New insight into umami receptor, umami/umami-enhancing peptides and their derivatives: A review

Antihypertensive Effect, ACE Inhibitory Activity, and Stability of Umami Peptides from Yeast Extract

Bioactive peptides from foods have garnered considerable attention as viable supplements for hypertensive patients. Herein, the antihypertensive effect and mechanism of umami peptides from yeast extract were investigated based on the pharmacophore model, simulated digestion, spontaneously hypertensive rat (SHR) model, and molecular docking. Notably, umami peptide LLLLPKP exhibited favorable angiotensin I-converting enzyme (ACE) inhibitory activity (IC50 = 10.22 μM) in vitro and regulated blood pressure in the SHR model with excellent durability. Remarkably, LLLLPKP showed the highest Fitvalue (4.022) of the pharmacophore model, indicating its similar pharmacological effects as ACE inhibitors. During the simulated gastrointestinal digestion, the ACE inhibition rate of LLLLPKP was merely reduced by 5.89%, but it was enzymatically cleaved into 14 peptide segments. The C-terminal sequence comprising L (4), P (5), K (6), and P (7) exhibited robust stability and a notable presence within the peptide segments postdigestion. Meanwhile, according to molecular docking, these four residues within LLLLPKP were responsible for all interactions with key sites within active pockets S1 and S2 and the active pocket of Zn2+. In light of these findings, LLLLPKP is a highly promising antihypertensive peptide. Developing this umami peptide with antihypertensive effects holds substantial importance for the long-term treatment of hypertension.

Umami taste evaluation based on a novel mouse taste receptor cell-based biosensor

Umami, a taste sensation known for its savory and delicious properties, has garnered considerable attention from both consumers and the food industry. However, current understanding and evaluation of umami characteristics remain limited, presenting a long-standing issue. To address this challenge, we have developed a self-assembled biosensor based on matured taste receptor cells (TRCs), obtained through isolation and culture of taste stem cells. TRCs, as the recognition element, were mounted onto the surface of a glassy carbon electrode (GCE) treated with gold nanoparticles (AuNPs) and poly-L-lysine (PLL). Key parameters including the cell incubation time and concentration were optimized to ensure the optimal performance of the TRCs-based biosensor. AuNPs were deposited onto the GCE surface via 90 s electrochemical reduction. TRCs concentration of 106 cells/mL and incubation time of 12 h were chosen by electrochemical characterization. Using this novel, rapid, and sensitive TRCs-based biosensor, we successfully detected L-monosodium glutamate (MSG) and other umami substances, demonstrating a good linear relationship within the range of 10-9 - 10-5 M between response signals and concentration of MSG stimuli. Our results provide insights into taste signal transduction mechanisms and suggest the potential for biomimetic sensors in intelligent perception applications.

Umami-BERT: An interpretable BERT-based model for umami peptides prediction

Umami peptides have received extensive attention due to their ability to enhance flavors and provide nutritional benefits. The increasing demand for novel umami peptides and the vast number of peptides present in food call for more efficient methods to screen umami peptides, and further exploration is necessary. Therefore, the purpose of this study is to develop deep learning (DL) model to realize rapid screening of umami peptides. The Umami-BERT model was devised utilizing a novel two-stage training strategy with Bidirectional Encoder Representations from Transformers (BERT) and the inception network. In the pre-training stage, attention mechanisms were implemented on a large amount of bioactive peptides sequences to acquire high-dimensional generalized features. In the re-training stage, umami peptide prediction was carried out on UMP789 dataset, which is developed through the latest research. The model achieved the performance with an accuracy (ACC) of 93.23% and MCC of 0.78 on the balanced dataset, as well as an ACC of 95.00% and MCC of 0.85 on the unbalanced dataset. The results demonstrated that Umami-BERT could predict umami peptides directly from their amino acid sequences and exceeded the performance of other models. Furthermore, Umami-BERT enabled the analysis of attention pattern learned by Umami-BERT model. The amino acids Alanine (A), Cysteine (C), Aspartate (D), and Glutamicacid (E) were found to be the most significant contributors to umami peptides. Additionally, the patterns of summarized umami peptides involving A, C, D, and E were analyzed based on the learned attention weights. Consequently, Umami-BERT exhibited great potential in the large-scale screening of candidate peptides and offers novel insight for the further exploration of umami peptides.

Identification of umami peptides from Wuding chicken by Nano-HPLC-MS/MS and insights into the umami taste mechanisms

Wuding chicken is popular with consumers in China because of its umami taste. This study aimed to identify novel umami peptides from Wuding chicken and explore the taste mechanism of umami peptides. The molecular masses and amino acid compositions of peptides in Wuding chicken were identified by nano-scale liquid chromatography-tandem mass spectrometry (Nano-HPLC-MS/MS). The taste characteristics of the peptides synthesized by the solid-phase method were evaluated by sensory evaluation combined with electronic tongue technology. The secondary structure of the peptides was further analyzed by circular dichroism (CD), and the relationship between the structure and taste of the peptides was elucidated by molecular docking. The results showed that eight potential umami peptides were identified, among which FVT (FT-3), LDF (LF-3), and DLAGRDLTDYLMKIL (DL-15) had distinct umami tastes, and FT-3 had the highest umami intensity, followed by LF-3 and DL-15. The relative contents of β-sheets in the three umami peptides were 55.20%, 57.30%, and 47.70%, respectively, which were the key components of Wuding chicken umami peptides. In addition to LF-3 embedded in the cavity-binding domain of the TIR1, both FT-3 and DL-15 were embedded in the venus flytrap domain (VFTD) of the T1R3 to bind the umami receptor T1R1/T1R3. The main binding forces between the umami peptides and the umami receptor T1R1/T1R3 relied on hydrogen bonds and hydrophobic interactions, and the key amino acid residues of the combination of umami peptides and the umami receptor T1R1/T1R3 were Glu292, Asn235, and Tyr262.

