Taste compounds

Taste has generally been thought of as a relatively simple sense being composed of salt, sweet, sour, bitter, and umami sensations (Chapter 1). This simplification is not justified since it is clear that each basic taste sensation has many nuances. Furthermore, it is worthwhile to note that each taste sensation supports a different overall flavor perception. For example, if one uses citric acid in a food system, the citrus notes of the flavor will be enhanced. Phosphoric acid is intimately associated with certain cola flavors. Tartaric acid supports grape flavors. Thus, while each acidulant gives a unique sensory character (taste), it also influences our overall flavor perception (interaction to give an overall flavor perception). 

Meat aroma consists of (a) nonvolatile taste substances, (b) taste enhancers and (c) aroma constituents. The latter compounds or their precursors originate essentially from the water-soluhle fraction. The constituents listed in Table 12.22 have been identified as the taste substances of beef broth and roasted meat juice. Solutions of these substances in the given concentrations (Table 12.22) give the typical taste profiles, which are composed of sweet, sour, salty, and glutamate-Uke (umami) notes. The meat note is produced by odorants. 

Dilution analyses were used to elucidate the potent odorants (Table 12.23) of boiled beef and pork and of the meat and skin of fried chicken. Omission experiments (cf. 5.2.7) show that octanak nonanal, (E,E)-2,4-decadienal, methanethiol, methional, 2-furfurylthiol, 2-me-thyl-3-furanthiol, 3-mercapto-2-pentanone and HD3F are the key aroma substances of boiled beef. These compounds are also present in boiled pork and chicken, but species-specific differences 

The aroma of boiled pork is not as intensive as that of beef and the fatty note is more pronounced. The concentrations of the fatty smelling carbonyl compounds, e.g., hexanal, octanal and nonanal, are lower in pork, but in proportion to the concentrations of 2-furfurylthiol, 2-methyl-3-furanthiol and HD3F, they are higher than in beef. This difference appears to favor the intensity of the fatty note in the odor profile of pork. In chicken, the fatty notes become even more noticeable due to 

The aroma of fried chicken is primarily caused by the Strecker aldehydes methyl propanal, 2-and 3-methyl butanal as well as the roast aroma substances 2-acetyl-2- thiazoline, 2-acetyl-1-pyrrohne and the two alkyl pyrazines. The thiazoline and the p3trroline are also formed in lower concentrations during the boiling of meat. 2-Acetyl- 2-thiazoline is the most important roast aroma substance in meat fried for only a few min- 

If beef is heated for a longer period of time, 12-methyltridecanal (MT) appears as an important odorant. Especially in a pot roast, this substance is one of the indispensable aroma substances, which develops its full effect on retronasal detection and increases mouth feeling. The precursors of MT are plasmalogens which occur in the membrane lipids of muscle and slowly hydrolyze on heating (cf. Formula 12.28). 

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Fig. 1. Sweet-tasting compounds of various chemical classes and their common (ah-b) unit, (a) P-D-fmctose (b) saccharin (c) chloroform (d) unsaturated...

Oertly and Myers Auxogluc and Glucophore Components of Sweet-tasting Compounds... 

By identifying the most acidic proton in a number of sweet-tasting compounds, Shallenberger and Acree proposed possible locations for the AH,B systems of these compounds (see Fig. 5). 

A strong curry is generally dark red-brown in colour, whereas a milder curry, such as biryani, is paler in hue. And the difference in the intensity of the curry stain arises from the varying concentration of the coloured components in the curry sauce. As an example, we will discuss the red and spicy tasting compound capsaicin (I), which is the cause of both the hotness of a chilli and contributes to its red colour. 

Stevioside is the most abundant sweet-tasting compound in the leaves. Bridel and Lavielle isolated the crystalline glycoside, stevioside from an alcoholic extract of S. rebaudiana and found it to be 300 times sweeter than... 

