Odor panel

Odor evaluation, in perfumes, 18 379 Odor impacts, air pollution dispersion modeling for, 26 725 Odorous compounds controlling, 10 75 in wastewater, 26 723t Odor panels, 26 724 Odor pollution, 26 669 Odor removal, adsorbents for, 1 611 Odors... 

The TOC may be defined as the absolute perception threshold (at which the odor is barely identifiable, but too faint) while the recognition threshold (100%) means the threshold concentration of the odorant whose odor may be defined (or accepted) by 100% odor panel as being representative odor of the substance being studied. By contrast, when 50% odor panel define the odor that is representative of the substance, then the above term becomes 50% recognition threshold . 

Sensory evaluation is a specialized discipline, using trained panels to measure and analyse the characteristics of food lipids evoked by the senses of taste, smell, sight and mouth feel. Sensory analyses are those most closely associated with the quality of food lipids, but their usefiilness is limited because they are costly and require a well-trained taste and odor panel and the proper facilities. However, sensory analyses provide sometimes ausefiil approach to identifying flavor or odor defects in the processing of food lipids that caimot be detected by other more objective chemical or instrumental analyses. For example, certain flavor defects characterized as grassy or fishy in linolenate-containing oils such as soybean and low-erucic rapeseed (canola) oils (Chapter 1) occur at such low levels of oxidation that they can only be detected by sensory analyses. The old term flavor reversion for soybean oil is based on the characteristic of this oil undergoing flavor deterioration at unusually low levels of oxidation that cannot be measured by peroxide value determination. Oils derived from fish... 

The types of flavors imparted by lipid oxidation in foods are more difficult to assess because there is wide variation in the sensory impact of different volatile products, and in the vocabulary used by taste or odor panels to describe their effect on quality. The diversity of sensory vocabulary used by different investigators to describe the same flavor defect in an edible oil has led to controversy on the origin of different flavor defects in soybean and other vegetable and fish oils. 

The sensitivity of taste or odor panels can be measured by the ability of individuals to detect sensory characteristics. Threshold values are measures of the least concentrations of volatile compounds detected in a food matrix (oil or water) or minimum detectable level by at least 50% of the panelists. This definition is, however, now commonly used to refer to detection by 100% of the panelists. There is a considerable difference in the flavor significance of volatile decomposition products formed in oxidized or rancid lipids. Hydrocarbons have the highest threshold values ranging from 90 to 2150 ppm, and the least impact on flavor. Substituted furans with threshold values of 2-27 ppm, vinyl alcohols with threshold values of 0.5-0.3 ppm, and 1-alkenes... 

Some contaminants in a gas stream are neither chemical pollutants nor objectionable particulates. They are malodorous materials that are considered a nuisance if vented into the atmosphere. The maximum desired atmospheric level of a malodorous substance is defined as that concentration just below the threshold of detection by 50% of an odor panel. Table 5-7 gives this detection limit for many common malodorous substances [10]. Note that many substances can be sensed by the olfactory nerves at levels below one part per billion. For instance, hydrogen sulfide can be detected to one fifth of one ppb, while butyric acid (the principal odor from rancid butter) can be detected to one half of one ppb. 

Metal Pan Assemblies. These units consist of tiles and panels formed from perforated aluminum or steel with pads of fiber glass or mineral wool inserted into the pans to provide the sound absorption. They are used primarily for ceilings in a similar manner to acoustical tiles and panels. The pads are sometimes sealed in plastic film to prevent absorption of moisture, dirt, and odors. The perforated metal is relatively sound transparent and functions as the finished ceiling and the support for the sound-absorbing material. The perforated metal by itself has no acoustical value. 

Taste and Odor. The measurement of taste and odor is somewhat subjective and depends on the personal judgements of individuals. Panels of not less than five observers, and preferably more than ten, are used. The sample is diluted with odor-free water until a ratio at which the odor is just perceptible is determined this ratio is called the threshold odor number (TON). A similar method is used to detect a distinct taste in water (see Flavor characterization). ... 

The sensory technique used for assessing human perception of odors is called olfactometry. The basic technique is to present odorants at different concentrations to a panel of subjects and assess their response. The process favored by the U.S. National Academy of Sciences is dynamic olfactometry (16). This technique involves a sample dilution method in which a flow of clean, nonodorous air is mixed with the odorant under dynamic or constant... 

Individuals differ in their sensitivity to odor. Figure 14-7 shows a typical distribution of sensitivities to ethylsulfide vapor (17). There are currently no guidelines on inclusion or exclusion of individuals with abnormally high or low sensitivity. This variability of response complicates the data treatment procedure. In many instances, the goal is to determine some mean value for the threshold representative of the panel as a whole. The small size of panels (generally fewer than 10 people) and the distribution of individual sensitivities require sophisticated statistical procedures to find the threshold from the responses. 

Odor threshold The minimum concentration of an odorous gas which 50% of a panel of trained sniffers can detect. 

Another valuable tool in food package development is the taste/odor Profile Test (18). Developed by the Arthur D. Little Company, this method uses a small panel of four to eight people specially trained in the procedure. Their analysis develops a full descriptive terminology for the product in question and assigns a numerical rating to each component of the taste/odor complex. 

A laboratory where the measurement takes place must be free from odor and is typically air-conditioned with air filtration. The odor sample is placed in an olfactometer that basically is a device for dilution of the sample. Typically, the meter has two outlet ports diluted odorous air flows from one, and clean odor-free air flows from the other. In dynamic olfactometry, panel members assess the two ports of the olfactometer. The assessors indicate from which of the ports the diluted sample is flowing. The measurement starts with a dilution that is large enough to make the odor concentration beyond the panelists threshold. This concentration is normally increased by a factor of two in each successive presentation. Only when the correct port is chosen and the assessor is certain that the choice is correct and not just a guess, is the response considered a true value. 

Olfactometric measurement should be undertaken in a room or area which is kept free from odors. There should be an atmosphere of comfort and relaxation in the test chamber, which will encourage panel members to concentrate on the testing task and not to be distracted by external stimuli. The test should be carried out at room temperature and normal humidity. 

Odor measurements must be carried out with the help of a team leader, who instructs the panelists and operates the measuring equipment. Communication between the team leader and the panel has to be kept to an absolute minimum. Because of fatigue, the duration of a test series as well as the time of the whole session should be limited. Breaks of at least the same duration as the proceeding test period should be provided. 

By convention the individual odor threshold is that concentration which is just perceived by the subject in 50% of the cases in which it is presented to him. The group threshold is the concentration that is just perceived by 50% of the panel members. 

Olfactory sensitivity for one individual varies about factor three due to climatological, physiological, environmental reaons etc. The sensory sensitivity also varies from odorant to odorant. So it is difficult to select a panel with a sensitivity distribution similar to that of the population. The preferred method in the United Kingdom for screening panelists uses the actual odor to be tested as a key component. In France selection is carried out on the basis of the threshold for five standard odorants. In Germany a normal sense of smell is requested of persons between the age of 18 and 50 years, in the Netherlands no exact specifications are given. Anyway, an extreme clustering around the mean or towards the extremes has to be avoided. 

The extent to which a panel constitutes a representative sample of the population depends directly on the numbers of panel members. For practical reasons a compromise must be sought between costs and the representativeness of the result, and this depends on the question to be answered basic measurement e.g. emission standards or only comparative measurements, e.g. odor abatement efficiency. 

---