Increase of “Umami” and “Kokumi” Compounds in Miso, Fermented Soybeans, by the Addition of Bacterial γ-Glutamyltranspeptidase

Thao Van Ho,Hideyuki Suzuki

doi:10.7455/ijfs.v2i1.119

Abstract

γ-Glutamyltranspeptidase (GGT) hydrolyzes γ-glutamyl compounds and transfers their γ-glutamyl moieties to amino acids and peptides. We previously showed that the “umami” taste of soy sauce could be improved by the addition of salt-tolerant Bacillus subtilis GGT to the fermentation mixture, “moromi”. Although miso fermentation is a semi-solid fermentation, unlike soy sauce fermentation, this was also the case. When 15 units of purified B. subtilis GGT were added to 418 g miso “moromi” (fermentation mixture), the glutamate concentration in “moromi” became 20 mM higher and the “umami” taste became stronger than without the addition of GGT after 2 to 6 months of fermentation. In addition, γ-Glu-Val and γ-Glu-Val-Gly, which are known as “kokumi” peptides, were identified in “tamari”, and the concentrations of these γ-glutamyl peptides in “tamari" fermented by the addition of GGT were significantly higher than those of “moromi” without the addition of GGT. These results indicate that B. subtilis GGT is able to improve the taste of miso.

Highlights

Introduction γGlutamyltranspeptidase (GGT; EC 2.3.2.2) consists of one large subunit and one small subunit
We showed that by the addition of salt-tolerant B. subtilis GGT as glutaminase to the fermentation mixture, “moromi”, the glutamate concentration of soy sauce increased and “umami” taste improved (Kijima & Suzuki, 2007)
B. subtilis GGT was purified from the periplasmic fraction of strain CY168 with a Gigapite column and added to miso “moromi”

Summary

Introduction

Introduction γGlutamyltranspeptidase (GGT; EC 2.3.2.2) consists of one large subunit and one small subunit. GGT catalyzes the transfer of γ-glutamyl moiety from γ-glutamyl compounds to amino acids and peptides, and the hydrolysis of γglutamyl compounds (Tate & Meister, 1981). The activated oxygen atom of the side chain of the N-terminal threonine residue of the small subunit of GGT attacks the carbonyl carbon of a γ-glutamyl compound to form a γ-glutamyl enzyme intermediate. When this intermediate is subjected to nucleophilic substitution by amino acids or peptides, the reaction is a transpeptidation reaction, producing new γ-glutamyl compounds. When the intermediate is subjected to nucleophilic attack by water, the reaction is a hydrolysis reaction, releasing glutamate. Soy proteins are cleaved into peptides by proteases from Aspergillus oryzae and/or soyae, and the

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Conclusion