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 threshold of a chemical compound is determined in part by its shape, polarity, partial charges, and molecular mass. The olfactory mechanisms responsible for a compound's different detection threshold is not well understood. As such, odor thresholds cannot be accurately predicted. Rather, they must be measured through extensive tests using human subjects in laboratory settings.

Optical isomers can have different detection thresholds because 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.

For raw water treatment and waste water management, the term commonly used is Threshold Odor Number (TON). For instance, the water to be supplied for domestic use in Illinois is 3 TON.[1]

Values
  • The threshold value is the concentration an aroma or taste can be detected (air, water and fat).
  • The recognition threshold or arousal threshold of olfactory neurons is the concentration at which you can identify an odor (air, water and fat).
  • The odour activity value 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 concentration 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.[2]

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)[3]
  • p-vinylguaiacol (OTV = 10 ppb)[4]

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 pH of the food. Some aroma compounds are affected by the pH: weak organic acids are protonated at low pH making them less soluble and hence more volatile.
  • Number and functionality of odorant receptors in the observer's nose.

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.

See also

References
  1. Lin, S (1977). "Tastes and Odors in Water Supplies - A Review" (PDF). Department of Registration and Education. 127: 1.
  2. L.J. van Gemert (2003) Flavour thresholds
  3. Sabine, Widder; Symrise GmbH & Co. KG. "8-tetradecenal as fragrance and flavoring substance". Google Patents. Retrieved 20 July 2017.
  4. H.H. Baek, K.R. Cadwallader (1999) Contribution of Free and Glycosidically Bound Volatile Compounds to the Aroma of Muscadine Grape Juice Journal of Food Science 64 (3), 441–444 doi:10.1111/j.1365-2621.1999.tb15059.x
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