Taste. Of the fundamental tastes, bitter is unique in showing human genetic differences in sensitivity. Six decades ago, it was reported tiiat phenylthiocarbamide (PTC) tasted extremely bitter to some individuals while being almost tasteless to others (45). Tlie ability to taste PTC was found to be a dominant genetic trait which occurs across gender, age and culture, with 70% of the American pulation carrying the dominant trait (46). Sensitivity to PTC and propylthiouracil (PROP) are correlated with sensitivities to otiier bitter tasting compounds, such as caffeine, saccharin (after-taste) and salts of i tassium cations and benzoate anions (47,48,49 0). However, in a reexamination of the sensitivity to NaQ and KQ, no differences were found between tasters and nontasters to non-PTC type compounds, and the statistical methods that showed differences were questioned (51). Individuals who do not respond to PTC are not necessarily insensitive to quinine, another intensely bitter compound (49,50,52). 

The current accepted theory suggests that a bitter compound and a sweet compound bind independently at specitic receptors. This situation will be referred to as "independent" in this report. The data to follow will demonstrate that a bitter compound and a sweet compound bind at the same receptor in a competitive manner. Therefore, this situation will be referred to as "competitive" in this report. Which theory was the functioning mechanism of taste reception should be determinable when one measured the taste intensities of mixed solutions of bitter and sweet tasting compounds. In this experiment the mechanism could be predicted to elicit a considerable difference in taste intensity and response that was varying based on the final concentration of each component. The "independent" receptor mechanism would be expected to yield data in which the intensities of bitter and sweet would be unaffected by mixing the two tastes, no matter what the concentration. On the other hand, with the "competitive" receptor mechanism one would expect both flavors to become altered, i.e., one stronger and the other weaker, as component concentrations varied the latter would occur because of competition of the substances for the same site. 

The roasting of foods such as malt or coffee can result in bitter-tasting compounds however, until recently little was known about the chemistry of any compounds formed in the MaiUard reaction that could be responsible for such tastes. Frank et al. [33] identified a new class of compound, l-oxo-2,3-dihydro-lH-indolizinium-6-oxalates, from reaction mixtures containing xylose, rham-nose and alanine (Fig. 12.1). A number of such compounds have been reported and they appear to have low taste thresholds (below 1x10" mmol/L). 

In recent years, non-volatile taste compounds have been becoming more important in the area of modern flavour development. Therefore, the principal approach of the OAV has been adapted for the taste side in the form of the so-called taste-activity value. In order to facilitate the search for taste-active materials and for a better understanding of the taste dimension of foodstuffs, a new instrumental setup called LC-Taste has been developed [58]. 

M.10 The bitter-tasting compound quinine is a component of tonic water and is used as a protection against malaria. When a sample of mass 0.487 g was burned, 1.321 g of carbon dioxide, 0.325 g of water, and 0.0421 g of nitrogen were produced. The molar mass. of quinine is 324 g-mol-1. Determine the empirical and molecular formulas of quinine. 

Sour-tasting compounds are all acidic. The acidity of mineral acids is determined by their hydrogen ion concentration that of organic acids, however, cannot be defined in such simple terms. Thus, a solution of acetic acid tastes more sour than one of a mineral acid at the same pH (5) however, the mineral acid tastes more sour than the organic acid in equimolar solutions. The threshold concentrations of organic acids are pH dependent, yet the relationship is usually quite complicated. The threshold concentrations of formic, malic, and succinic acid increase with increasing pH, whereas those of acetic, butyric, and lactic acid exhibit the opposite trend (7). 

S. Scharbert, N. Holzmann and T. Hofmann, Identification of the astringent taste compounds in black tea infusions by combining instrumental analysis and human bioresponse, J. Agric. Food Chem., 52 (2004) 3498-3508. 

Lee, H.F., Lin, L.C. and Lu, J.R. (1993) Studies on the differences of palatable taste compounds in Taiwan Native chicken and broiler. Journal of the Chinese Agricultural Chemistry Society 31, 605-613. 

