Taste thresholds acids

The importance of lipophilicity to bitterness has been well established, both directly and indirectly. The importance of partitioning effects in bitterness perception has been stressed by Rubin and coworkers, and Gardner demonstrated that the threshold concentration of bitter amino acids and peptides correlates very well with molecular connectivity (which is generally regarded as a steric parameter, but is correlated with the octanol-water partition coefficient ). Studies on the surface pressure in monolayers of lipids from bovine, circumvallate papillae also indicated that there is a very good correlation between the concentration of a bitter compound that is necessary in order to give an increase in the surface pressure with the taste threshold in humans. These results and the observations of others suggested that the ability of bitter compounds to penetrate cell membranes is an important factor in bitterness perception. 

One might suppose on the basis of the amount of attention PTC has received that it is quite a unique substance in its ability to elicit different responses from different individuals. Actually this is not the case at all since wide interindividual differences in taste threshold and taste reactions can be observed with almost anything that can be tasted. Hundred-fold variations in taste thresholds are very common (even when small groups are studied) with respect to substances like sodium or potassium chlorides or hydrochloric acid.41 Saccharine, quinine, cascara, and mannose are among the substances, in addition to creatine mentioned above, for which individuals are known to show highly diverse taste reactions.42 Richter found some children who could not taste 20 per cent sugar solutions.43... 

In summary, although these organic acids are natural honey constituents, the international food legislation prohibits honey additives adulterating its taste. Therefore, the residues of these substances in honey have to remain below their taste threshold [35],... 

The formation of higher alcohols is associated in part with amino acids (90). Higher alcohols or fusel oils may occur as taste components in wines. Taste thresholds of isoamyl alcohol ranged from 100 to 900 ppm (average 300 ppm) in dry white wines for seven panelists (91). 

Monochlorophenols represent an important class of environmental water pollutants of moderate toxicity to mammalian and aquatic life they possess relatively strong organoleptic effects, with taste thresholds of 0.1 pg/L (ppb). Their principal sources are the natural degradation of chlorinated herbicides (e.g., chlorophenoxyacetic acids), chlorination of phenolic substances in waste effluents, and chlorine treatment of drinking water. Of the three chlo-rophenols examined here, 3-chlorophenol exhibited the greatest resistance to sonolysis. 

Table III. Taste thresholds for d-limonene in aqueous solutions containing pectin, acid, and sugar.(24)...

Table 1. Taste, Threshold Value and Discovery of Amino Acids...

Amino acid Taste Threshold value(mg/dl) Where found... 

Using odor activity value (ratio of concentration to odor threshold), Forss et al. (23), Urbach et al. (24), and Stark and co-worker (25-27) reported 5-decalactone, 8-octalactone, decanoic acid, dodecanoic acid, skatole, and indole as important contributors to the flavor of butter oil. In addition, the data of Siek et al. (28) indicated that in fresh butter, the levels of butanoic acid, caproic acid, 5-decalactone were above their taste threshold. 

Flavor enhancers are used imiversally in the food and pharmaceutical industries. Sugar, carboxylic acids (e.g., citric, malic, and tartaric), common salt (NaCl), amino acids, some amino acid derivatives (e.g., monosodium glutamate—MSG), and spices (e.g., peppers) are most often employed. Although extremely effective with proteins and vegetables, MSG has limited use in pharmaceuticals because it is not a sweetener. Citric acid is most frequently used to enhance taste performance of both liquid and solid pharmaceutical products, as well as a variety of foods. Other acidic agents, such as malic and tartaric acids, are also used for flavor enhancement. In oral liquids, these acids contribute unique and complex organoleptic effects, increasing overall flavor quality. Common salt provides similar effects at its taste threshold level in liquid pharmaceuticals. Vanilla, for example, has a delicate bland flavor, which is effectively enhanced by salt. 

IMP and GMP are non-hygroscopic salts. They are stable towards heat (up to 120°C) and acidity (optimum pH is 5-7) [2, 8, 9]. Taste thresholds in aqueous solution are 25-120 ppm and 12-35 ppm for IMP and GMP, respectively [2, 8, 10]. Use of IMP and GMP in liquid foods may present some problems. Many vegetable and animal foods contain phosphomonoesterases which can easily split the phosphomonoester linkage of the ribonucleotides and the flavour improving effect is lost. From a practical standpoint, these enzymes should be inactivated by heating to 85°C before the addition of IMP or GMP. 

