Sensory thresholds

NGF has effects on the physiological responses of mature neurons. NGF acts as a target-derived trophic factor for pain neurons, which innervate peripheral tissues such as the skin. Inflammation of these peripheral tissues leads to local elevation of NGF synthesis and abundance. Elevated concentartions of NGF are responsible for the enhanced sensitivity to pain that accompanies inflammation. This is due to the ability of NGF to lower the sensory threshold of the pain fibers, leading to hyperalgesia. Nocioceptive sensory neurons mediating pain sensation are entirely dependent upon NGF for their survival as these cells are selectively lost in animal in which either the NGF or TrkA genes have been knocked out. These animals are insensitive to pain and live only a few weeks. 

Ugarte, S. D., Homanics, G. E Firestone, L. L and Hammond, D. L. (2000) Sensory thresholds and the antinociceptive effects of GABA receptor agonists in mice lacking the P3 subunit of the GABAa receptor. Neuroscience 95,795-806. 

Reliable quantitative data are a prerequisite for evaluating the contribution of a single odorant to a positive aroma or off-flavor. They are needed to calculate odor activity values (OAV) that are defined as the ratio of the concentration to the sensory threshold of a given compound in a matrix (Rothe and Thomas, 1963 Acree et al., 1984). These values give guidance in the evaluation of the impact of an odorant to the overall aroma profile. 

Literature information about the sensory properties for nearly 450 Maillard reaction products has been compiled in a survey. It includes qualitative aroma and flavor descriptions as well as sensory threshold values in different media for the compounds, classified according to their chemical structure. 

Determination of the sensory threshold PBP sequenced X94987 (Krieger et al. 1996)... 

The amounts of thiols formed during alcoholic fermentation are strongly affected by the previous development of B. cinerea (Table 6.7). Since these compounds have extremely low sensory thresholds, and seem remarkably stable in wine, 3SH particularly plays a significant role in the fruity aroma of botrytized wines (Dubourdieu and Tominaga, 2009). 

Sensory thresholds (in beer) and odor descriptors. a 5-Hydroxymethyl-2-furfuraI. h 5-Ethoxymethyl 2-furfural c Minimum. d Maximum. e Mean value. 

The sensory properties of nearly 450 volatile Maillard reaction products and related compounds have been compiled (45). The review includes quantitative aroma and flavor descriptions, as veil as sensory threshold values for different media, classified according to chemical structure. 

It should be pointed out, that we were concerned with presence or absence of bitterness. Bitterness in terms of sensory threshold values or bitterness ratings was not assessed. 

Bitterness in terms of sensory threshold values or bitterness ratings was not assessed. 

Styrene monomer concentration in foods packaged in 31 different PS-containing food packages and contact materials averaged 224 mg/kg with two products having concentrations between 800 and 1500 mg/kg, well above the sensory threshold limits (Baner, 2000). Strict specifications for styrene monomers as well as for residual solvents, toluene, and odor and taint transfer for supplier materials should be set (Huber et al., 2002). 

Due to their extremely low sensory threshold levels, chloro- and bromoanisoles have been clearly identified for years as the cause of off-odors. The following case shows how new variations and combinations of unpredictable events can lead to a problem whose solution requires a great amount of work. 

From experience it has been established that the sensory threshold for coffee creamer and condensed milk products is on the order of 0.1 mg/kg (ppm) of styrene in the product. This observation is only partly supported by threshold values from the literature in Table 14-2 where values range from 0.2 ppm for 3 % yogurt, 1.2 ppm for 3.8 % fat milk and 2-5 ppm for condensed milk. This points out two problems with threshold concentration values caused by the way they are determined (e.g. experimental methods) and the definition of the threshold value being the value at which the substance is correctly identified by 50 % of the panelists (versus other possible ways of measur-ing/defining the taste threshold). 

Interpretation of result The calculated migration values here are realistic since results calculated using Eq. (14-4) cannot be larger than the mass balance result (Example 14-1). The calculated amount of styrene is still above the assumed sensory threshold limit of 0.1 mg/kg in the product for the worst case in step 4 but is equal to the estimation using the experimental diffusion coefficient in step 5. 

Miltz, J., Elisha, C Mannheim, C. 1980. Sensory threshold of styrene and monomer migration from polystyrene food packages. J. Food Processing and Preservation. 4 281-289. 

At low levels (5 mg/L), diacetyl is considered to add complexity to wine aroma since it can impart positive nutty or caramel characteristics, although at levels above 5 mg/L it can resuit in spoilage, creating an intense buttery or butterscotch flavour, and is perceived as a flaw. Microbial formation of diacetyl is a dynamic process and its concentration in wine depends on several factors bacterial strain, pH, wine contact with lees, SO2 content (Martineau and Henick-Kling 1995 Nielsen and Richelieu 1999). The sensory threshold for the compound can vary depending on the levels of certain wine components, such as sulfur dioxide. It can also be produced as a metabolite of citric acid when all the malic acid has been used up. However, diacetyl rarely taints wine to levels where it becomes undrinkable. 

Other compounds released during autolysis are present in lower amounts, such as lipids and nucleic acids, but could play an important role in the sensorial character of the final wine. Lipids may affect wine flavour in that the fatty acids released could give rise to volatile components with low sensory thresholds, either directly or through derivatives such as esters, ketones and aldehydes (Charpentier and... 

The most significant ketone produced by yeast is diacetyl (2,3-butanedione), a vicinal diketone, although malolactic fermentation is a more important source, when it is used in wine production. Having a sensory threshold of 0.2-2.9 mg/L, according to the type of wine, it is characterised by a nutty , toasty or buttery aroma depending on concentration (Martineau et al. 1995). Dry white wines tend to contain lower concentrations (0.1-2.3 mg/L) than red wines (0-7.5 mg/L) (Bartowsky et al. 2002 Martineau et al. 1995). Acetoin, which produces a buttery flavour, is formed by partial reduction of diacetyl, and is itself reduced to 2,3-butanediol. Acetoin is usually present at concentrations (<80 mg/L) much lower than its sensory threshold of 150 mg/L (Romano and Suzzi 1996). 

The volatile sulfur-containing compounds occurring in wines, while few in number (Rapp has listed 20 26), can be especially problematic for wine quality. As the sensory thresholds for these compounds tend to be quite low, on the order... 

Brettiness". "Volatile phenols can be considered as natural components in wines and beer, or as spoilage compounds when present in excessive amounts" (84). Brettanomyces species can produce both mousiness and, at low concentrations of volatile phenolics, also "a distinct aroma described variously as cider-like, spicy, dove-like or phenolic... formed toward the end of fermentation" (84). The ethyl phenols produced can exceed the sensory threshold 16-fold (85), producing wines, at high concentrations of volatile phenolics, with distinct "barnyard", "stable", and "animal" phenolic odors (85-87). Wines with high concentrations of phenolic odors are deemed "Bretty" by tasters. 

Although over 100 volatiles from finished corks have been reported (2-3), the one component that has been identified 4) as the major cause for cork taint is 2,4,6-trichloroanisole (TCA). In a recent study of Australian wines (5), 100% of the tainted wines, assessed by wine industry personnel, had TCA at or above the sensory threshold. The European QUERCUS study found TCA to be responsible for a musty/moldy taint in at least 80% of cases when it was detected in bottled wines. This makes TCA the most significant impact compound in regard to cork taint, and consequently made it the focus of our analytical developments. 

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