Pathogenic bacteria Aeromonas hydrophila, Flavobacter spp., Flexibacter columnaris Odor and taste compounds of microbial origin TT F (Geis et al., 2003)... 

Cocaine was first isolated in 1860 by a chemist named Albert Niemann. Like most organic chemists before and after, Niemann had the habit of tasting compounds that he isolated. On this particular occasion Niemann noted that it caused a numbing of the tongue. Carl Roller, who used it as a topical anesthetic for ophthalmological surgery, first introduced cocaine into clinical practice in 1884. Subsequently, cocaine became popular for its use in infiltration and conduction block anesthesia. 

By now, quite a range of bitter-tasting compounds has been isolated and characterised in Maillard-type reactions. 

In discussing natural taste compounds one faces a dilemma. 

On the one hand almost every compound occurring in nature is a possible taste compound, especially if it is at all water soluble. A vast number of possible taste compounds is thus arrayed before us. On the other hand, relatively few food compounds have been... 

It is known that sweet-tasting compounds are quite common and their chemical structures vary widely. In order to establish a structure-taste relationship, a large number of compounds have been tested, and several molecular theories of sweet taste have been proposed by different groups. At present, the phenomenon of sweet taste seems best explained by the tripartite functioning of the postulated AH, B (proton donor-acceptor) system and hydro-phobic site X (1, 2, J3, 4 5). Sweet-tasting compounds possess the AH-B-X system in the molecules, and the receptor site seems to be also a trifunctional unit similar to the AH-B-X system of the sweet compounds. Sweet taste results from interaction between the receptor site and the sweet unit of the compounds. Space-filling properties are also important as well as the charge and hydro-phobic properties. The hydrophile-hydrophobe balance in a molecule seems to be another important factor. 

L-Asp-L-Cap-OMe (19) was sweet, whereas the ethyl ester (20) was not sweet but bitter, though we could draw the sweet formula (A) to it. This may show that the increased hydrophobicity in the molecule changed the property of the sweet peptide to a bitter property, because it has been known that bitter-tasting compounds are composed of charge and hydrophobic properties. 

Now, I feel I have dwelt too long on the subject of "umami , but the word "umami" in Japanese language sometimes means "sweetness". As to the sweeteners, it is no wonder that such a great deal of work has been done on new sweeteners of natural and artificial origin. Until now, such work has been a kind of hit and miss business. Therefore, the last half of the day was devoted to understanding some of the structural features of molecules that determine their taste properties. Based on the advanced stereo-chemical studies on a large number of sweet and bitter compounds by Dr. Ariyoshi, Dr. Belitz and Dr. Ney, our understanding of the molecular properties of certain taste compounds has advanced markedly. 

The taste receptor mechanism has been more fully described by Kurihara (1987). The process from chemical stimulation to transmitter release is schematically presented in Figure 7-4. The receptor membranes contain voltage-dependent calcium channels. Taste compounds contact the taste cells and depolarize the receptor membrane this depolarization spreads to the synaptic area, activating the voltage-dependent calcium channels. Influx of calcium triggers the release of the transmitter norepinephrine. 

Many investigators have attempted to relate the chemical structure of sweet tasting compounds to the taste effect, and a series of theories have been proposed (Shallenberger 1971). Shallenbeiger and Acree (1967, 1969) pro-... 

Several review articles have described the chemistry of taste and structure-activity relationships.13,14 Two comprehensive reviews have been published in Japan (in Japanese), with particular focus on taste compounds.15,16 However, there has been no recent comprehensive review written from the perspective of natural products chemistry. In this chapter, several taste sensations found in natural products are described along with their structures. Unfortunately, however, it is still very difficult to anticipate the taste quality and intensity from the structure of an organic compound, even for the thoroughly studied sweet and bitter sensations, although some regularity has been observed. It is expected that recent progress in the study of receptors will contribute to a full understanding of the relationship between taste sensation and chemical structure. 

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