Detection odor threshold, definition

ODOR. An important property of many substances, manifested by a physiological sensation caused by contact of their molecules with the olfactory nervous system. Odor and flavor are closely related, and both are profoundly affected by submicrogram amounts of volatile compounds. Attempts to correlate odor with chemical structure have produced no definitive results, Objective measurement techniques involving chromatography are under development. Even potent odors must be present in a concentration of 1,7 x I07 molecules/cc to be detected. It has been authentically stated that the nose is 100 times as sensitive in detection of threshold odor values as the best analytical apparatus. 

The sensory evaluation differentiates between the stimulation threshold (a just detectable level where a perceptible but not yet definable deviation of the sample from the standard is observed) and the recognition threshold, a level where the odor is identifiable or creates odor problems (a no longer tolerable quality deterioration caused by a definite off odor and/or taste). The difference between a perceptible and identifiable level is usually only one to two steps of a geometric dilution series. Therefore, only undifferentiated odor and taste thresholds are given in Table 13-6, because of the very different sensitivities of individual testers. The perceptible (stimulation) levels of a less sensitive tester can overlap with the identifiable (recognition) level of another more sensitive tester. 

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... 

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