Identification and Characterization of Novel Umami Peptides from Protein Hydrolysates of Morchella esculenta and Their Interaction with T1R1/T1R3 Receptor

The study aimed to explore umami peptides derived from protein hydrolysates of Morchella esculenta. According to the electronic tongue and sensory evaluation, the ultrafiltration fractions (<3 kDa) of the protein hydrolysates exhibited the strongest umami taste. The overall flavor of the screened fractions was significantly improved after the Maillard reaction, based on the electronic nose and electronic tongue analyses, and the content of total free amino acid increased from 387.35 to 589.30 μg/mL. A total of 37 peptides with high confidence were identified from the fractions using LC-MS/MS. Additionally, two novel umami peptides were screened through bioinformatics and molecular docking, and their recognition threshold was 0.43 (EYPPLGRFA) and 0.52 mmol/L (TVIDAPGHRDFI), respectively. In addition, molecular docking analysis revealed that the key binding sites, such as Ser148, Leu51, Arg327, and Leu468 in T1R1/T1R3 contributed to docking, and hydrogen bonding and hydrophobic interactions were the dominant interaction forces between the two umami peptides and T1R1/T1R3 receptor. This study contributes to the development and utilization of Morchella esculenta in flavored foods.

Identifying Umami Peptides Specific to the T1R1/T1R3 Receptor via Phage Display

Umami peptides are small molecular weight oligopeptides that play a role in umami taste attributes. However, the identification of umami peptides is easily limited by environmental conditions, and the abundant source and high chromatographic separation efficiency remain difficult. Herein, we report a robust strategy based on a phage random linear heptapeptide library that targets the T1R1-Venus flytrap domain (T1R1-VFT). Two candidate peptides (MTLERPW and MNLHLSF) were readily identified with high affinity for T1R1-VFT binding (KD of MW-7 and MF-7 were 790 and 630 nM, respectively). The two peptides exhibited umami taste and significantly enhanced the umami intensity when added to the monosodium glutamate solution. Overall, this strategy shows that umami peptides could be developed via phage display technology for the first time. The phage display platform has a promising application to discover other taste peptides with affinity for taste receptors of interest and has more room for improvement in the future.

Cooperative combination of non-targeted metabolomics and targeted taste analysis for elucidating the taste metabolite profile and pathways of traditional fermented golden pompano

Fermentation plays a key role in taste formation in traditional fermented golden pompano and involves a series of complex metabolic reactions. Indeed, the taste profile of fermented golden pompano exhibits remarkable variation during early fermentation. Herein, nutritional fingerprinting (proteins, amino acids, lipids, etc.) was applied to discriminate the various biomolecular changes involved in golden pompano fermentation. Among the differential metabolites, amino acids, small peptides, lipids, and nucleotides were considered taste-related compounds. An increase in the amino acid content was observed during fermentation, while the peptide content decreased. Glutamic acid, alanine, and lysine had the highest taste activity values and were the main contributors to taste formation. Metabolic pathway enrichment analysis revealed that taste formation was primarily associated with alanine, aspartate, and glutamate metabolism. These findings provide a deeper understanding of taste mechanisms and establish a basis for the targeted regulation of taste formation in the fermented fish industry.

Rapid screening based on machine learning and molecular docking of umami peptides from porcine bone

BACKGROUND

The traditional screening method for umami peptide, extracted from porcine bone, was labor-intensive and time-consuming. In this study, the rapid screening method and molecular mechanism of umami peptide was investigated.

RESULTS

This article showed that a more precisely rapid screening method with composite machine learning and molecular docking was used to screen the potential umami peptide from porcine bone. As reference, 24 reported umami peptides were predicated by composite machine learning, with the accuracy of 86.7%. In this study, potential umami peptide sequences from porcine bone were screened by UMPred-FRL, Umami-MRNN Demo, and molecular docking was used to provide further screening. Finally, nine peptides were screened and verified as umami peptides by this method: LREY, HEAL, LAKVH, FQKVVA, HVKELE, AEVKKAP, EAVEKPQS, KALSEEL and KKMFETES. The hydrogen bonding was deemed to be the main interaction force with receptor T1R3, and domain binding sites were Ser146, His121 and Glu277. The result demonstrated the feasibility of machine learning assisted T1R1/T1R3 receptor for rapid screening umami peptides. The screening method would not only adapt to screen umami peptides from porcine bone but possibly applied for other sources. It also provided a reference for rapid screening of umami peptides.

CONCLUSION

The manuscript lays a rapid screening method in screening umami peptide, and nine umami peptides from porcine bone were screened and identified. © 2022 Society of Chemical Industry.

