Tripeptides taste

Re-formation of the Taste of BMP. According to the above results, the taste of BMP might produced by the combination of the basic amino acid (Lys) at N-terminal and acidic amino acids at the middle part. To confrnn this idea, we prepared a mixed solution of the N-terminal dipeptide (Lys-Gly), the acidic tripeptide at the middle part (Asp-Glu-Glu) and C-terminal tripeptide (Ser-Leu-Ala) and examined the taste. We also studied tastes of a mixture in which a basic dipeptide fragment was replaced by Orn-p-Ala, a salty dipeptide, and a mixture in which Glu-Glu replaced an acidic tripeptide fragment. The result are shown in Table XIV. All of the combinations produced the same character of the taste as BMP. It means that the taste of BMP is mainly produced by the combined effect of the N-terminus basic dipeptide and the acidic tripeptide of the middle part. However, taste strength of the mixture became... 

Otagiri et al. (22) used model peptides composed of arginine, proline, and phenylalanine to ascertain the relationship between bitter flavor and chemical structure. They reported that the presence of the hydrophobic amino acid at the C terminus and the basic amino acid at the N terminus brought about an increase in the bitterness of di- and tripeptides. They further noted a strong bitter taste when arginine was located next to proline and a synergistic effect in the peptides (Arg)r(Pro) ,-(Phe) (/ = 1,2 m, n = 1, 3) as the number of amino acids increased. Birch and Kemp (23) related the apparent specific volume of amino acids to taste. 

After the finding of a sweet taste in L-Asp-L-Phe-OMe (aspartame) by Mazur et at. (6), a number of aspartyl dipeptide esters were synthesized by several groups in order to deduce structure-taste relationships, and to obtain potent sweet peptides. In the case of the peptides, the configuration and the conformation of the molecule are important in connection with the space-filling properties. The preferred conformations of amino acids can be shown by application of the extended Hiickel theory calculation. However, projection of reasonable conformations for di- and tripeptide molecules is not easily accomplished. 

Further examinations of the molecular features and of the model of receptor have suggested that several aspartyl tripeptide esters may also taste sweet. In confirmation of the idea, several tripeptide esters have been synthesized. In the first place, L-Asp-Gly-Gly-OMe (38) was synthesized as an arbitrarily-selected standard of tripeptides, because it was considered that this peptide ester had the simplest structure, and correlation of other peptides to (38) was easy. The tripeptide ester was predicted that it would be slightly sweet or tasteless because its projection formula was similar in size and shape to that of L-Asp-Gly-0Bum which is 13 times sweeter than sucrose (16) and because it is more hydrophilic than the dipeptide. The tripeptide (38) was devoid of sweetness and almost tasteless. 

Finally, L-Asp-D-Val-Gly-OMe (41) was synthesized in order to see whether it remained sweet. The peptide was devoid of sweetness and almost tasteless, though D-valine-containing aspartyl dipeptide esters such as L-Asp-D-Val-0Pr (17) and L-Asp-D-Val-OPrt (8, 17), which are similar to the tripeptide ester in size and shape and have potent sweet taste. 

Up to this point only amino acids, di- and tripeptides had been considered. However, we wanted to see if the Q-concept could be extended to higher peptides as well. Stepwise we synthesized a heptapeptide and followed the change of the taste. The following Table VIII shows this synthesis... 

It was reported that q-glut amyl peptides, particularly peptides with hydrophilic amino acids, such as Glu—Asp, Glu-Thr, Glu-Ser, and Glu-Glu, elicited an umami flavor236 These peptides were isolated from the umami constituents in the enzymatically hydrolyzed products of soybean proteins. The same author also reported that tripeptides such as Glu-Gly-Ser also elicited the umami taste. The threshold value (0.15%) of these peptides is greater than that of MSG. The flavor of meat extract can be reproduced using these peptides with MSG and IMP. Recently,. Y-lacroyl glutamic acid, which is a condensation product of lactic acid with glutamic acid, was shown to elicit a weak umami taste, similar to MSG.237... 

The contribution of the d enantiomers to the characteristic taste of foods is currently being evaluated, but it is clear that the d enantiomers generally taste sweeter , or at least less bitter , than do their l isomers. Of course, kitchen preparation can involve many subtle chemical changes that enhance the attractiveness of natural foodstuffs, including racemisation (Man and Bada, 1987) therefore d enantiomers may be introduced in this way. Peptides are taste contributors, for example the bitter-tasting dipeptides Trp—Phe and Trp—Pro and the tripeptide Leu—Pro—Trp that are formed in beer yeast residues (Matsusita and Ozaki, 1993). 

Thr, Glu-Gly, Glu-Ser, Ala-Glu, Gly-Glu, Gly-Glu-Gly, Glu-Glu, and Glu-Asp were found. These polar peptides were reported to elicit a savory umami taste [7,27-29]. Frerot and coworkers [30] identified small peptides in Parmesan cheese. They observed that tripeptides such as Glu-Leu-Glu or Glu-Asp-Phe consisting of a hydrophobic amino acid residue and at least one acidic and one either acidic or hydrophilic amino acid residue impart mouthfeel and umami taste to foods and could replace MSG to some extent. Van den Oord and van Wassenaar [31], however, discuss glutamyl di- and tripeptides controversially and generally question the existence of glutamate-like-tasting peptides. 

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