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Umami is an important element affecting food taste, and the development of umami peptides is a topic of interest in food-flavoring research. The existing technology used for traditional screening of umami peptides is time-consuming and labor-intensive, making it difficult to meet the requirements of high-throughput screening, which limits the rapid development of umami peptides. The difficulty in performing a standard measurement of umami intensity is another problem that restricts the development of umami peptides. The existing methods are not sensitive and specific, making it difficult to achieve a standard evaluation of umami taste. This review summarizes the umami receptors and umami peptides, focusing on the problems restricting the development of umami peptides, high-throughput screening, and establishment of evaluation standards. The rapid screening of umami peptides was realized based on molecular docking technology and a machine learning method, and the standard evaluation of umami could be realized with a bionic taste sensor. The progress of rapid screening and evaluation methods significantly promotes the study of umami peptides and increases its application in the seasoning industry.

To shorten the complex and tedious process of traditional umami peptide identification, a novel model based on common feature pharmacophore (HipHop, a ligand molecule-based screening method) and molecular docking (a receptor protein-based screening method) was established for umami peptide screening. In this study, HipHop was used to perform a preliminary screening of peptides. Dipeptides with potential umami activity were docked into the umami taste receptor T1R1/T1R3 for a second screening. Twenty previously unreported umami dipeptides identified through virtual screening were validated using sensory evaluation and electronic tongue analysis. All 20 dipeptides (HE, HD, KE, EH, ET, EQ, DH, DR, DQ, DN, DY, DM, DI, DV, QE, QD, NE, ND, CE, and SE) had umami taste with umami threshold values ranging from 0.094 to 1.517 mmol/L. Therefore, when we increased the screening criteria for docking energy to -60 kcal/mol, the virtual screening results had 100% accuracy. The T1R1-peptide complexes of the four dipeptides with the lowest umami threshold values were subjected to molecular dynamics (MD) simulations for 100 ns, and the results showed that the four umami dipeptides remained in the starting active cavity. Overall, this screening strategy could be applied to the rapid screening of umami peptides in food products.

Umami peptides can help reduce the salt content in foods while still maintaining a savory taste. Few studies have reported the bioactivity of umami peptides after consumption. We studied the bioactivities of 12 umami peptides after gastrointestinal digestion. Three umami peptides exhibited angiotensin I-converting enzyme (ACE) inhibitory and antioxidant activity after digestion. Six novel peptides were identified from digestion solutions of the peptides by HPLC-MS/MS. Among them, CC, CCNK, and HCHT had both ACE inhibitory activity (IC50 values were 9.81, 9.00, and 114.99 μM, respectively) and antioxidant activity (strong 1,1-Diphenyl-2-pycryl-hydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) free radical scavenging activities). AHSVRF had strong ACE inhibitory activity. These peptides increased the nitric oxide concentration and decreased the content of endothelin-1 in a medium of human umbilical vein endothelial cells in a dose-dependent manner. Experiments with damaged HepG2 cells showed that peptides CC, CCNK, and HCHT had antioxidant activity through their cytoprotective effects and by reducing the reactive oxygen species content. The results indicated that umami peptides may provide many health benefits after consumption.

Umami peptides have been the focus of umami studies in recent years because of their high nutritional value and flavor activity. However, the existing screening methods of umami peptides were cumbersome, complex, time-consuming and laborious, and it was difficult to achieve high-throughput screening. In this study, a novel umami peptide rapid screening model was designed and by using lamb bone aqueous extract as raw material, through the step-by-step screening of peptidomics, machine learning methods, and molecular docking technology. Results showed that six novel peptides about lamb bones were obtained, which verified the feasibility of the model and could be used for high-throughput screening of umami peptides. Results of molecular docking between umami peptide and T1R3 subunit revealed that the main interaction forces were hydrogen bonding and electrostatic interaction, and the key binding sites were GLU277 and SER146. It provides the basis for studying the binding mechanism of umami peptide.

To explore the saltiness enhancement effect and mechanism of umami peptides, umami peptides from Ruditapes philippinarum and ham were mixed with NaCl and determined using electronic tongue, sensory evaluation, and the aroma chicken model (ACM), then transmembrane channel-like protein 4(TMC4) receptor was constructed for molecular docking. The results showed that KEMQKN, NGKET, RGEPNND, AHSVRFY, LSERYP, NRTF, TYLPVH, EV, AGAGPTP, and GPAGPAGPR had saltiness enhancement effect, which could be increased to 0.4-0.6 % NaCl salty taste in 0.3 % NaCl. Under neutral conditions (pH6.5), most umami peptides were in negative ion state which may be the main reason that umami peptides could bind to the TMC4 receptor and enhance saltiness. The lowest docking energy was -113.325 kcal/mol among 10 peptides and the active sites Lys568, Trp145, Tyr565, Arg151, and Gln155 in TMC4 may play a key role. Thus, this study provides basic theory and data for salt-reduction strategies.

To understand the taste of the Ruditapes philippinarum, 14 novel umami peptides were isolated and identified by gel chromatography, HPLC and UPLC-ESI-QTOF-MS/MS. Separations were combined with sensory evaluations and electronic tongue determinations. The peptide sequences were GRVSNCAA, SEEK, KEMQKN, KSAEN, QIEELEGK, TDVEQEGD, HNESQN, RGEPNND, TGDPEK, KGGGGP, TYLPVH, PAATIPE, GPAGPAGPR and AGAGPTP. All peptides had umami and umami-enhancing qualities, KSAEN and QIEELEGK had higher sensory evaluation than the others, while PAATIPE and HNESQN had the best umami-enhancing taste in a 0.35% MSG solution. Molecular docking of the peptides with T1R1/T1R3 indicated that Ser123, Ser146 and Tyr143 may be important in the interaction of the peptides with T1R3. Arg303, Ser123 and Asp166 appear to be involved in the synergistic effect of umami peptides combined with monosodium glutamate. The omission test and the addition test confirmed that the 14 umami peptides contributed to the umami taste of R. philippinarum.

Peptides are critical to the taste of dry-cured ham. To isolate and identify umami peptide fractions from the water-soluble extractions (WSEs) of Jinhua and Parma hams, separation procedures utilizing Sephadex G-25 and reversed-phase high-performance liquid chromatography (RP-HPLC) were combined with sensory evaluations (taste dilution analysis and an electronic tongue). The amino acid sequences of the umami peptides, Cys-Cys-Asn-Lys-Ser-Val (CCNKSV) from Jinhua ham and Ala-His-Ser-Val-Arg-Phe-Tyr (AHSVRFY) from Parma ham, were identified by MALDI-TOF-MS; subsequently, both were synthesized, and their umami taste properties were evaluated. The results indicate that the tastes of the umami peptides were similar to those of the hams' WSEs.