Bitter-tasting sake peptides derived from the N-terminus of the rice glutelin acidic subunit

Abstract

Five bitter-tasting peptides were isolated from charcoal-untreated sake, following a Sepabeads resin separation, an initial reverse-phase chromatography (RP-HPLC), a gel permeation-chromatography, and a second RP-HPLC. The isolated peptides consisted of six to thirteen amino acid residues. The N-termini were uniformly pyroglutamate residues. Based on the rice protein database, the peptides were derived from two different N-termini of the rice glutelin acidic subunit. One of them was reported as a prolyl endopeptidase inhibitor. The thirteen amino acid peptides in charcoal-untreated ginjyo-type sakes were lower than that in charcoal-untreated jyunmai-type sakes. The thirteen amino acid peptides were not detected in the commercial ordinary-type sake analyzed. The concentration of analyzed peptides of nine to thirteen amino acid residues in charcoal-untreated sake exceeded their preliminary estimated sensory threshold values, suggesting that they contribute to the sensory quality of charcoal-untreated sake.