Screening of salt taste enhancing dipeptides based on a new strategy using L-amino acid ligase

Many dipeptides have unique physiological functions such as antihypertensive effects and taste enhancing effects. In this study, we focused on the taste of dipeptides and conducted screening for dipeptides as salt taste enhancers. Dipeptides were synthesized using TabS, an L-amino acid ligase (Lal) from Pseudomonas syringae NBRC14081. Six kinds of amino acids, which were easily released by the hydrolysis of proteins or peptides, reacted with 20 proteogenic amino acids, and the reaction mixtures were evaluated using sensory evaluation. In the first screening, the reaction mixture or L-Leu-L-Ser, a known salt taste enhancing dipeptide, was added to a salt solution containing ATP and panelists judged the salt taste intensities. In the second screening, the reaction mixture or residual substrate amino acids was added to a salt solution containing ATP and subjected to sensory evaluation. LMet-Gly was identified as a candidate salt taste enhancer. In addition to sensory evaluation, the salt taste enhancing effect of L-Met-Gly was evaluated using a taste sensor. Taste sensor analysis showed that L-Met-Gly had a salt taste enhancing effect, and the relative sensor response for L-Met-Gly was equal to or higher than that for L-Leu-L-Ser. This is the first report that L-Met-Gly is a salt taste enhancing dipeptide. Furthermore, we propose that the screening method using reaction mixtures of Lal is applicable for the taste evaluation of other dipeptides.