Odour Detection Methods: Olfactometry and Chemical Sensors

Abstract

The complexity of the odours issue arises from the sensory nature of smell. From the evolutionary point of view olfaction is one of the oldest senses, allowing for seeking food, recognizing danger or communication: human olfaction is a protective sense as it allows the detection of potential illnesses or infections by taking into account the odour pleasantness/unpleasantness. Odours are mixtures of light and small molecules that, coming in contact with various human sensory systems, also at very low concentrations in the inhaled air, are able to stimulate an anatomical response: the experienced perception is the odour. Odour assessment is a key point in some industrial production processes (i.e., food, beverages, etc.) and it is acquiring steady importance in unusual technological fields (i.e., indoor air quality); this issue mainly concerns the environmental impact of various industrial activities (i.e., tanneries, refineries, slaughterhouses, distilleries, civil and industrial wastewater treatment plants, landfills and composting plants) as sources of olfactory nuisances, the top air pollution complaint. Although the human olfactory system is still regarded as the most important and effective “analytical instrument” for odour evaluation, the demand for more objective analytical methods, along with the discovery of materials with chemo-electronic properties, has boosted the development of sensor-based machine olfaction potentially imitating the biological system. This review examines the state of the art of both human and instrumental sensing currently used for the detection of odours. The olfactometric techniques employing a panel of trained experts are discussed and the strong and weak points of odour assessment through human detection are highlighted. The main features and the working principles of modern electronic noses (E-Noses) are then described, focusing on their better performances for environmental analysis. Odour emission monitoring carried out through both the techniques is finally reviewed in order to show the complementary responses of human and instrumental sensing.

Room Temperature Ionic Liquids As Useful Overlayers for Estimating Food Quality from Their Odor Analysis by Quartz Crystal Microbalance Measurements

“…[1][2][3] In particular, odor analysis can provide valuable information on food quality and safety, which is especially welcome when achieved by simple, rapid, on-line and real-time detection methods. Thus, volatile organic compounds (VOCs) involved in food metabolic pathways (carboxylic acids, alcohols, carbonyl compounds, lactones) or food ripening (terpenes, esters, ethers) contribute significantly to agreeable flavors.…”

Innovative educational course II: Modelling of odour dispersion from agricultural biogas plants

“…This method also takes into account the odour mixture as a whole, so it is not able to distinguish individual chemical compounds [15]. It was also found that odour assessment results can be affected by psychological aspects of panellists too, because in some cases the panellists tend to guess the correct result instead of impartial assessment [16].…”

“…This signal is conducted by nerve fibres to the olfactory centre in brain where it is evaluated. The evaluation is done in such a way that the received signal is compared to information stored in memory [15]. As a result, the human knows which odour he or she smells (or which of the known odours this sensed odour resembles the most) and whether this odour is pleasant or not.…”

Experimental Tests on the Influence of Waste Covering Layer on Odour Reduction

“…The second sample was taken after one hour. Samples were taken at a height of several centimetres from the waste or building debris surface with the vacuum chamber AC'SCENT and collected to Tedlar bags of 10 dm 3 capacity and analysed in a laboratory on the same day [19]. The analysis was performed by the method of forced selection.…”