Odor detection threshold
Encyclopedia
The odor detection threshold is the lowest concentration of a certain odor
compound that is perceivable by the human sense of smell
. The thresholds of a chemical compound is determined in part by its shape
, polarity
, partial charge
s and molecular mass
. The olfactory mechanisms responsible for a compound's different detection threshold is not well understood, as such, these thresholds cannot yet be accurately predicted. Rather, they must be measured through extensive tests using human subjects in laboratory settings.
Optical isomers can have different detections thresholds since their conformations may cause them to be less perceivable for the human nose. It is only in recent years that such compounds were separated on gas chromatographs.
of a substance that can be detected by a human nose
. Some substances can be detected when their concentration is only few milligrams per 1000 tonnes, which is less than a drop
in an Olympic swimming pool. Odor threshold value can be expressed as a concentration in water or concentration in air.
Two major types of flavor thresholds can be distinguished: the absolute and the difference threshold. The odor detection threshold
and the odor recognition threshold are absolute thresholds; the first is the minimum concentration at which an odor can be detected without any requirements to identify or recognize the stimulus, while the second is the minimum concentration at which a stimulus can be identified or recognized.
The odor threshold value of an odorant is influenced by the medium.
Examples of substances with strong odors:
The concentration of an odor above a food is dependent on its solubility in that food and its vapor pressure
and concentration in that food.
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...
compound that is perceivable by the human sense of smell
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
. The thresholds of a chemical compound is determined in part by its shape
Molecular geometry
Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...
, polarity
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
, partial charge
Partial charge
A partial charge is a charge with an absolute value of less than one elementary charge unit .-Partial atomic charges:...
s and molecular mass
Molecular mass
The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...
. The olfactory mechanisms responsible for a compound's different detection threshold is not well understood, as such, these thresholds cannot yet be accurately predicted. Rather, they must be measured through extensive tests using human subjects in laboratory settings.
Optical isomers can have different detections thresholds since their conformations may cause them to be less perceivable for the human nose. It is only in recent years that such compounds were separated on gas chromatographs.
Values
- The threshold value is the concentration an aroma or taste can be detected (air, water and fat).
- The recognition threshold is the concentration at which you can identify an odor (air, water and fat).
- The odor unit is the concentration divided by the threshold.
- The flavor impact is the value the rate of change in perception with concentration.
- The flavor contribution of an aroma component in a mixture to the total profile can be calculated from the total odor units and the number contributed by that aroma chemical.
Odor detection value
Odor threshold value (OTV) (also aroma threshold value (ATV), Flavor threshold) is defined as the most minimal concentrationConcentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
of a substance that can be detected by a human nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
. Some substances can be detected when their concentration is only few milligrams per 1000 tonnes, which is less than a drop
Drop (unit)
The drop is a unit of measure of volume, the amount dispensed as one drop from a dropper. It is often used in giving quantities of liquid drugs to patients, and occasionally in cooking....
in an Olympic swimming pool. Odor threshold value can be expressed as a concentration in water or concentration in air.
Two major types of flavor thresholds can be distinguished: the absolute and the difference threshold. The odor detection threshold
Odor detection threshold
The odor detection threshold is the lowest concentration of a certain odor compound that is perceivable by the human sense of smell. The thresholds of a chemical compound is determined in part by its shape, polarity, partial charges and molecular mass...
and the odor recognition threshold are absolute thresholds; the first is the minimum concentration at which an odor can be detected without any requirements to identify or recognize the stimulus, while the second is the minimum concentration at which a stimulus can be identified or recognized.
The odor threshold value of an odorant is influenced by the medium.
Examples of substances with strong odors:
- (Z)-8-tetradecenal (OTV = 0.009 ppb in water)
- p-vinylguaiacol (OTV = 10 ppbPPBPPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...
)
Variables
Threshold in a food is dependent upon:- The threshold of the aroma in air.
- Concentration in the food
- Solubility in oil and water
- Partition coefficient between the air and the food
- The pHPHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the food, some aroma compounds are affected by the pH - weak organic acids are portionated at low pH making them less soluble and hence more volatile.
The concentration of an odor above a food is dependent on its solubility in that food and its vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
and concentration in that food.