Bitter peptide

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). 

Today, it is well-known that peptides or proteins exhibit various kinds of taste. Our group has been researching on the relationship between taste and structure of peptides, BPIa (Bitter peptide la, Arg-Gly-Pro-Pro-Phe-Ile-Val) (7 as a bitter peptide, Om-p-Ala-HCl (OBA), Om-Tau-HCl as salty peptides(2j, and "Inverted-Aspartame-Type Sweetener" (Ac-Phe-Lys-OH) as a sweet peptide(5). The relationship between taste and chemical structure was partly made clear. Since commercial demand for these flavor peptides is increasing, we need to develop new synthetic methods which can prepare these peptides in large scale. We developed the following two methods (1) protein recombination method as a chemical method, (2) enzymatic synthesis using chemically modified enzyme as a biochemical method. 

The gross proteolysis of casein is probably due solely to rennet and plasmin activity (O Keeffe et al. 1978). Bacterial proteases and peptides are responsible for subsequent breakdown of the large peptides produced by rennet and plasmin into successively smaller peptides and finally amino acids (O Keeffe et al. 1978). If the relative rate of proteinase activity by rennet, plasmin, and bacterial proteases exceeds that of the bacterial peptidase system, bitterness in the cheese could result. Bitter peptides can be produced from a,-,- or /3-casein by the action of rennet or the activity of bacterial proteinase on /3-casein (Visser et al. 1983). The proteolytic breakdown of /3-casein and the subsequent development of bitterness are strongly retarded by the presence of salt (Fox and Walley 1971 Stadhouders et al. 1983). The principal source of bitter peptides in Gouda cheese is 3-casein, and more particularly the C-terminal region, i.e., 3(193-209) and 3(193-207) (Visser et al. 1983). In model systems, bitter peptides are completely debittered by a peptidases system of S. cremoris (Visser et al. 1983). 

Visser, S., Hup, G., Exterkate, F. A. and Stadhouders, J. 1983. Bitter flavor in cheese. 2. Model studies on the formation and degradation of bitter peptides by proteolytic enzymes from calf rennet, starter cells and starter cell fractions. Neth. Milk Dairy J. 37, 169-180. 

Hamilton, J. S., Hill, R. D. and Van Leeuwen, H. 1974. A bitter peptide from Cheddar cheese. Agr. Biol Chem. 38, 375-379. 

Minamiura, N., Matsumera, Y., Fukumoro, J. and Yamamoto, T. 1972. Bitter peptides in cow milk casein digests with amino acid sequence of a bitter peptide. Agr. Biol Chem. 36, 588-595. 

Sullivan, J. J., Mou, L., Rood, J. I. and Jago, G. R. 1973. The enzymic degradation of bitter peptides by starter streptococci. Aust. J. Dairy Technol. 28, 20-26. Sundman, V. 1953. On the microbiology of Finnish ropy sour milk. 13th Int. Dairy Congr. 3, 1420-1427. 

Bitter peptides have been identified in hydrolyzates of casein (12,13), cheese (13a,b), and soy bean (14,15,15a). The bitter taste has been related to the hydrophobic amino acid content (16-20) and to chain length. Ney and Retzlaff (21) established a formula relating the bitterness of peptides to their amino acid composition and chain length. Too large a proportion of hydro-phobic amino acids gives rise to bitterness yet above a certain molecular weight, bitterness is not perceptible even when there are hydrophobic amino acids (21). Peptides that were responsible for bitterness in Cheddar cheese were rich in Pro, which occurred predominantly in the penultimate position (21a). 

The extraction of hydrophobic peptides is normally performed using organic solvents. Several authors have extracted bitter peptides from cheese using a mixture of chloroform and methanol (2 1) (42-44). 

Bitter peptides Casein hydrolysate Cheese, casein... 

Enzymatic hydrolysates of various proteins have a bitter taste, which may be one of the main drawbacks to their use in food. Arai el al. [90] showed that the bitterness of peptides from soybean protein hydrolysates was reduced by treatment of Aspergillus acid carboxypeptidase from A. saitoi. Significant amounts of free leucine and phenylalanine were liberated by Aspergillus carboxypeptidase from the tetracosapeptide of the peptic hydrolysate of soybean as a compound having a bitter taste. Furthermore, the bitter peptide fractions obtained from peptic hydrolysates of casein, fish protein, and soybean protein were treated with wheat carboxypeptidase W [91], The bitterness of the peptides lessened with an increase in free amino acids. Carboxypeptidase W can eliminate bitter tastes in enzymatic proteins and is commercially available for food processing. 

Arai, S., Yamashita, M., Kato, H., and Fujimaki, M. (1970). Applying proteolytic enzymes on soybean. Part V. A nondialyzable bitter peptide in peptic hydrolyzate of... 

Umetsu, H., Matsuoka, H., and Ichishima, E. (1983). Debittering mechanism of bitter peptides from milk casein by wheat arboxypeptidase. J. Agric. Food Chem., 31, 50-53. 

Degradation of a bitter peptide obtained from the action of Bacillus subtilis on Casein... 

As given in Table XII the Q-method was also successfully applied in the case of bitter peptides from the rennet-sensitive sequence of K-casein (36) ... 

Bitter peptides synthesized acc. to the rennet-sensitive sequence of K-Casein... 

Series of bitter peptides have been isolated from enzymatic hydrolysates of proteins, esp. casein and soybean protein. 

Figure 2 gives the sequence (6 1,62,63.) of ag - casein -which represents about 40 % of casein - and shows the bitter peptides, that have been isolated. According to Mercier (63) the polypeptide chain of casein contains 3 hydrophobic... 

Figure 3 gives the sequence of p-casein - which represents JO % of casein - and the bitter peptides derived from it and isolated by the groups of Clegg (49), Kloster-meyer (46), Gordon (6k). Here also the Q-values of the bitter peptides are above 1400. Please note, that no special single amino acid or sequence is needed to impart the bitter taste. 

From soybean protein hydrolysates several series of bitter peptides have been isolated. As an example Table XIV shows bitter peptides isolated by Fujimaki (69., 70) As before the high Q-values are evident. 

Bitter peptides from peptic soya protein hydrolysates... 

From peptic Zein hydrolysates, Wieser and Belitz (71) isolated bitter peptides which are given in Table XV together with the corresponding high Q-values. 

Regarding the whole picture of enzymatic hydrolysates we came to the conclusion, that certain proteins are more prone to yield bitter peptides than others. Therefore we tried to transfer our method also to proteins as well. This would enable a prediction to be made as to whether in the... 

Figure 2, Bitter peptides from aa,-casein ( ) = hydrophilic regions...

Bitter peptides fron peptic Zein hydrolysates... 

It is interesting to see that proteins with high Q-values above 1400 as e.g. soybean protein, casein wheat gluten, potato protein, Zein are the "parents" of bitter peptides, whereas no bitter peptides have been isolated from hydrolysates prepared from collagen or gelatin, proteins with Q-values below 1300. 

Petrischek (7j0 confirmed that the protein and not the protease is responsible for the occurence of bitter peptides. However, when the "parent" proteins are not bitter but the peptides derived from them are bitter, the questions arise as to why this is so and as to where we must place the molecular weight limits of peptides with Q >1400 that are also not bitter. 

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