Liberation Profiles of Amino Acids and Oligopeptides during the Enzymatic Digestion of Antarctic Krill (Euphausia superba)

Abstract

Profiles of the time-dependent liberation of free amino acids and oligopeptides during the enzymatic digestions of antarctic krill (autolysis, autolysis in the presence of commercial proteinase and digestion with commercial proteinase alone) were determined by an automatic amino acid analyser and convenient colorimetric methods. Glutamic acid, alanine, valine, leucine, lysine and arginine were preferentially liberated together with oligopeptides by autolysis, while release of glycine and proline was found to be scarce. Autolysis in the presence of commercial proteinase markedly enhanced the accumulation of almost all the amino acids and oligopeptides having the glutamic acid, aspartic acid, glycine and lysine residues. The effect of added enzymes on the profiles of the amino acid liberation was shown to be sinergistic rather than additive, since the digestion with commercial enzyme alone could hardly release free amino acids except for oligopeptides. Taurine, one of the predominant non-protein amino acids in the digest, was kept in constant levels through the digestion periods, indicating that this amino acids may be available for the estimation of product yields in processing. The convenient colorimetric methods consisting of the selective coloration of free amino acids with Cd-ninhydrin and of free amino groups with trinitrobenzenesulfonic acid were proved to be useful for monitoring the digestion process.