Application of electronic tongue in umami detection and soy sauce refining process

The article systematically investigated the response behaviors of lipid-film equipped umami taste sensor to various umami compounds, including typical umami substances (umami amino acids, GMP, IMP, disodium succinate) and novel umami chemicals (umami peptide and Amadori rearrangement product of umami amino acid). The umami taste sensor has great specificity to all umami substances. Relationships between output values and concentrations of umami substances in certain ranges were consistent with Weber-Fechner law. The umami synergistic effect detected by the sensor was in great agreement with human sensory results as well, fitting logarithm model. Moreover, the taste profile mixing model of raw soy sauce was established using five different taste sensors and principal component analysis, realizing the simplification of soy sauce blending and acceleration of the soy sauce refining process. Thus, flexible design of the experimental procedure and multi-analysis of the sensor data is essential.

Fractionation, identification and umami characteristics of flavor peptides in natural brewed soy sauce

To investigate the umami mechanisms and characteristics of soy sauce flavor peptides, four fractions from natural brewed soy sauce were separated using ultrafiltration and Sephadex G-15 gel filtration chromatography. Sensory and ligand-receptor interaction tests showed that the umami strengths of the fractions were related as follows: U1 > U2, G3 > G2, and G3 > U1. Peptide identification revealed that the < 550-Da peptides might be the major contributors to the umami taste of U1 and G3. The higher umami strength of G3 might be attributable to its higher content of umami peptides. G3's concentration-relative umami intensity curve was plotted using a two-alternative forced choice test. It was also revealed that less sourness, higher saltiness and cool (4 ℃) and hot (50 ℃) serving conditions were conductive to the umami perception of G3. The results could provide a reference for the application of soy-sauce flavor peptides in food.

Identification of Novel Umami Peptides in Chicken Breast Soup through a Sensory-Guided Approach and Molecular Docking to the T1R1/T1R3 Taste Receptor

Ultrafiltration combined with nanoliquid chromatography quadrupole time-of-flight mass spectrometry (nano-LC-QTOF-MS) and sensory evaluation was used to separate and identify umami peptides in chicken breast soup. Fifteen peptides with umami propensity scores of >588 were identified from the fraction (molecular weight ≤1 kDa) using nano-LC-QTOF-MS, and their concentrations ranged from 0.02 ± 0.01 to 6.94 ± 0.41 μg/L in chicken breast soup. AEEHVEAVN, PKESEKPN, VGNEFVTKG, GIQKELQF, FTERVQ, and AEINKILGN were considered as umami peptides according to sensory analysis results (detection threshold: 0.18-0.91 mmol/L). The measurement of point of subjective equality showed that these six umami peptides (2.00 g/L) were equivalent to 0.53-0.66 g/L of monosodium glutamate (MSG) in terms of umami intensity. Notably, the sensory evaluation results showed that the peptide of AEEHVEAVN significantly enhanced the umami intensity of the MSG solution and chicken soup models. The molecular docking results showed that the serine residues were the most frequently observed binding sites in T1R1/T1R3. The binding site Ser276 particularly contributed to the formation of the umami peptide-T1R1 complexes. The acidic glutamate residues observed in the umami peptides were also involved in their binding to the T1R1 and T1R3 subunits.

Effects of continuous enzymolysis on the umami characteristics of Lentinula edodes and the flavor formation mechanism of umami peptides

The purpose of this study was to explore the effect of continuous enzymolysis on the umami characteristics of Lentinula edodes and illuminate the umami mechanism of peptides. The results indicated that the continuous enzymolysis extracts (LFTE) of L.edodes had higher umami intensity and palatability than the water extracts (LWE). ¹H NMR and LC-MS/MS were used to evaluate taste metabolites and peptide profiles. Among the identified peptides, LPGVAE, LDELEK, DVELSK, LPDEAR, and TTLPDK with high umami scores which threshold in the range of 0.091-0.371 mmol/L were screened by iUmami-SCM and BIOPEP-UWM, and further verified by sensory evaluation. The results of molecular docking suggested that Ser148, Asn150, Ser276, Ser278 of T1R1 and Asn68, Val277, Ala302, Ser306 of T1R3 played a key role in the umami peptides docking. The study revealed continuous enzymolysis of L.edodes could obtain more umami substances and umami peptides, which laid a foundation for researching flavor substances and developing flavor products from L.edodes.

Six categories of amino acid derivatives with potential taste contributions: a review of studies on soy sauce

During the fermentation of soy sauce, the metabolism of microorganisms and the Maillard reaction produce a wide variety of metabolites that contribute to the unique and rich flavor characteristics of soy sauce, such as amino acids, organic acids and peptides. Amino acid derivatives, a relatively new taste compounds, formed by the reaction of enzymes or non-enzymes from sugars, amino acids, and organic acids released through metabolism by microorganisms during soy sauce fermentation, have begun to gain more and more attention in recent years. This review focused on our existing knowledge of the sources, taste characteristics and synthesis methods of the 6 categories of amino acid derivatives, including Amadori compounds, γ-glutamyl peptides, pyroglutamyl amino acids, N-lactoyl amino acids, N-acetyl amino acids and N-succinyl amino acids. Sixty-four amino acid derivatives were detected in soy sauce, of which 47 were confirmed to have potential contribution to the taste of soy sauce, especially umami and kokumi, and some of them also have the effect of reducing bitterness. Furthermore, some amino acid derivatives, like γ-glutamyl peptides and N-lactoyl amino acids, were found to be synthesized enzymatically in vitro, which laid the foundation for further study on their formation pathways in the future.

