Sweet, umami and bitter taste receptors: State of the art of in silico molecular modeling approaches

Effects of umami substances as taste enhancers on salt reduction in meat products: A review

Sodium is one of the essential additives in meat processing, but excessive sodium intake may increase risk of hypertension and cardiovascular disease. However, reducing salt content while preserving its preservative effect, organoleptic properties, and technological characteristics poses challenges. In this review, the mechanism of salt reduction of umami substances was introduced from the perspective of gustation-taste interaction, and the effects of the addition of traditional umami substances (amino acids, nucleotides, organic acids(OAs)) and natural umami ingredients (mushrooms, seaweeds, tomatoes, soybeans, tea, grains) on the sensory properties of the meat with reduced-salt contents were summarized. In addition, the impacts of taste enhancers on eating quality (color, sensory, textural characteristics, and water-holding capacity (WHC)), and processing quality (lipid oxidation, pH) of meat products (MP) and their related mechanisms were also discussed. Among them, natural umami ingredients exhibit distinct advantages over traditional umami substances in terms of enhancing quality and nutritional value. On the basis of salt reduction, natural umami ingredients improve the flavor, texture, WHC and antioxidant capacity. This comprehensive review may provide the food industry with a theoretical foundation for mitigating salt consumption through the utilization of umami substances and natural ingredients.

Bitter flavors and bitter compounds in foods: identification, perception, and reduction techniques

Bitterness is one of the five basic tastes generally considered undesirable. The widespread presence of bitter compounds can negatively affect the palatability of foods. The classification and sensory evaluation of bitter compounds have been the focus in recent research. However, the rigorous identification of bitter tastes and further studies to effectively mask or remove them have not been thoroughly evaluated. The present paper focuses on identification of bitter compounds in foods, structural-based activation of bitter receptors, and strategies to reduce bitter compounds in foods. It also discusses the roles of metabolomics and virtual screening analysis in bitter taste. The identification of bitter compounds has seen greater success through metabolomics with multivariate statistical analysis compared to conventional chromatography, HPLC, LC-MS, and NMR techniques. However, to avoid false positives, sensory recognition should be combined. Bitter perception involves the structural activation of bitter taste receptors (TAS2Rs). Only 25 human TAS2Rs have been identified as responsible for recognizing numerous bitter compounds, showcasing their high structural diversity to bitter agonists. Thus, reducing bitterness can be achieved through several methods. Traditionally, the removal or degradation of bitter substances has been used for debittering, while the masking of bitterness presents a new effective approach to improving food flavor. Future research in food bitterness should focus on identifying unknown bitter compounds in food, elucidating the mechanisms of activation of different receptors, and developing debittering techniques based on the entire food matrix.

Electronic tongue, proton-transfer-reaction mass spectrometry, spectral analysis, and molecular docking characterization for determining the effect of α-amylase on flavor perception

The effects of α-amylase on of flavor perception were investigated via spectrum analysis, electronic tongue, on-line mass spectrometry, and molecular docking. Aroma release results showed that α-amylase exhibited variable release patterns of different aroma compounds. Electronic tongue analysis showed that the perception of bitterness, sweetness, sour, and saltiness was subtly increased and that of umami was significantly increased (p < 0.01) along with the increasing enzyme activity of α-amylase. Ultraviolet absorption and fluorescence spectroscopy analyses showed that static quenching occurred between α-amylase and eight flavor compounds and their interaction effects were spontaneous. One binding pocket was confirmed between the α-amylase and flavor compounds, and molecular docking simulation results showed that the hydrogen, electrostatic, and hydrophobic bonds were the main force interactions. The TYP82, TRP83, LEU173, HIS80, HIS122, ASP297, ASP206, and ARG344 were the key α-amylase amino acid residues that interacted with the eight flavor compounds.

A review on natural sweeteners, sweet taste modulators and bitter masking compounds: structure-activity strategies for the discovery of novel taste molecules

Growing demand for the tasty and healthy food has driven the development of low-calorie sweeteners, sweet taste modulators, and bitter masking compounds originated from natural sources. With the discovery of human taste receptors, increasing numbers of sweet taste modulators have been identified through human taste response and molecular docking techniques. However, the discovery of novel taste-active molecules in nature can be accelerated by using advanced spectrometry technologies based on structure-activity relationships (SARs). SARs explain why structurally similar compounds can elicit similar taste qualities. Given the characterization of structural information from reported data, strategies employing SAR techniques to find structurally similar compounds become an innovative approach to expand knowledge of sweeteners. This review aims to summarize the structural patterns of known natural non-nutritive sweeteners, sweet taste enhancers, and bitter masking compounds. Innovative SAR-based approaches to explore sweetener derivatives are also discussed. Most sweet-tasting flavonoids belong to either the flavanonols or the dihydrochalcones and known bitter masking molecules are flavanones. Based on SAR findings that structural similarities are related to the sensory properties, innovative methodologies described in this paper can be applied to screen and discover the derivatives of taste-active compounds or potential taste modulators.

