Novel Umami-, Salty-, and Kokumi-Enhancing γ-Glutamyl Tripeptides Synthesized with the Bitter Dipeptides from Defatted Peanut Meal Protein Hydrolysate

Defatted peanut meal protein hydrolysates (DPMHs) usually have a bitter taste gamma-Glutamylation by Bacillus amyloliquefaciens L-glutaminase was introduced to DPMH to reduce its bitterness and generated a gamma-glutamylated product (DPMHG). Extra L-glutamine (L-Gln) (5% w/w) was added to DPMH, and the mixture was then gamma-glutamylated (DPMH-G-Q). Results showed that gamma-glutamylation decreased the bitterness of the products and also enhanced their kokumi, umami, and salty taste, especially for DPMH-G-Q. Bitter amino acids and bitter peptides were found to be substrates (acceptors) of the synthesized.[Glu](1,2)-AAs and gamma-Glu-AA-AAs, respectively. The production yield of gamma-[Glu](1,2)-AAs was only 0.69/100 g for DPMH-G and 2.30/100 g for DPMH-G-Q, which was much lower than that of gamma-Glu-AA-AAs (5.73/100 g for DPMH-G and 18.72/100 g for DPMH-G-Q). The improvement in taste attributes of DPMH might mainly be due to the consumption of bitter dipeptides and the production of gamma-Glu-AA-AAs. In DPMH-G-Q, eight gamma-Glu-AA-AAs were identified, including gamma-Glu-Ile-Lys, gamma-Glu-Ala-Ile, gamma-Glu-LeuLeu, gamma-Glu-Phe-Leu, gamma-Glu-Thr-Leu, gamma-Glu-Ile-Met, gamma-Glu-Val-Leu, and gamma-Glu-Ser-Tyr, which were first time reported. They all can enhance umami, salty, and kokumi taste with a threshold value between 1.61 +/- 0.21-2.16 +/- 0.19, 1.65 +/- 0.19-2.23 +/- 0.20, and 0.67 +/- 0.21-1.00 +/- 0.22 mM, respectively. Insufficient L-Gln restricted the formation of gamma-glutamyl peptides, and this was why DPMH-G had a lower yield and variety than DPMH-G-Q. This also suggested that L-glutaminase is selective to different substrates. Overall, this study provides a new method to reduce the bitterness of protein hydrolysates and also improve the taste by synthesizing gamma-glutamyl tripeptides.

Automated summary

Gamma-glutamylation by Bacillus amyloliquefaciens L-glutaminase was used to reduce the bitterness of defatted peanut meal protein hydrolysates (DPMHs) and generate gamma-glutamylated products (DPMHG). The results showed that gamma-glutamylation decreased the bitterness and enhanced the taste attributes of the products, especially for DPMH-G-Q. This study provides a new method to improve the taste of protein hydrolysates by synthesizing gamma-glutamyl tripeptides.