Revealing the Secret of Umami Taste of Peptides Derived from Fermented Broad Bean Paste

To understand the umami taste of fermented broad bean paste (FBBP) and explore the umami mechanism, eight peptides (PKALSAFK, NKHGSGK, SADETPR, EIKKAALDANEK, DALAHK, LDDGR, and GHENQR) were separated and identified via ultrafiltration, RP-HPLC, and UPLC-QTOF-MS/MS methods. Sensory experiments suggested that eight novel peptides showed umami/umami-enhancing and salt-enhancing functions. Significantly, the threshold of EIKKAALDANEK in aqueous solution exceeded that of most umami peptides reported in the past 5 years. The omission test further confirmed that umami peptides contributed to the umami taste of FBBP. Molecular docking results inferred that all peptides easily bind with Ser, Glu, His, and Asp residues in T1R3 through hydrogen bonds and electrostatic interactions. The aromatic interaction, hydrogen bond, hydrophilicity, and solvent-accessible surface (SAS) were the main interaction forces. This work may contribute to revealing the secret of the umami taste of FBBP and lay the groundwork for the efficient screening of umami peptides.

Identification of umami peptides based on virtual screening and molecular docking from Atlantic cod (Gadus morhua)

Umami peptides have currently become the research focus in the food umami science field and the key direction for umami agent development. This is because umami peptides have good processing characteristics, umami and nutritional values. We here used virtual screening (including online enzymolysis through ExPASy PeptideCutter, bioactivity screening using the PeptideRanker, toxicity and physicochemical property prediction using Innovagen and ToxinPred software), molecular docking, and electronic tongue analysis to identify umami peptides generated from Atlantic cod myosin. Twenty-three putative umami peptides were screened from the myosin. Molecular docking results suggested that these 23 peptides could enter the binding pocket in the T1R3 cavity, wherein Glu128 and Asp196 were the main amino acid residues, and that hydrogen bonding and electrostatic interactions were the main binding forces. Twelve synthetic peptides tested on the electronic tongue exhibited umami taste and a synergistic effect with monosodium glutamate (MSG). Among them, GGR, AGCD, and SGDAW had higher umami intensities than the other peptides, while SGDAW and NDDGW exhibited stronger umami-enhancing capabilities in 0.1% MSG solution. This study offers a method for the rapid screening of umami peptides from marine protein resources and places the foundation for their application in the food industry.

Novel Umami Peptides from Hypsizygus marmoreus and Interaction with Umami Receptor T1R1/T1R3

Umami peptides are important taste components of foods. In this study, umami peptides from Hypsizygus marmoreus hydrolysate were purified through ultrafiltration, gel filtration chromatography, and RP-HPLC, and then identified using LC-MS/MS. The binding mechanism of umami peptides with the receptor, T1R1/T1R3, was investigated using computational simulations. Five novel umami peptides were obtained: VYPFPGPL, YIHGGS, SGSLGGGSG, SGLAEGSG, and VEAGP. Molecular docking results demonstrated that all five umami peptides could enter the active pocket in T1R1; Arg277, Tyr220, and Glu301 were key binding sites; and hydrogen bonding and hydrophobic interaction were critical interaction forces. VL-8 had the highest affinity for T1R3. Molecular dynamics simulations demonstrated that VYPFPGPL (VL-8) could be steadily packed inside the binding pocket of T1R1 and the electrostatic interaction was the dominant driving force of the complex (VL-8-T1R1/T1R3) formation. Arg residues (151, 277, 307, and 365) were important contributors to binding affinities. These findings provide valuable insights for the development of umami peptides in edible mushrooms.

Bioactive and Sensory Di- and Tripeptides Generated during Dry-Curing of Pork Meat

Dry-cured pork products, such as dry-cured ham, undergo an extensive proteolysis during manufacturing process which determines the organoleptic properties of the final product. As a result of endogenous pork muscle endo- and exopeptidases, many medium- and short-chain peptides are released from muscle proteins. Many of them have been isolated, identified, and characterized, and some peptides have been reported to exert relevant bioactivity with potential benefit for human health. However, little attention has been given to di- and tripeptides, which are far less known, although they have received increasing attention in recent years due to their high potential relevance in terms of bioactivity and role in taste development. This review gathers the current knowledge about di- and tripeptides, regarding their bioactivity and sensory properties and focusing on their generation during long-term processing such as dry-cured pork meats.

The molecular mechanisms of quality difference for Alpine Qingming green tea and Guyu green tea by integrating multi-omics

Introduction

Harvest time represents one of the crucial factors concerning the quality of alpine green tea. At present, the mechanisms of the tea quality changing with harvest time have been unrevealed.

Methods

In the current study, fresh tea leaves (qmlc and gylc) and processed leaves (qmgc and gygc) picked during Qingming Festival and Guyu Festival were analyzed by means of sensory evaluation, metabolomics, transcriptomic analysis, and high-throughput sequencing, as well as their endophytic bacteria (qm16s and gy16s).

Results

The results indicated qmgc possessed higher sensory quality than gygc which reflected from higher relative contents of amino acids, and soluble sugars but lower relative contents of catechins, theaflavins, and flavonols. These differential metabolites created features of light green color, prominent freshness, sweet aftertaste, and mild bitterness for qmgc.

