORY RECEPTORS II
- The mucous extreme of the olfactory cells forms a bud called “olfactory vesicle”, where born a lot of cilia (olfactory hairs) that penetrate in the mucus that cover the intern surface of the nasal cavity.
- The olfactory receptors respond to volatile agents in thousandths of a second.
ACTIVATION OF THE OLFACTORY RECEPTORS III
- Characteristics of odorant molecules:
- Volatiles (high steam pressure) to arrive to the olfactory mucosa.
- Lower polarity.
- Dipole moment.
- Certain surface activity.
- Partially soluble in water to penetrate in the aqueous mucosa of olfactory membrane and in the fats to penetrate in the lipid layer of the nervous cell membrane.
- Molecular weight lower to 400 daltons.
ACTIVATION OF THE 0LFACTORY RECEPTORS IV
- Olfactory receptors are adapted, approximately in a 50%, after the first second of stimulation.
- Fundamental characteristic:
- Quantity of stimulant agent needed in the air to trigger an objective sensation.
- The smell is more occupied in determine the presence or the absence of a certain odor than establish their intensity.
IDENTIFICATION AND DISCRIMINATION OF ODORS I
- The odorants:
- little organic molecules
- lower of 400 Da
- can vary in the number of parameters
- (size, form, number of groups, charge)
- Detected and discriminated by olfactory system.
- Receptor proteins have different molecular shapes with the capability of permit the attachment with a determined odorant molecule.
IDENTIFICATION AND DISCRIMINATION OF ODORS II
- A certain olfactory receptor has a range of acceptation of different odorant molecules.
- Sometimes, they act as inhibitors, due to certain structural similarities that compete between them for the union to a determined receptor.
- The complexity of the olfactory system: from chemical structure of odorant molecules decodified the information of the environment for recode later in the brain cortex. The result of this reconstruction is the olfactive sensation.
IDENTIFICATION AND DISCRIMINATION OF ODORS III
- The olfactory software
- Use a wide net of neurons to distinguish parts from the brain (mainly bulb and brain cortex).
- Use odor patterns stored in the memory.
- It is an emergent system, firstly simple but growing in complexity in function of needs.
- Richard Axel and Linda Buck (Columbia University) cloned and characterized 18 different members of a gene family that codify proteins, which act as olfactory receptors in the chromosome 1. In 2004, they received the Nobel Prize in Medicine and Physiology by this work.
IDENTIFICATION AND DISCRIMINATION OF ODORS IV
- The olfactory receptors act as letters of an alphabet with 347 letters.
- The codification of odors in a molecular level acts as a combinatory lock.
- The number of possible combinations, selected in groups is astronomical
- An odorant molecule can be recognised by various receptors.
- An olfactory receptor can recognise various odorant molecules.
IDENTIFICATION AND DISCRIMINATION OF ODORS V
– Slight changes in the chemical structure, active different types of receptors, in consequence, the smell of a molecule varies considerably.
– Some molecules show different odors in function of the concentration.
– Mix of two odorants, activate new neurons of brain cortex, that they were not activated by their individual compounds.
– An unique odorant compound is specifically recognised by multiple olfactory receptors that work jointly
THE THEORIES OF THE ODOR
– The form theory (Moncrieff, 1949): the molecules linked to receptors act in a key-lock system.
– “Molecular basis of odor” (Jhon E. Amoore, 1969): stereochemical theory indicated that molecular structure was related with the olfactory character.
– Weak form theory: the olfactory receptors only recognise the form of determined molecular parts.
– Vibrational theory (Luca Turín, 1996): the olfactory receptors act as tiny inelastic spectroscopes with tunnel effect placed in the olfactory ephitelium. He argued that activation of G protein permits the transduction of the electric impulse that will arrive to the olfactory bulb through neurons and the Zn2+ acts a chemical reaction cofactor. The linking between the odorant molecule and the receptor depends on the odorant molecule form.
– The new stereochemical theory (combinatory lock model) can be the rightest.
COMBINATION LOCK MODEL
- The odorant molecule binds to a protein by electrostatic attraction (Van der Waals forces).
- Probably is involved a metallic cation (Zn 2+) linked to a protein (metalloprotein).
- The odorant interacts with the protein causing a conformational change that produces the liberation of G protein.
- Certain molecules act as inhibitors, blocking the active centers of the olfactory receptors.
- Each olfactory glomerule recollect the information of a range of odorants that share similar molecular characteristics.
- The glomerules with similar molecular range are placed close, forming clusters.
