Bitterness compounds

Although no consistently effective chemical repellent has been developed for vertebrate pests, some promising materials have been tested as repellents that are based on predator avoidance, specifically compounds from the secretions of predators. In 1995, synthetic sulfur compounds (two thietanes, a thiolane, and a substituted methyl sulfide, which were originally identified from the anal glands of the stoat, ferret, and red fox) suppressed browsing by the introduced AustraUan bmsh-tail opossum in New Zealand about as well as FEP (83). Suggestions were made that these compounds can be made more effective by the use of bitter compounds in a cocktail. 

Just as a multiplicity of hydroxyl groups is normally related to sweetness, multiple nitro groups and the sulfur atom in the —S—S— or —C=S— linkage have been associated with bitter taste. Thus, it was obseiwed that a compound containing three nitro groups, such as picric acid, is usually bitter, and that those with two nitro group may be bitter. Compounds having structure A are also frequently bitter, and it was deduced that the bitterness of the acyl-thiocarbamide class of compounds is due to structure B. 

Taste Threshold of Bitter Compounds, and Equilibrium Constants of Binding of Bitter Compounds by a Bitter-sensitive Protein ... 

Fig. 32.—Fixation of Sweet and Bitter Compounds (Amino Acids) in Rectangular Coor-dinates. ...

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. 

We knew Utetheisa to feed on poisonous plants as a larva (Figure 1B). The plants, of the genus Crotalaria (family Leguminosae), were known to contain pyrrolizidine alkaloids (henceforth abbreviated as PAs), intensely bitter compounds potently hepatotoxic to mammals (7). Other species of Utetheisa were known to sequester PAs (8). We found this to be true for U. ornatrix as well. Adult Utetheisa raised on Crotalaria spectabilis, one of the principal foodplants available to the moth in the United States, contain on average about 700 p,g of monocrotaline (1), the principal PA in that plant (9, 10). 

Cyclo(Leu-Trp), a bitter compound isolated from the fermentation of milk casein by Bacillus subtilis, opened up the field to flavor and fragrance properties. It was further noted that dipeptides became more bitter when blockage of both the amino and carboxyl groups occurred or the dipeptide was converted into a DKP. This phenomenon opened the field of taste exhibition. ... 

Bar-Peled M, Lewinsohn E, Fluhr R, Gressel J (1991) UDP-rhamnose flavanone-7-0-glucoside-2"-0-rhamnosyltransferase purification and characterization of an enzyme catalyzing the production of bitter compounds in Citrus. J Biol Chem 266 20953-20959... 

Nolte, D. L., Mason, J. R., and Lewis, S. L. (1994a). Tolerance of bitter compounds by an herbivore, Caviaporcellus. Journal of ChemicalEcology 20,303-308. 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

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). 

Sweetness Production by the Combination of Bitter and Sweet Tastes. Sensory tests using typically bitter compounds such as brucine, strychnine, phenylfiiiourea, caffeine and bitter peptides were performed. Sensory tests using typically bitter compounds such as brucine, strychnine, phenylthiourea, caffeine and bitter peptides were performed. Sensory taste impression were also measured for combinations of acetic acid (sour) and typical bitter compounds (5). The data from these studies indicated that the tastes of ese bitter/sour mixtures changed to a sweet taste regardless of their chemical structure of the bitter component (Table II). 

Table II. Tasting Behavior of Combination of Typical Bitter Compounds and Acetic Acid ------------------------------------5------------...

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. 

Theoretical sensory sweetness and bitterness scores for the two theories are described below for mixed solutions of sweet and sour. This exercise considers the case of a mixture of 20 mM D-phenylalanine (D-PA) and 60 mM L-phenylalanine (L-PA). Individually each of these solutions yield a sensory score of 5.0, i.e. the sweetness of 30 mM D-PA is 5 and the bitterness score of 60 mM L-PA is 5. Theoretically, if both compounds bind independendy at different taste receptors, the sweetness and bitterness should each be 5. On the oAer hand, if both compound bind at the same taste receptor in a competitive manner, die sweetness and bitterness scores should decrcase. In regards to the latter, the sweet and bitter compound were mixed in a ration of 1 3 (20 mM to 60 mM) which yields a probability of fitting a taste receptor of l-in-4 for sweet and 3-in-4 for bitter. If these probabilities are multiplied by the original concentrations, i.e. 20 mM and 60 mM, the products would be in the expected concentration of 5 mM (1/4 of 20mM) and 45 mM (3/4 of 60mM). The sweetness of a 5 mM solution and the bitterness of a 45 mM solution corresponds to a sensory score of 2 and 3, respectively, and represent the expected sensory score for the competitive hypothesis. 

Table V. Tasting Behavior of Combination of Typical Bitter Compounds and Benzoyl-e-aminocoproic acid...

Design of bitter compounds seems to be useless. However, it should give us not only some idea when we study the taste tetrahedron, but much useful information when we... 

Benzoyl-e-aminocaproic acid-bitter compound mixtures, tasting behavior, 33,34f... 

Since no bitter compounds are reported, the A value in Eq. 50 is the net sweet intensity relative to sucrose. The nitro and cyano groups seem to play an identical role and the substituent effects are common in these two series of compounds. 

H Goldstein, P Ting. Post-kettle bittering compounds Analysis, taste, foam and light stability. EBC Symposium on Hops, 1994, pp 141-153. 

Edwards, J. and Kosikowski, F. V. (1983). Bitter compounds from Cheddar cheese. 1. Dairy Sci. 66, 727-734. 

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