Virtual screening and characteristics of novel umami peptides from porcine type I collagen

This study aimed to rapidly and precisely discover novel umami peptides from porcine type I collagen using virtual screening, sensory evaluation and molecular docking simulation. Porcine type I collagen was hydrolyzed in silico and six umami peptide candidates (CN, SM, CRD, GESMTDGF, MS, DGC) were shortlisted via umami taste, bioactivity, toxicity, allergenicity, solubility and stability predictions. The sensory evaluation confirmed that these peptides exhibited umami taste, with CRD, GESMTDGF and DGC displaying higher umami intensity and significant umami-enhancing effects in 0.35% sodium glutamate solution. Molecular docking predicted that Ser 276/384/385 of T1R1 and Asn68, Val277, Thr305, Ser306, Leu385 of T1R3 may also play critical roles in binding umami peptides. The umami taste of peptides may be perceived mainly through the formation of hydrogen bonds with the hydrophilic amino acids of T1R1/T1R3. This work provided a robust procedure and guidance to develop novel umami peptides from food byproducts.

High-pressure processing enhances saltiness perception and sensory acceptability of raw but not of cooked cured pork loins-leveraging salty and umami taste

The salt (NaCl) content in processed meats must be reduced because of its adverse effects on cardiovascular health. However, reducing salt in meat products typically leads to a lower taste intensity and, thus, consumer acceptability. Industry interventions must reduce salt content while maintaining taste, quality, and consumer acceptability. In this context, high-pressure processing (HPP) has been proposed to enhance saltiness perception, though there are contradictory reports to date. The present work aimed to conduct a targeted experiment to ascertain the influence of HPP (300/600 MPa) and cooking (71°C) on saltiness perception and sensory acceptability of meat products. HPP treatment (300/600 MPa) did enhance those two sensory attributes (approx. +1 on a 9-point hedonic scale) in raw (uncooked) cured pork loins but did not in their cooked counterparts. Further, the partition coefficient of sodium (PNa+), as an estimate of Na+ binding strength to the meat matrix, and the content of umami-taste nucleotides were investigated as potential causes. No effect of cooking (71°C) and HPP (300/600 MPa) could be observed on the PNa+ at equilibrium. However, HPP treatment at 300 MPa increased the inosine-5'-monophosphate (IMP) content in raw cured pork loins. Finally, hypothetical HPP effects on taste-mediating molecular mechanisms are outlined and discussed in light of boosting the sensory perception of raw meat products as a strategy to achieve effective salt reductions while keeping consumer acceptability.

Noteworthy Consensus Effects of D/E Residues in Umami Peptides Used for Designing the Novel Umami Peptides

Aspartic acid (D) and glutamic acid (E) play vital roles in the umami peptides. To understand their exact mechanism of action, umami peptides were collected and cut into 1/2/3/4 fragments. Connecting D/E to the N/C-termini of the fragments formed D/E consensus effect groups (DEEGs), and all fragments containing DEEG were summarized according to the ratio and ranking obtained in the above four situations. The interaction patterns between peptides in DEEG and T1R1/T1R3-VFD were compared by statistical analysis and molecular docking, and the most conservative contacts were found to be HdB_277_ARG and HdB_148_SER. The molecular docking score of the effector peptides significantly dropped compared to that of their original peptides (-1.076 ± 0.658 kcal/mol, p value < 0.05). Six types of consensus fingerprints were set according to the Top7 contacts. The exponential of relative umami was linearly correlated with ΔGbind (R2 = 0.961). Under the D/E consensus effect, the electrostatic effect of the umami peptide was improved, and the energy gap between the highest occupied molecular orbital-the least unoccupied molecular orbital (HOMO-LUMO) was decreased. The shortest path map showed that the peptides had similar T1R1-T1R3 recognition pathways. This study helps to reveal umami perception rules and provides support for the efficient screening of umami peptides based on the material richness in D/E sequences.