THE TRANSMISSION OF THE STIMULUS I
- Protection law: all conscious and unconscious sensation has to be transmitted or projected to the brain to give an answer after interpretation.
- Transduction: process to transform a stimulus of potential membrane, that can be transmitted.
- The olfactory receptors, as primary receptors, are simple, because receptor potential and generator potential are the same, there’s no intervention of neurotransmitters nor synapse, before generate the action potential.
THE TRANSMISSION OF THE STIMULUS II
– Olfactory cortex neurons have reciprocal connections with other regions in the olfactory cortex (intrinsic connections) including direct connections with the orbitofrontal cortex, hypothalamus, amygdala, hippocampus and through the dorsomedial nucleous of the thalamus.
– The axons that born in the receptor cells are directly projected to neurons in the olfactory bulb that at the same time send projections to piriform cortex in temporal lobe and other structures of anterior encephalus.
THE TRANSMISSION OF THE STIMULUS III
– Other olfactory connections, are established with hypothalamus and with nervous nucleuses situated in front and above of it, related with primitive responses against odorant stimulus as salivation or lick lips, when is perceived nice odors related to food or the reproductive activity as secretion of gonad-stimulating hormones in males when detects the characteristic odor of the female in zeal.
THE TRANSMISSION OF THE STIMULUS IV
- The olfactory system is unique in the sensory systems, because don’t need a thalamic relief from primary receptors in their way to neocortical region (six layers) that processes the sensory information.
- The additional processing, produced in these different regions, identify the odorant and starts motor, emotional and visceral reactions appropriate for the olfactory stimulus.
THE TRANSMISSION OF THE STIMULUS V
NEURON OLFACTORY CONNECTIONS I
- Direct connection from olfactory bulb with the limbic system (sensations, emotions and memories) and the hypofisis.
- By the hypothalamic axis, is connected with the peripheral nervous system (mainly parasympathic system) that regulate secretory and motor functions from the digestive system.
- Olfactory sensations originate conscious and unconscious reactions.
NEURON OLFACTORY CONNECTIONS II
- The limbic system is a set of neuronal structures, phylogenetically, has a close relationship with the olfactory path, achieving in the mammals the range of major signification in the accomplishment of two great vital functions: self-preservation and the preservation of the specie.
The frontal lobe (the neocortical region more important in the limbic system), is the unique region that has direct connection with hypothalamus
NEURON OLFACTORY CONNECTIONS III
- The hypothalamus is involved in:
- Ingestion of food and water.
- Corporal metabolic activity.
- Growth regulation.
- Stress response.
- Hydrolytic balance regulation.
- Control of the corporal temperature.
- Sexual activity.
- Birth mechanism.
- Secretion and excretion of milk in lactating female.
- Participates in the mechanisms that interacts in multiple behavioural actions.
NEURON OLFACTORY CONNECTIONS IV
- The hypothalamus, to accomplish their functions, establish a close neuroendocrine relationship with different neuronal and glandular structures.
- These connections demonstrate that certain high intensity sweeteners (not carbohydrates) could be involved in the start of a appetite generator response in piglets, improving the ingestion through post-ingestive events.
EVOLUTION OF THE SMELL IN ANIMALS I
- The species evolution is linked to the evolution of olfactory structures.
- Among the visual sense and olfactory sense exists an inverse relationship.
- When more closer is head to the soil more important is the olfactory behaviour.
EVOLUTION OF THE SMELL IN ANIMALS II
- Judgement of the delicacy, sensibility and development of the olfactory development:
- By the size of the olfactory bulbs.
- By complexity of olfactory surfaces.
- By animal habits.
EVOLUTION OF THE SMELL IN ANIMALS III
- Olfactory superiority:
MAMMALS > BIRDS > HUMANS
- The hens has an important number of olfactory receptors in their DNA.
Birds retain their olfactory possibilities, although their different species have developed capabilities according to needs
EVOLUTION OD THE SMELL IN ANIMALS IV
- Aromas in animals have practice finalities, in humans, also, ludic.
- Olfactory capability measurement = olfactory bulb morphometry.
EVOLUTION OF THE SMELL IN ANIMALS V
- The dinosaurs used the smell to discover dangerous predators and locate tasty food.
- Millions of years ago, winged creatures, had best olfactive sense.
- The olfactive sense, in fact, improved during the transition dinosaur-birds, like vision or equilibrium, the ancestor of the birds (95 million years), developed best olfactory capabilities.
- Great advantages in modern birds to orient in the flight, seek food, companions and habitats as the combination of:
Olfactory sense more acute + good vision + coordination
- First mammals developed more big brains as a response to their strong olfactory sense and other vital senses.