Another recent example is the identification of (S)-malic acid 1-0-D-glucopyrano-side, also referred to as Morelid, by the TDA approach [21 ]. It has been isolated from morel mushrooms and identified as a new umami-like tasting compound with a taste threshold of 6 mol/L. A comparative taste profile analysis of a 20 mM aqueous solution of Morelid and a 4 mM aqueous solution of MSG showed similar intensities for the umami-like taste [21], However, the oral evaluation of the glycoside did not show any salty note as compared to MSG. 

Maga, J. A. Taste threshold values for phenolic acids which can influence flavor properties of certain flours, grains and oilseeds. GerealSet Today 1973,18, 326-330. 

This lactone is the flavoring compound formed by the aging of a-ketobutyric acid (Sulser et al., 1967). The flavor is described as malt, molasses, maple, burnt sugar (Chemisis, 1965), with a strong seasoninglike aroma at a concentration of 0.1 ppm and a taste threshold of 1-5 ppb for Sulser et al. (1972). Manley et al. (1980) reported a maple-like, remarkably persistent curry-like odor and wondered if the enolization or the instability of the compound could be responsible for the two notes. It is a potent odorant of roasted powder and brew of arabica coffee with odor descriptions similar to those of G.12, and an odor threshold of 2-4ng/m , air (Blank et al., 1992a,b), of 7.5 ppb in water (Semmelroch et al., 1995). 

The taste threshold of the acid measured by Maga and Lorenz (1973) is 90 ppm in water. 

Comparative sensory studies on the role of alapyridaine in modifying bitter and sour taste perception revealed that neither the threshold concentrations of the bitter compounds L-phenylalanine and caffeine, nor that of the sour tasting citric acid were influenced by the presence of alapyridaine 13). 

Amino acid Q (cal moL ) Taste threshold (mg 100 ml" ) Concentration" in Cheddar Perception" Taste" ... 

Median Taste Thresholds (A/) and Relative (Anhydrous Citric Acid = 100) Amounts to... 

Because these compounds have extremely low taste thresholds and impart a strong toffee, honey or butter-like aroma to beer, considerable attention is paid to controlling their levels. The practices used encourage the breakdown of acetohydroxy acids and the subsequent reduction of diketones to inocuous diols (Chapter 19). 

Taste thresholds for representative compounds are collected in Table 23.2. It should be noted that the concentration of the acids is expressed in normality and percentage whereas other substances are expressed in molarity and... 

Reviewing the primary tastes in beer its sourness will be measured either as its pH (3-8-4-7) or as its titratable acidity. The level of acetic acid reported for normal beers (57-145 ppm) is below the taste threshold (400 ppm) and the same is true of lactic acid (Table 22.7). Infection of beer with microorganisms such as Acetobacter and Lactobacillus spp. may reduce the pH and produce a sour taste. Thus with lambic and gueuze beer the pH may drop to pH 3 2. The level of acetic acid in these beers is 2 6-6-9 times the taste threshold and the level of lactic acid is 5-8-8-6 times its taste threshold [24]. 

The formation of off-flavours in beer has been reviewed [40], Autoxidation of the lipids present in beer produces carbonyl compounds with very low taste thresholds. In particular, linoleic acid is oxidized to trihydroxyoctadecenoic acids (Table 22.7) which break down into 2-/mAz.y-nonenal. This aldehyde and related compounds impart a cardboard flavour to beer at very low concentrations. Other carbonyl are formed from the lipids in beer by irradiation with light including the C9, Cjo, and Cu-alka-2,4-dienals (thresholds 0 5, 0 3 and 0 01 ppb respectively) [40]. The level of diacetyl and pentane-2,3-dione in a range of commercial beers is given in Table 22.11. Quantities in excess of 0 15 ppm impart a buttery flavour more noticeable in lagers than in ales. Bacterial contamination and petite mutants of yeast result in high levels of diacetyl. The sulphur compounds characterized in beer are listed in Table 22.19 with some threshold data. Dimethyl sulphide is the major volatile... 

A major roadblock in identifying gustatory properties of stearic acid is the absence of a delivery system that can present high concentrations or amoimts of hydrophobic stimuli in the absence of tactile (and olfactory) cues. For example, Chale-Rush et al. [4, 22] and Mattes [2] foimd that the detection of smell and taste thresholds of fatty acid stimuli differed with presentation conditions. This absence of a suitable delivery system ciurently limits suprathreshold studies on fatty acid chemosensation in the oral cavity. 

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