Bitterness of peptides

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). 

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. 

Bitterness of Peptides Amino Acid Composition and Chain Length... 

During our work on taste of foods we synthesized a series of peptides and soon came to the opinion, that the bitterness of peptides is caused by the hydrophobic action of amino acid side chains. 

In Table XIII we have collated other former postulates for bitterness of peptides. The results are in agreement with the Q-rule for example the sequence Gly-Pro-Pro-Phe postulated by Minamiura ( 4) to be the core of the bitterness has a high Q-value of 1963. 

Ve studied the influence of chain length on the bitterness of peptides by gel permeation chromatography of... 

Ney, K.H. 1971. Bitterness of peptides amino acids composition and chain length In Food Taste Chemistry , Advances in Chemistry Series 115 (J.C. Boudreau ed.), pp. 149-173, American Chemical Society, Washington, DC. 

Ney, K.H. and RezzlafF, G. 1986. A computer program predicting the bitterness of peptides, especially in protein hydrolysates, based on amino acid composition and chain length (computer Q) In Shelf Life of Foods and Beverages , Proceedings of the 4th International Flavour Conference (G. Charalambous ed.), pp. 543-550. Elsevier, The Netherlands. 

Source. Reprinted with permission from K.H. Ney, Bitterness of Peptides Amino Acid Composition and Chain Length, in Food Taste Chemistry, J.C. Boudreau, ed., ACS Symp. Ser. 115, 1979, American Chemical Society. 

Almost all peptides of hydrophobic L-amino acids elicit a bitter taste, which indicates that the bitterness of peptides is caused by the hydrophobic property of the amino acid side chain. Ney (12) has reported that whether a peptide has a bitter taste or not depends on its hydrophobic value Q. The value Q is obtained by adding the Af-values (Table 3) of each constituent amino acid residue of a peptide and dividing the sum by the number of amino acid residues (n). 

It has been demonstrated that CPase Top enzyme is useful for eliminating bitterness originating from soy protein and com gluten. With respect to the bitterness from casein, although the bitterness was not completely eliminated, it was effective in reducing most of the bitterness. It is postulated that the bitterness of peptides is due to the hydrophobic amino acids in the C-terminus position (4). This assumption is necessary for the elimination of bitterness by liberating a hydrophobic amino acid at the C-terminus by the substrate specificity of CPase Top. 

Ney, K. H. (1979b). Bitterness of peptides Amino acid composition and chain length. ACS Symp. Ser. 115, 149-173. 

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