New Method To Produce Kokumi Seasoning from Protein Hydrolysates Using Bacterial Enzymes

In the present study, we demonstrate a novel use for a commercially available glutaminase that can be used as a γ-glutamyltranspeptidase in kokumi seasoning production. Soy protein and gluten were hydrolyzed using a protease isolated from Bacillus licheniformis. The resulting protein hydrolysates were γ-glutamylated with a γ-glutamyltranspeptidase, which is sold as a glutaminase from Bacillus amyloliquefaciens, to produce kokumi seasonings. For γ-glutamylation of soy protein hydrolysate, glutamine was added to the reaction mixture. On the other hand, reaction conditions for enzymatic proteolysis were optimized to liberate glutamine from gluten in large amounts, and the addition of glutamine was not required for γ-glutamylation of gluten hydrolysate. The soy protein and gluten hydrolysates as well as their γ-glutamylated products were subjected to taste evaluation. Soy protein hydrolysates were bitter. Although γ-glutamylation significantly reduced bitterness, the taste was still considered unfavorable. γ-Glutamylated gluten hydrolysate is the most preferable sample and had significantly enhanced thickness, kokumi, and umami tastes, with a moderate increase in saltiness.