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. Here I think some remarks on hydrophobic interactions (1) would be appropriate. It is generally accepted now, that hydrophobic interactions are a contributing factor to protein behaviour and esp. to the formation of the secondary structure, e.g. helix. This means, that as shown in Figure 1 hydrophobic residues of the amino acids in a peptide are driven together by clusters of water molecules and so the secondary structure of a peptide or protein is formed. For the transfer from the helical to the stretched form, Tanford (2) found that the transfer free energy of the total protein results from the sum of the contributions of the single amino acid residues. The Δf values of the