Odor - The Electronic Nose Artificial Olfaction Technology - page 88

Fig. 4.2 Chemical molecule
odorants lead to the
perception of odor
• Person can smell at a distance.
• Many animals have keener sense of olfaction than man.
• Likes and dislikes often depend on association of the scent with pleasant or
unpleasant experiences.
To smell something the chemical must first become aerosolized, it must be
volatile. It must then dissolve in the mucus before binding to the olfactory cilia.
The chemical binding causes the bipolar neurons to depolarize. There are many (at
least a thousand) different receptor proteins on the membranes of the olfactory
cilia. A receptor protein may respond to several different chemicals and each
chemical may bind to several different kinds of proteins. The average person can
detect about 4,000 different odors. The odor is the perception experienced when
one or more chemical substances in the air come in contact with the various human
sensory systems (odor is a human response) [ 6 ], see Fig. 4.2 . Some odors may be
composed of one key chemical compound (one odorant); however, most often,
odors are a complex mixture of various chemicals (many odorants) [ 6 ].
4.5 Odor Parameters
Odors can be quantified by five parameters that outline the human response. These
parameters include: odor thresholds, odor intensity, odor persistency, hedonic
tone, and odor characterization.
4.5.1 Odor Detection Threshold
It is the lowest odorant concentration necessary for detection by a certain percentage
of the population, normally 50 %. This concentration is defined as 1 odor unit.
Odor detection capability or threshold or concentration is a sensory property
refers to the minimum concentration that produces an olfactory response. With
odor intensity at or just above ''threshold'' odor become difficult to perceive.
An odor detection threshold relates to the minimum odorant concentration
required to perceive the existence of the stimulus, whereas an odor recognition
threshold relates to the minimum odorant concentration required to identify the