Odor recognition threshold

One method of controlling response perseveration and other anticipation factors is to use a forced choice response indication based on two or more response categories. In the measurement of odors the panelist has to report the temporal position of positive stimuli in a series of random blanks. If the concentration is below the threshold, the test subjects will guess. As the odorant concentration will increase, the relative cumulative frequency for identification of the correct sample will be greater. In order to determine the relative odor recognition a correction must be made. 

The OI, is the ratio of vapor pressure to 100% odor recognition threshold. Both the terms, that is, the vapor pressure and the odor recognition threshold, are expressed in ppm. Therefore, the OI becomes a dimensionless term. 

Example. The vapor pressure of a volatile liquid at ambient temperature is 38 torr. Its odor recognition threshold as determined by 100% panel of observers is 200 ppb. Determine the OI of this substance. 

In general, a psychophysical measurement is more expensive and more tedious to obtain than a physical measurement. Compare, for example, the time and expense required to measure quantitatively an odor recognition threshold for particular molecule vs... 

The human sensory apparatus varies in sensitivity from person to person. Therefore, in the selection of panelists for sensory evaluation purposes the first step is to establish the limits of their sensory capacities by determining their perception thresholds for basic tastes, flavor, and odor recognition. 

As odor recognition threshold varies from individual to individual, this table should be used only as a rough guide. 

Odor data for the various amyl alcohols is limited. The lowest perceptible limit for 1-pentanol and / fZ-amyl alcohol are 10 and 0.04 ppm, respectively (135). tert-Axa[. alcohol has a threshold value of 2.3 ppm (and a 100% recognition level of 0.23 ppm) 3-methyl-1-butanol has an odor threshold of 7.0 ppm. The odor of 1-pentanol has been described as sweet and pleasant whereas that of 3-methyl-2-butanol is sour (135). 

Colorless, very mobile liquid with a very strong, acetic acid-like odor. Experimentally determined detection and recognition odor threshold concentrations were <600 pg/m (<140 ppbv) and 1.5 mg/m (360 ppbv), respectively (Heilman and Small, 1974). 

Clear, colorless liquid with a rancid sweet odor similar to fusel oil. Experimentally determined detection and recognition odor threshold concentrations were 900 pg/m (300 ppbv) and 3.0 mg/m (1.0 ppmv), respectively (Heilman and Small, 1974). Odor threshold concentration in water is 500 ppb (Buttery et al, 1988). The least detectable odor threshold in concentration water at 60 °C was 0.2 mg/L (Alexander et al., 1982). Cometto-Muniz et al. (2000) reported nasal pungency threshold concentrations ranging from approximately 900 to 4,000 ppm. 

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