The adsorption isotherms of some dipeptides composed of un-ionizable side chains were measured at 25'C in a single component system, and all of them obeyed the Langnnuir equation. The parameters obtained at pH 7 could be roughly correlated with the hydrophobic and steric parameters of constituent amino acids. To find a method for predicting the amount of dipeptide adsorbed under various conditions, the applicability of the Polanyi adsorption potential theory was examined. The amount of dipeptide adsorbed could be roughly estimated from the adsorption isotherms of the amino acids, although the estimation lacked strictness in a physical sense.Keywords: adsorption, dipeptide, activated carbon Attention has been paid to the utilization of protein hydrolysate as a food seasoning (Ueno et at, 1990) and foaming agent (Nagatomo et al, 1990). In these applications, a separation process is incorporated to obtain a peptide mixture with a specific functionality. An infusion solution rich in branched amino acids and poor in aromatic ones is useful as a nutrient for patients with liver diseases (Fischer et al, 1976). A peptide mixture with such an amino acid composition would be more promising than an amino acid mixture because of its faster absorption in the intestine and lower osmotic pressure. We reported the preparation of a peptide mixture with a high Fischer ratio, which is the ratio of branched amino acids to aromatic ones, from the enzymatic hydrolysate of casein using gel chromatographic resin (Adachi et al, 1991) or activated carbon (Adachi et al, 1993). The preparation of a peptide mixture rich in aromatic amino acids from a protein hydrolysate was also attempted (Li et al, 1985). Thus, peptides with a definite composition would be useful as foodstuffs.To reasonably design an adsorptive separation of peptides, knowledge of their adsorption equilibria and rate processes is required. A protein hydrolysate includes many kinds of peptides. It would be difficult to predict the adsorption isotherm of each peptide onto an adsorbent in a multi-component system. As the first step in the adsorptive separation design of peptides from protein hydrolysate, we measured the adsorption isotherms of some dipeptides composed of amino acids having un-ionizable side chains onto an activated carbon in a single component system, and the methods to predict them are discussed.
Materials and MethodsMaterials Glycyl-L-isoleucine (Gly-Ile), glycyl-L-leucine (Gly-Leu), glycyl-L-phenylalanine (Gly-Phe), glycyl-L-tryptophan (Gly-Trp), glycyl-L-tyrosine (Gly-Tyr), L-leucyl-L-leucine (Leu-Leu), L-leucyl-L-tyrosine (Leu-Tyr) and L-phenylalanyl-L-leucine (Phe-Leu) were purchased from Sigma(Ser-Leu) were obtained from Kokusan Chemical Works, Osaka. Glycylglycine (Gly-Gly) and most ofthe amino acids used were purchased from Wako Pure Chemical Industries, Osaka. L-Tryptophan and L-tyrosine were products of the Peptide Institute, Osaka. Other chemicals were purchased from Nacalai Tesque or Wako Pure Chemical Industries and were of analytical grade.Th...