Threshold recognition

The specific compounds that are responsible for the "pea" flavor have not been identified. Bengtsson and Bosund (52) suggested that acetaldehyde, hexanal and ethanol were important, while Murray et al. (53) isolated three methoxypyrazines that have very low taste or recognition thresholds and might, therefore, be of major significance in pea flavor. 

The odor sensitivity of an experimental animal needs to be known to appreciate communication distances and performance, but it is not easily measured. The detection thresholdhzs to be distinguished from the recognition threshold. The former is the concentration at which an odor is noticed, and the latter -typically much higher - the concentration at which behavior tests in animals or verbal responses in humans show that the odor has been recognized as a specific signal, compound, or mixture. 

Humans are extremely sensitive to hydrogen sulfide, most likely as a danger signal. The recognition threshold lies at 0.00047 ppm (vol) (cited in Cain, 1978). Only 40 molecules of methyl mercaptan, distributed over several receptors, sufficed for detection (cited in Harborne, 1993). 

Industrial effluents contain sulfur compounds, with their burnt, pungent quality, and fishy or ruinous-smelling nitrogen compounds. Humans are veiy sensitive to these odors hydrogen sulfide has an extremely low recognition threshold of0.00047ppm (vol.) (Cain, 1978). 

Dicyclopentadiene has a camphorlike odor with a 100% recognition threshold of... 

Sensory Evaluation. Results on the sensory evaluation of the three encapsulated powders showed that all three powders developed oxidized flavor even at first sampling time (3 days). Since an expert trained panel was used, the recognition threshold of members for oxidized flavor was far below the expected value. In addition, since oven stored samples were evaluated against freezer stored samples in the pair comparison test, panelists could not characterize the degree of difference in oxidized flavor between various powders. It is therefore suggested that lower storage... 

The threshold values determined in different liquids (water, oil, orangejuice, beer, sugar solution etc.) or less frequently, in air. The majority of the threshold values given are detection rather than recognition thresholds, although in many cases the type of threshold determined is not indicated in the original paper. 

Detailed investigations of structure and taste require quantitative data on the sensory side. The taste recognition threshold value is especially well suited for this purpose as, according to BEIDLER (8), it is connected with the association constant of the stimulus-receptor-complex. 

A fundamental concern of psychophysicists working on olfaction has been the determination of the odor thresholds of a broad array of substances. A distinction must be made between the detection threshold, which is the lowest concentration at which significant detection takes place that some odorous material is present, and the recognition threshold, which is the lowest concentration at which an odorant can be recognized for what it is. 

An earlier off-odor problem that surfaced was the presence of 4-phenyl-cyclohexene in styrene-butadiene coated paper (Koszinowski et al. 1980). This compound was created by a Diels-Alder condensation reaction involving a molecule of styrene and butadiene and is differentiated by its odor from the isomeric 3 and 1-phenyl-cyclohex-ene compounds which cannot be formed by such a condensation reaction. The recognition threshold of this compound in the headspace over an aqueous solution lies around a concentration of 10 pg/kg (10 ppb). The typical odor of this compound at concentrations of 4-phenyl-cyclohexene in paper over 4 mg/kg (4 ppm) is easily identified. AGC determination in this concentration range is also possible without difficulty and its identification with MS using the relative molecular mass of 158 and one of the retro Diels-Alder decomposition product fragments at m/e = 104 (styrene) and mJe = 54 (butadiene) is definitely possible. 

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. 

Linssen, J., Janssens, A., Reitsma, H., Bredie, W., Roozen, J. 1993. Taste Recognition Threshold Concentrations of Styrene in Oil-In-Water Emulsions and Yogurts. J. Sci. Food Agric. 61 457-462. 

Structural analogy with alkaloid compounds. One of these compounds, named quinizolate (13), exhibits an intense bitter taste at an extraordinarily low detection threshold of0.00025 mmol/kg of water. This novel taste compound was found to have 2000- and 28-fold lower threshold concentrations than the standard bitter compounds caffeine and quinine hydrochloride, respectively, and, therefore, it is claimed to be one of the most intensely bitter compounds reported so far [46]. It is important to note that in sensory evaluation there is a difference between detection threshold and recognition threshold the first determines the concentration of a substance that makes one able to say this is not pure water the second means that the panelist is able to state this is bitter. Therefore these reported data on the taste of new compounds must to be taken carefully especially in comparison with others. 

Arbisi, R A., A. S. Levine, J. Nerenberg and J. Wolf (1996). Seasonal alteration in taste detection and recognition threshold in seasonal affective disorder the proximate source of carbohydrate craving. Psychiatry Res 59(3) 171-82. 

In addition to the six-carbon volatile compounds, l-penten-3-ol is also found in all freshwater fish. However, concentrations of l-penten-3-ol in fish remain below its recognition threshold (400 ppb 38), and therefore it is unlikely that this volatile contributes strongly to the characteristic aroma of freshly harvested fish. 

Recognition threshold values (the concentration at which a certain chemical is recognised) are usually measured in the same way as detection levels. Both use either the method of limits or the method of constant stimuli [3]. 

The detection threshold is the lowest stimulus intensity (odour concentration) that the subject can distinguish from an odour-free situation. The subject s response indicates whether the presence of an odour has been perceived or not. Correspondingly, the recognition threshold is the minimum concentration at which an odour can be identified. 

Tamura et al. (this volume) discuss the suitability of the detection threshold and the recognition threshold in determining the limited odor unit for characterizing citrus aroma quality. 

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