Discussion

Flavone and flavonol biosynthesis and phenylalanine metabolism were uncovered as the key pathways to differentiate the quality of qmgc and gygc. Endophytic bacteria in leaves further influence the quality by regulating the growth of tea trees and enhancing their disease resistance. Our findings threw some new clues on the tea leaves picking to pursue the balance when facing the conflicts of product quality and economic benefits.

Microbial succession and its effect on the formation of umami peptides during sufu fermentation

Sufu, a traditional Chinese fermented food, is famous for its unique flavor, especially umami. However, the formation mechanism of its umami peptides is still unclear. Here, we investigated the dynamic change of both umami peptides and microbial communities during sufu production. Based on peptidomic analysis, 9081 key differential peptides were identified, which mainly involved in amino acid transport and metabolism, peptidase activity and hydrolase activity. Twenty-six high-quality umami peptides with ascending trend were recognized by machine learning methods and Fuzzy c-means clustering. Then, through correlation analysis, five bacterial species (Enterococcus italicus, Leuconostoc citreum, L. mesenteroides, L. pseudomesenteroides, Tetragenococcus halophilus) and two fungi species (Cladosporium colombiae, Hannaella oryzae) were identified to be the core functional microorganisms for umami peptides formation. Functional annotation of five lactic acid bacteria indicated their important functions to be carbohydrate metabolism, amino acid metabolism and nucleotide metabolism, which proved their umami peptides production ability. Overall, our results enhanced the understanding of microbial communities and the formation mechanism of umami peptides in sufu, providing novel insights for quality control and flavor improvement of tofu products.

Toward a general and interpretable umami taste predictor using a multi-objective machine learning approach

The umami taste is one of the five basic taste modalities normally linked to the protein content in food. The implementation of fast and cost-effective tools for the prediction of the umami taste of a molecule remains extremely interesting to understand the molecular basis of this taste and to effectively rationalise the production and consumption of specific foods and ingredients. However, the only examples of umami predictors available in the literature rely on the amino acid sequence of the analysed peptides, limiting the applicability of the models. In the present study, we developed a novel ML-based algorithm, named VirtuousUmami, able to predict the umami taste of a query compound starting from its SMILES representation, thus opening up the possibility of potentially using such a model on any database through a standard and more general molecular description. Herein, we have tested our model on five databases related to foods or natural compounds. The proposed tool will pave the way toward the rationalisation of the molecular features underlying the umami taste and toward the design of specific peptide-inspired compounds with specific taste properties.

IUP-BERT: Identification of Umami Peptides Based on BERT Features

Umami is an important widely-used taste component of food seasoning. Umami peptides are specific structural peptides endowing foods with a favorable umami taste. Laboratory approaches used to identify umami peptides are time-consuming and labor-intensive, which are not feasible for rapid screening. Here, we developed a novel peptide sequence-based umami peptide predictor, namely iUP-BERT, which was based on the deep learning pretrained neural network feature extraction method. After optimization, a single deep representation learning feature encoding method (BERT: bidirectional encoder representations from transformer) in conjugation with the synthetic minority over-sampling technique (SMOTE) and support vector machine (SVM) methods was adopted for model creation to generate predicted probabilistic scores of potential umami peptides. Further extensive empirical experiments on cross-validation and an independent test showed that iUP-BERT outperformed the existing methods with improvements, highlighting its effectiveness and robustness. Finally, an open-access iUP-BERT web server was built. To our knowledge, this is the first efficient sequence-based umami predictor created based on a single deep-learning pretrained neural network feature extraction method. By predicting umami peptides, iUP-BERT can help in further research to improve the palatability of dietary supplements in the future.

Study on the relationship between structure and taste activity of the umami peptide of Stropharia rugosoannulata prepared by ultrasound

Through virtual screening, electronic tongue verification, and molecular docking technology, the structure-taste activity relationship of 47 kinds of umami peptides (octapeptide - undecapeptide) from Stropharia rugosoannulata prepared by simultaneous ultrasonic-assisted directional enzymatic hydrolysis was analyzed. The umami peptides of S.rugosoannulata can form hydrogen bond interaction and electrostatic interaction with umami receptors T1R1/T1R3. The amino acid residues at the peptides' N-terminal and C-terminal play a vital role in binding with the receptors to form a stable complex. D, E, and R are the primary amino acids in the peptides that easily bind to T1R1/T1R3. The basic amino acid in the peptides is more easily bound to T1R1, and the acidic amino acid is more easily bound to T1R3. The active amino acid sites of the receptors to which the peptides bind account for 42%-65% of the total active amino acid residues in the receptors. ASP147 and ASP219 are the critical amino acid residues for T1R1 to recognize the umami peptides, and ARG64, GLU45, and GLU48 are the critical amino acid residues for T1R3 to recognize the umami peptides. The increase in the variety and quantity of umami peptides is the main reason for improving the umami taste of the substrate prepared by synchronous ultrasound-assisted directional enzymatic hydrolysis. This study provides a theoretical basis for understanding simultaneous ultrasound-assisted directional enzymatic hydrolysis for preparing umami peptides from S.rugosoannulata, enhancing the flavor of umami, and the relationship between peptide structure and taste activity.

Fish proteins as potential precursors of taste-active compounds: an in silico study

BACKGROUND

Fish protein is a good source of amino acids and peptides with sensory properties. Theoretically, the type of protein affects the taste quality of the protein hydrolysates. To better use fish protein in the food ingredients industry, an in silico approach was adopted to evaluate the potential of fish protein to release taste-active compounds.

