Isolation and Characterization of Neutral Peptides in Soy Sauce

Abstract

A soy sauce sample was fractionated by gel filtration on a Sephadex G–15 column, then the fractions were subfractionated on the basis of acidity by ion exchange chromatography on a QAE-Sephadex A–25 column. After preliminary fractionation, the components in the neutral subfractions were transformed to copper salts, and the salts were chromatographed on a DEAE-Sephadex A–25 column with a borate buffer and aqueous acetic acid to separate neutral peptide substances from a large amount of free amino acids. The peptide fractions were further fractionated on a preparative amino acid analyzer and by paper chromatography to separate the peptide substances.Three glycodipeptides and eight dipeptides were isolated and characterized as the major neutral peptide components in soy sauce. However, it was difficult to anticipate any direct contribution of these peptides to the flavor construction in soy sauce on the basis of their taste intensities and contents.