This study was implemented in order to obtain Tetraplococcus halophilus with the ability to produce umami peptides. A total of 83 strains suspected of being T. halophilus were isolated from 96 naturally fermented soybean paste samples from seven different areas of Liaoning province. Through DNA extraction, 16S rDNA sequencing and comparative homology analysis, 47 of these strains were identified as T. halophilus and were screened for their ability to produce polypeptide, γ-glutamyl transpeptidase and protease and their electronic tongue flavor values. Moreover, factor analysis and factor score comprehensive evaluation were carried out, revealing that T. halophilus LY9-1 had the greatest potential to produce umami peptides. The results of electronic tongue also proved that the fermentation broth of T. halophilus LY9-1 had the highest umami value of 15.05 ± 0.02, as well as protease activity of (85.45 ± 0.03) U/mL, γ-glutamyl transpeptidase activity of (44.23 ± 0.03) U/mL, and polypeptide production of (17.55 ± 0.13) mg/mL. It is speculated that the strain has a strong umami-enhancing potential. The findings reported here can motivate further research on the umami-enhancing mechanism and encourage the industrial application of T. halophilus LY9-1 to enhance the umami of fermented foods.

In order to further analyze the taste characteristics and processing stability of umami peptides from Tetragenococcus halophilus, 41 suspected umami peptides from T. halophilus were tested in this study, and three synthetic peptides (EEEEEE, HAAGMVE, and ESVYAST) with the highest umami values were selected using an electronic tongue. Their taste characteristics were analyzed by sensory evaluation, and the effects of temperature and pH on the stability of the umami peptides were analyzed. The results showed that all three peptides showed umami taste, with perceptual threshold ranging from 0.108 to 0.362 mmol/L. Among them, HAAGMVE demonstrated a particularly potent umami-enhancing effect. The stability analysis results showed that the umami values of EEEEEE, HAAGMVE and ESVYAST increased with increasing pH from 4.0 to 8.0, but remained stable in the temperature range of 25–100 ℃. EEEEEE exhibited the best stability. The results of this study provide a theoretical basis for the development and utilization of umami peptides derived from T. halophilus, and lay a foundation for improving the flavor quality of fermented products and promoting their industrial production.