Odor - The Electronic Nose Artificial Olfaction Technology - page 84

Chapter 4
Odor
4.1 Introduction
The human nose is a sense organ that senses odors. Experiencing smell sensation
consists of the initial impacting of vapors on the sensor part of the nose. The sense
of smell has long played a fundamental role in human development and biosocial
interactions. Consequently, the olfactory sense has become a key element in the
development of many commercial industries that manipulate the aroma properties
of their manufactured goods in order to improve product appeal, quality, and
consistency so that consumers quickly identify with individual brands having
unique scents.
A more flexible way of presenting the primary odors to clarify the idea of
complex odors is through the use of Henning's odor Prism [ 1 ] (Fig. 4.1 ). Six
primary odors are located at the corners of the prism. All other odors are mixtures
of the primary odors and located on the surfaces and edges of the prism. Thus,
odors consisting of two components would be represented on the edges of the
prism, three component mixtures occupy the triangular surfaces, and four-com-
ponent mixtures occupy the square surfaces.
Odor can be defined as the ''perception of smell'' or in scientific terms as ''a
sensation resulting from the reception of stimulus by the olfactory sensory sys-
tem''. Whether pleasant or unpleasant, odor is induced by inhaling air-borne
volatile organics or inorganic. The sources of smell are volatile compounds of low
molecular weight (molecular weight \300 ppm) that are actually recognized as
odor. The estimated total number of odor-producing materials is around several
hundred thousand kinds of low molecular weight volatile compounds.
Materials that humans can perceive as odor include many organic compounds,
such as the aromatic series (benzenes), as well as compounds containing oxygen
(alcohol, aldehyde, ketone, and fatty acid), sulfur, and nitrogen, among others.
Among inorganic substances, fluorine, chlorine, bromine, sulfur, hydrogen sulfide,
nitrogen dioxide, and ammonia, etc., all possess objectionable odors [ 2 ].