Threshold value, taste

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

W. H. Stahl, ed.. Compilation of Odor and Taste Threshold Values Data, DS 48, Amehcan Society for Testing Matehals, Philadelphia, Pa., 1973. 

The corrosive effects to be considered (mainly simple corrosion of metals) are, as would be expected from the edible nature of foodstuffs which are not excessively either acidic or basic but which may contain sulphur, less severe than those often encountered with inedible materials containing reactive substances. The importance of corrosive efiects where foodstuffs are concerned lies not so much in the action of the foodstuffs on the metal involved as in the resultant metal contamination of the foodstuff itself, which may give rise to off-flavours, in the acceleration of other undesirable changes (by the Maillard reaction for example), and in the possible formation of toxic metallic salts. Metal ions generally have threshold values of content for incipient taste effect in different liquid foodstuffs. Except in the case of the manufacture of fruit juices and pickles, process plant failure through corrosion must be rare. Nevertheless all foodstuffs, particularly liquid ones, should be regarded as potentially corrosive and capable of metal pick-up which may be undesirable. 

The human taste threshold for PCP in drinking water is about 30 pg/L (USEPA 1980), a level far below the upper safe limit of 1.01 mg/L and near the no-observable-effect level of 21 pg/L (Table 23.7). Odor detection is not as sensitive as taste the odor threshold for PCP ranges from about 857 pg/L at 30°C, to 1600 pg/L at 20 to 22°C, to 12,000 pg/L at 60°C (USEPA 1980). It is not clear whether the determined organoleptic threshold values made the water undesirable or unfit for consumption (USEPA 1980). If fish and wildlife species of concern have PCP organoleptic thresholds that are similar to those of humans, or lower, will they too avoid contaminated habitats or diets ... 

Fazzalari FA. 1978. ASTM/DS-48A Compilation of odor and taste threshold values. 58... 

API. Review of Published Odor and Taste Threshold Values of Soluble Gasoline Components, API Publication No. 4419 (Washington, DC American Petroleum Institute, 1985). 

Alexander, H.C., McCarty, W.M., and Bartlett, E.A., and Syverud, A.N. Aqueous odor and taste threshold values of industrial chemicals, / Am. Water Works Assoc., 74(ll) 595-599, 1982. 

Some attempts to reduce sodium chloride intake have been carried out. The first is to use some socUum chloride substitutes. Pottasium chloride is widely used for this purpose. However, pottasium chloride is not thought as perfect sodium chloride substitute because it contains bitter taste. Okai and his associates have synthesized several salty peptides (5). These peptides are expected to be good for hypertension, gestosis, diabetes mellitus and other deseases because they contain no sodium ions. These peptides, however, are not expected to be used as sodium chloride substitutes immediately because of the difficulty of in their synthesis and their cost. Although they are struggling to establish a new synthetic method of peptides in a mass production system with reasonable costs and to improve the salty potency of peptides, they have not dissolved this problem. Since the threshold value of ionic taste is around 1 mM regardless their kinds, it seems to be very difficult to prepare an artificial sodium... 

Compound pH before adjusting to 6 Na+/Peptide (mMAnM) Taste Threshold Value (mM)... 

For estimating the contribution of volatile compounds to bread aroma Rothe and coworkers (S) defined "aroma value" as the ratio of the concentration of some volatile compounds to the taste threshold value of the aroma. This concept was further developed by Weurman and coworkers (9) by introducing "odor value", in which aroma solutions were replaced by synthetic mixtures of volatile compounds in water. These mixtures showed the complexity of the volatile fractions of wheat bread, because none of them resembled the aroma of bread. Recently two variations of GC-sniffing were presented (10-11), in which the aroma extract is stepwise diluted with a solvent until no odor is perceived for each volatile compound separately in the GC effluent. The dilution factors obtained indicate the potency of a compound as a contributor to the total aroma. 

Statistical analysis of the aroma and taste threshold values in Table I showed that within 95% confidence limits there was no difference between aroma and taste threshold values for all compounds but four. Octanal and citral had aroma threshold values significantly higher than the corresponding taste threshold values. Nonanal and trans-2-hexenal had higher taste threshold than aroma threshold values. 

Some reported odor threshold values for nootkatone were considerably lower than the taste threshold values. Odor thresholds of 0.8 ppm in water and 30 ppm in air were reported for (+)-nootkatone, the enantiomer of this sesquiterpene ketone present in grapefruit (35). An odor threshold of 0.15 ppm in water was reported for crystalline nootkatone isolated from grapefruit oil (36). In that study, mother liquor from crystallization of nootkatone was 30 times more potent (odor threshold of mother liquor 5 ppb) than nootkatone alone and the panel felt that the aroma of the mother liquor more closely resembled grapefruit aroma... 

Table XI. Taste threshold values for thymol and dimethyl anthranilate in water and in tangerine juice.

These values are usually evaluated through the sense of smell they are marked with O = Odor threshold value. Some values are evaluated through the sense of taste ... 

F = Flavor threshold value, i.e. odor and taste together. 

Stahl, W.H. "Compilation of Odor and Taste Threshold Values Data". ASTM Data Series DS 48, 1973. 

Bitter compounds are also formed in solutions of alanine with xylose and rham-nose.284 Twenty-six HPLC fractions were obtained, seven of which were shown to have high impact on taste dilution analysis. Structures 37-41 accounted for 57% of overall bitterness. The compounds have low threshold values introduction of methyl groups into the furyl rings increase the threshold value. On the contrary, substituting the furyl ring-0 by S (42) lowered the threshold value to almost 104 times lower than that of caffeine on a molar basis. 

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. 

Fig. 3 demonstrates, on the basis of the sweet and bitter taste of the amino acids, that not only hydrophobicity, but also the shape of the side chains influences the threshold value. 

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). 

Determining the threshold value is difficult because subthreshold levels of one compound may affect the threshold levels of another. Also, the flavor quality of a compound may be different at threshold level and at suprathreshold levels. The total range of perception can be divided into units that represent the smallest additional amount that can be perceived. This amount is called just noticeable difference (JND). The whole intensity scale of odor perception covers about 25 JNDs this is similar to the number of JNDs that comprise the scale of taste intensity. Flavor thresholds for some compounds depend on the medium in which the compound is dispersed or dissolved. Patton (1964) found large differences in the threshold values of saturated fatty acids dissolved in water and in oil. 

---