RESULTS

Six types of protein from seven commercial fishes were screened from the Uniprot knowledge base. The results showed that a remarkable number of umami fragments presented in myosin and parvalbumin (PB), such as glutamic acid (Glu), aspartic acid (Asp), and Asp- and Glu- containing peptides, whereas sweet amino acids and bitter peptides (e.g., Pro- and Gly- containing peptides) were mainly found in collagen (CGI) in all fish samples. After the in silico proteolysis by papain, a difference in the profile of taste-active fragments was observed among the six types of proteins. Amino acids were the main hydrolysis products of these proteins, especially umami, sweet, and bitter amino acids, significantly contributing to the taste formation of protein hydrolysates. Besides, the myosin and CGI hydrolysates were abundant in taste active peptides both in types and quantities.

CONCLUSION

Myosin is a promising protein source for producing umami fragments, and CGI seems to be a good precursor of sweet and bitter fragments. Different types of protein have an essential effect on the taste of protein hydrolysates. © 2022 Society of Chemical Industry.

Umami detection threshold among children of different ethnicities and its correlation with various indices of obesity and blood pressure

Sensitivity to savory taste has been linked to high consumption of savory foods and increased risks of obesity and hypertension. However, there are limited studies that investigate whether obesity indices are correlated with the differences in umami taste perception, particularly in children. This study aimed to investigate the umami detection threshold among children of different ethnicities and the threshold's correlation with obesity indices and blood pressure. A total of 140 subjects were recruited and consisted of a nearly equal distribution of children from three main ethnicities (37.2% Malays, 31.4% Chinese, 31.4% Indians). Umami detection threshold was measured using the two-alternative, forced-choice staircase procedure. Body weight, height, waist circumference and blood pressure of children were measured. Body composition was assessed using bioelectrical impedance analysis (BIA). Mean umami detection threshold was 1.22 ± 1.04 mM and there were no observable differences attributable to the subjects' ethnicities. Body fat percentage was negatively correlated (r = −0.171, p < 0.05), while lean body mass percentage was positively correlated (r = 0.171, p < 0.05) with umami detection threshold. These findings revealed that umami taste perception correlated with children's body composition, but not other anthropometric indicators and blood pressure. Future studies should explore the correlation between umami taste perception and children's total dietary intake.

•

The average umami detection threshold of Malaysian children was 1.22 ± 1.04 mM.

•

No gender or ethnic differences in umami detection thresholds were observed.

•

Umami taste perception was correlated only with children's body composition.

•

It is worth to consider umami taste threshold in designing low-sodium food products.

Typical Umami Ligand-Induced Binding Interaction and Conformational Change of T1R1-VFT

Umami taste receptor type 1 member 1/3 (T1R1/T1R3) heterodimer has multiple ligand-binding sites, most of which are located in T1R1-Venus flytrap domain (T1R1-VFT). However, the critical binding process of T1R1-VFT/umami ligands remains largely unknown. Herein, T1R1-VFT was prepared with a sufficient amount and functional activity, and its binding characteristics with typical umami molecules (monosodium l-glutamate, disodium succinate, beefy meaty peptide, and inosine-5'-monophosphate) were explored via multispectroscopic techniques and molecular dynamics simulation. The results showed that, driven mainly by hydrogen bond, van der Waals forces, and electrostatic interactions, T1R1-VFT bound to umami compound at 1:1 (stoichiometric interaction) and formed T1R1-VFT/ligand complex (static fluorescence quenching) with a weak binding affinity (K_a values: 252 ± 19 to 1169 ± 112 M^-1). The binding process was spontaneous and exothermic (ΔG, -17.72 to -14.26 kJ mol^-1; ΔH, -23.86 to -12.11 kJ mol^-1) and induced conformational changes of T1R1-VFT, which was mainly reflected in slight unfolding of α-helix (Δα-helix < 0) and polypeptide chain backbone structure. Meanwhile, the binding of the four ligands stabilized the active conformation of the T1R1-VFT pocket. This work provides insight into the binding interaction between T1R1-VFT/umami ligands and improves understanding of how umami receptor recognizes specific ligand molecules.

Characteristics of umami peptides identified from porcine bone soup and molecular docking to the taste receptor T1R1/T1R3

To study the umami peptides derived from porcine bone soup, ultrafiltration fractions with molecular weight less than 1 kDa were screened by sensory analysis which showed higher umami intensity. Four potential umami peptides were identified from the screened fractions by Nano-LC-Q-TOF-MS/MS, among which FSGLDGAK, FAGDDAPR and FSGLDGSK were proved to have dominant umami taste by sensory evaluation and electronic tongue. The threshold of the three peptides ranged from 0.1 mM to 0.89 mM. In addition, FSGLDGSK had the highest umami intensity and exhibited a significant umami-enhancing effect in a 0.35% monosodium glutamate solution. The results of molecular docking simulation showed that the key binding sites of taste receptor type 1 member 1 (His71, Asp108 and Glu301) and taste receptor type 1 member 3 (Glu48, Ser104 and His145) were crucial to the interaction with the umami peptides. Besides, electrostatic interaction and hydrogen bond mainly contributed to the mechanism of umami taste.

