Technique olfactometric

Each case may provide features which influence the olfactometric measurements, often demanding special sampling techniques and interpretations. In the following some of the problems and experiences will be pointed out by means of examples from sewage treatment and fish meal plants, showing the use of olfactometry for obtaining satisfactory odour reducing results. 

Obviously this procedure involves a lengthy and complex follow-up to the original analysis. Furthermore it is important to note that although the analytical results are objective measurements, the appraisal of their effectiveness in describing the emission, ultimately relies on subjective comparisons of odour sensation. This final observation could be interpreted as a weakness in the method in having to resort to subjective odour comparisons. An alternative viewpoint however is that the most effective information can be derived by utilising a combination of olfactometric and physico-chemical techniques. 

Within Severn Trent a modified version of this procedure is utilised for the analysis of malodorous emissions. The most significant difference in this approach compared to those already discussed is the use of high resolution gas chromatography in combination with olfactory detection. This method also combines physico-chemical and olfactometric or sensory techniques but in an alternative manner. Utilisation of gas chromatography combined with odour detection is not a new concept and has been employed fairly commonly for the analysis of food aromas, essential oils and other fragrances. The technique is equally applicable to environmental problems and is used frequently in this laboratory for the analysis of atmospheric emissions and taste and odours in water. Three important benefits accrue from this approach in the context of odour emission analysis. 

In all research work, the set-up of the experiments, the sampling technique and the analytical methods ask for careful consideration and much common sense. This holds especially for olfactometric measurements. 

Aroma compounds of fresh banana from different countries (Martinique, Canary Islands, and Cote d Ivoire) were examined using the same extraction technique. As expected, differences in aroma composition were detected in the fruits of different origins. Isoamyl alcohol, isoamyl acetate, butyl acetate, and elemicine were detected by olfactometric analyses as characteristics of banana odour [7]. 

Since all aroma molecules are more or less volatile, the technique that a priori is best suited to screen the odor active molecules from the rest of molecules is Gas Chromatography-Olfactometry (GC-O). This technique makes use of the human nose as detector for the compounds eluting out of the chromatographic column, typically a fused silica capillary column (Acree et al. 1984). There are several different approaches for GC-O differing in the way in which the olfactometric signals are... 

GC in combination with olfactometric techniques (GC-0) is a valuable method for the selection of aroma-active components from a complex mixture (7). Experiments based on human subjects sniffing GC effluents are described as GC-0. This technique helps to detect potent odorants, without knowing their chemical structures, which might be overlooked by the OAV concept (ratio of concentration to threshold) if the sensory aspect is not considered from the very beginning of the analysis. Experience shows that many key aroma compounds occur at very low concentrations their sensory relevance is due to low odor thresholds. Thus, the peak profile obtained by GC does not necessarily reflect the aroma profile of the food. 

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