Intelligent Drug Delivery by Peptide-Based Dual-Function Micelles

To endow the polymeric prodrug with smart properties through a safe and simple method, matrix metalloproteinase (MMPs) responsive peptide GPLGVRGDG was introduced into the block copolymer to prepare TPGS₃₃₅₀-GPLGVRGDG-DOX&DOX micelles, where TPGS₃₃₅₀ is D-α-tocopheryl polyethylene glycol 3350 succinate. During the doxorubicin delivery, the cleavage of the peptide chain triggers de-PEGylation, and the remaining VRGDG sequence was retained on the surface of the micelles, which can act as a ligand to facilitate cell uptake. Moreover, the cytotoxicity of TPGS₃₃₅₀-GPLGVRGDG-DOX&DOX micelles against 4T1 cells was significantly improved, compared with TPGS₃₃₅₀-GPLGVRG-DOX&DOX micelles and TPGS₃₃₅₀-DOX&DOX micelles. During in vivo studies, TPGS₃₃₅₀-GPLGVRGDG-DOX&DOX micelles exhibited good anticancer efficacy with long circulation in the body and more efficient accumulation at the tumor site. Therefore, TPGS₃₃₅₀-GPLGVRGDG-DOX&DOX micelles have improved antitumor activity and reduced toxic side effects. This work opens new potential for exploring the strategy of drug delivery in clinical applications.

Taste GPCRs and their ligands

Taste GPCRs are expressed in taste buds on the tongue and play a key role in food choice and consumption. They are also expressed extra-orally, with various physiological roles that are currently under study. Unraveling the roles of these receptors relies on the knowledge of their ligands. Combining sensory, cell-based and computational approaches enabled the discovery of numerous agonists and several antagonists. Here we provide a short overview of taste receptor families, main recent methods for ligands discovery, and current sources of information about known ligands. The future directions that are likely to impact the taste GPCR field include focus on ligand interactions with naturally occurring polymorphisms, as well as harnessing the power of CryoEM and of multiple signaling readout techniques.

Umami polypeptide detection system targeting the human T1R1 receptor and its taste-presenting mechanism

Umami is one of five basic tastes, the elucidation of its mechanism by the study of the interaction between umami polypeptides and hT1R1 umami receptors is of great significance. However, research on umami peptides targeting human T1R1 receptors is lacking, and the molecular mechanism remains elusive. Here, we successfully established a system to detect umami peptides targeting human T1R1 receptors by fluorescence spectroscopy, Surface Plasmon Resonance (SPR) and computational simulation. The sensory evaluation, calculated Kd value, and experimental affinity results between the four selected umami peptides (GRVSNCAA, KGDEESLA, KGGGGP, and TGDPEK) and glutamate were tested using this system, and all matched well. The maximum Ka value of GRVSNCAA was 479.55 M-1, and the minimum affinity of TGDPEK was 2.67 M-1. Computational simulations showed that the different peptide binding sites in the hT1R1 binding pocket occupied due to conformational changes are important factors for different taste thresholds, and that peptide hydrophobicity plays an important role in regulating affinity. Thus, our study enables rapid screening of high-intensity umami peptides and the development of T1R1 receptor-based umami detection sensors.

Taste peptides derived from Stropharia rugosoannulata fermentation mycelium and molecular docking to the taste receptor T1R1/T1R3

This study identified the peptides in the fermentation mycelia of Stropharia rugosoannulata. The molecular weight of the peptides was below 3,000 Da. Heptapeptides to decapeptides were the main peptides in the fermentation mycelia of S. rugosoannulata. More than 50% of the peptides had salty and umami taste characteristics, and the long-chain peptides (decapeptides to 24 peptides) also played an essential role in the pleasant taste characteristics of mycelium. In the salty and umami peptide of S. rugosoannulata, the distribution of non-polar hydrophobic amino acids and polar-uncharged amino acids accounted for a relatively high proportion, and the proportion of polar-uncharged amino acids further increased, with the extension of the peptide chain. P, F, I, l, V, G, S, T, and D were the amino acids with a high proportion in the peptides. The taste peptides can bind to more than 60% of the active amino acid residues in the cavity-binding domain of the T1R1/T1R3 receptors. Hydrogen bond interaction was the primary mode of interaction between the peptides and the receptor. The first and second amino acid residues (such as S, V, E, K, G, and A) at the C-terminal and N-terminal of the peptides were easy to bind to T1R1/T1R3 receptors. Asp108, Asn150, Asp147, Glu301, Asp219, Asp243, Glu70, Asp218 in T1R1, and Glu45, Glu148, Glu301, Glu48, and Ala46 in TIR3 were the key active amino acid sites of taste peptides binding to T1R1/T1R3 receptors.

Identification of novel umami molecules via QSAR models and molecular docking

Umami substances can increase the overall taste of food and bring pleasure to people. However, it is still challenging to identify the umami molecules through virtual screening due to the crystal structure of the umami receptor being undefined. Herein, based on the hypothesis that the molecules with bitter and sweet taste characteristics may be umami molecules, this study proposed an in silico method to identify novel umami-tasting molecules in batch from SWEET-DB and BitterDB databases via the QSAR models, PCA, molecular docking and electronic tongue analysis. In total, 169 potential umami molecules were identified through QSAR modeling, PCA, and molecular docking. Of the 169 molecules, 18 were randomly selected, and all were identified as umami molecules via electronic tongue analysis. Among the 18 chosen molecules, 10 molecules could be traced back to their concentration range in food, and finally, 8 molecules were predicted to be nontoxic. This work provides a simple and efficient strategy to identify novel umami molecules, holding an excellent promise for demonstrating the crystal structure of umami receptors and taste-sensing mechanisms. Furthermore, this study opens the possibility for the practical application of new umami molecules in food.

Comprehensive Review of γ-Glutamyl Peptides (γ-GPs) and Their Effect on Inflammation Concerning Cardiovascular Health

γ-Glutamyl peptides (γ-GPs) are a group of peptides naturally found in various food sources. The unique γ-bond potentially enables them to resist gastrointestinal digestion and offers high stability in vivo with a longer half-life. In recent years, these peptides have caught researchers' attention due to their ability to impart kokumi taste and elicit various physiological functions via the allosteric activation of the calcium-sensing receptor (CaSR). This review discusses the various food sources of γ-glutamyl peptides, different synthesis modes, allosteric activation of CaSR for taste perception, and associated multiple biological functions they can exhibit, with a special emphasis on their role in modulating chronic inflammation concerning cardiovascular health.

Preparation, Sensory Characterization, and Umami-Enhancing Mechanism of Novel Peptide Glycoconjugates

Previous studies supposed that Amadori rearrangement products (ARPs) of peptides might have better umami-enhancing abilities. To confirm this, five ARPs (EP-ARP, AH-ARP, EE-ARP, β-AH-ARP, RFPHADF-ARP) were synthesized using a food-grade preparation method, and their chemical structures were clearly demonstrated by mass spectrometry and 1D/2D NMR. Sensory experiments showed that ARPs had better umami-enhancing abilities than the corresponding peptides in this research, though their enhancing performance varied. ARPs showed a synergistic effect with multiple umami substances (MSG and GMP), while their corresponding peptides did not. RFPHADF-ARP had good umami-enhancing capacity, despite that RFPHADF was a bitter peptide without any umami/umami-enhancing property. RFPHADF-ARP could bind to the T1R3, which is beneficial to the stability of the active conformation of the umami receptor. The introduction of glucose via the Maillard reaction increased the binding force of RFPHADF with the umami receptor by influencing the electron density distribution and offering more binding groups (hydroxide group).

Isolation and screening of umami peptides from preserved egg yolk by nano-HPLC-MS/MS and molecular docking

The material basis leading to the rich umami flavor of preserved egg yolk is poorly understood. This study used nano-high-performance liquid chromatography - tandem mass spectrometry (nano-HPLC-MS/MS) to isolate, identify, and screen umami peptides from preserved egg yolk. Five novel umami peptides-AGFMPLP, APYSGY, PPMF, SLSSLMK, and VAMNPVDHPH-were identified. Molecular docking showed that Phe527 on the taste receptor T1R1/T1R3 (T1R1, taste receptor type 1 member 1; T1R3, taste receptor type 1 member 3) was the key interaction site. Hydrogen bonding, electrostatic interactions, and hydrophobic interactions were the main binding forces between T1R1/T1R3 and umami peptides. These results contribute to understanding the umami peptides in preserved egg yolk and the interaction mechanism between umami peptides and umami receptors.

A survey on computational taste predictors

Taste is a sensory modality crucial for nutrition and survival, since it allows the discrimination between healthy foods and toxic substances thanks to five tastes, i.e., sweet, bitter, umami, salty, and sour, associated with distinct nutritional or physiological needs. Today, taste prediction plays a key role in several fields, e.g., medical, industrial, or pharmaceutical, but the complexity of the taste perception process, its multidisciplinary nature, and the high number of potentially relevant players and features at the basis of the taste sensation make taste prediction a very complex task. In this context, the emerging capabilities of machine learning have provided fruitful insights in this field of research, allowing to consider and integrate a very large number of variables and identifying hidden correlations underlying the perception of a particular taste. This review aims at summarizing the latest advances in taste prediction, analyzing available food-related databases and taste prediction tools developed in recent years.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00217-022-04044-5.

Characterization of Peanut Protein Hydrolysate and Structural Identification of Umami-Enhancing Peptides

Umami peptides are naturally found in various foods and have been proven to be essential components contributing to food taste. Defatted peanut powder hydrolysate produced by a multiprotease (Flavorzyme, Alcalase, and Protamex) was found to elicit an umami taste and umami-enhancing effect. The taste profiles, hydrolysis efficiency, amino acids, molecular weight distribution, Fourier transform infrared spectroscopy (FT-IR), and separation fractions obtained by ultrafiltration were evaluated. The results showed that peanut protein was extensively hydrolyzed to give mainly (up to 96.84%) free amino acids and peptides with low molecular weights (<1000 Da). Furthermore, β-sheets were the major secondary structure. Fractions of 1−3000 Da and <1000 Da prominently contributed to the umami taste and umami enhancement. To obtain umami-enhancing peptides, these two fractions were further purified by gel filtration chromatography, followed by sensory evaluation. These peptides were identified as ADSYRLP, DPLKY, EAFRVL, EFHNR, and SDLYVR by ultra-performance liquid chromatography (UPLC), and had estimated thresholds of 0.107, 0.164, 0.134, 0.148, and 0.132 mmol/L, respectively. According to the results of this work, defatted peanut powder hydrolysate had an umami taste and umami-enhancing effect, and is a potential excellent umami peptide precursor material for the food industry.