Characterization and sweetness-enhancing effect of peptides from yeast extract based on sensory evaluation and molecular docking approaches

Yeast extract (YE) is derived from the soluble component in yeast cells, which is rich in peptides and has been used as a sweet-enhancing agent. It has the potential to be utilized to produce natural sweet-flavored peptides or sweet-enhancing peptides. To study the synergistic effect and mechanism of sweetness-enhancing peptides derived from YE, ultrafiltration fraction with molecular weight less than 1 kDa was screened according to sensory analysis, which showed a synergistic sweetening effect in stevioside and mogroside solution. Twenty potential taste peptides were identified from the screened fractions, among which EV, AM, AVDNIPVGPN and VDNIPVGPN showed sweetness-enhancing effects on both stevioside and mogroside. The sweetener-receptor-peptide complex was constructed to investigate the interaction of stevioside and mogroside to taste receptor type 1 member 2 accompanied by these peptides. The results of the molecular docking indicated that new hydrophobic interactions (Leu 279, Pro 308, Val 309, etc.) and hydrogen bonds (Ser 40, Ala 43, Asp 278, etc.) were formed between sweeteners and active sites in the venus flytrap domain. In conclusion, the presence of sweetness-enhancing peptides from YE improved the binding stability of sweeteners and receptors by increasing the binding interaction, especially the hydrophobic interactions, which contribute to the synergistic effect of sweetness-enhancing peptides.

A screening strategy for identifying umami peptides with multiple bioactivities from Stropharia rugosoannulata using in silico approaches and SPR sensing

Umami peptides from natural resources have garnered considerable attention for their potential bioactivities and flavor-enhancing characteristics. In this study, we constructed a database comprising 123 peptides from Stropharia rugosoannulata and screened for umami peptides with both angiotensin I-converting enzyme (ACE) and dipeptidyl peptidase-4 (DPP-IV) inhibitory activities using online prediction tools and molecular docking, and further confirmed by SPR sensing, intelligent sensory and activities test. Five peptides with varying chain lengths were synthesized and by evaluations analyses they exhibited strong umami, with thresholds ranging from 0.105 mmol/L to 0.547 mmol/L. According to the targeted SPR molecular interaction analysis, umami peptides and hT1R3 receptor exhibited a "fast-on/fast-off" binding mode with stronger intensity and persistence than MSG. Furthermore, in vitro experiments revealed that five peptides showed potent ACE and DPP-IV inhibitory activities. Notably, the EAF inhibitory activity was the most significant among the peptides. This comprehensive screening strategy provides a rapid approach for identifying high-sensitivity umami peptides with bioactivities.

Molecular simulation for food protein-ligand interactions: A comprehensive review on principles, current applications, and emerging trends

In recent years, investigations on molecular interaction mechanisms between food proteins and ligands have attracted much interest. The interaction mechanisms can supply much useful information for many fields in the food industry, including nutrient delivery, food processing, auxiliary detection, and others. Molecular simulation has offered extraordinary insights into the interaction mechanisms. It can reflect binding conformation, interaction forces, binding affinity, key residues, and other information that physicochemical experiments cannot reveal in a fast and detailed manner. The simulation results have proven to be consistent with the results of physicochemical experiments. Molecular simulation holds great potential for future applications in the field of food protein-ligand interactions. This review elaborates on the principles of molecular docking and molecular dynamics simulation. Besides, their applications in food protein-ligand interactions are summarized. Furthermore, challenges, perspectives, and trends in molecular simulation of food protein-ligand interactions are proposed. Based on the results of molecular simulation, the mechanisms of interfacial behavior, enzyme-substrate binding, and structural changes during food processing can be reflected, and strategies for hazardous substance detection and food flavor adjustment can be generated. Moreover, molecular simulation can accelerate food development and reduce animal experiments. However, there are still several challenges to applying molecular simulation to food protein-ligand interaction research. The future trends will be a combination of international cooperation and data sharing, quantum mechanics/molecular mechanics, advanced computational techniques, and machine learning, which contribute to promoting food protein-ligand interaction simulation. Overall, the use of molecular simulation to study food protein-ligand interactions has a promising prospect.

Identification, Characterization, and Receptor Binding Mechanism of New Umami Peptides from Traditional Fermented Soybean Paste (Dajiang)

Dajiang, a traditional Chinese condiment, is made from fermented soybeans. It is highly popular among consumers as a result of its delicious umami flavor, which mainly originates from umami peptides. To examine the mechanism of umami taste in Dajiang, we selected Dajiang samples with strong umami taste and subjected them to purification and identification analysis using ethanol precipitation, gel chromatography, reversed-phase high-performance liquid chromatography, and ultraperformance liquid chromatography-tandem mass spectrometry. Subsequently, on the basis of toxicity and umami prediction analysis, we screened, synthesized, and characterized three novel bean umami peptides in Dajiang: TLGGPTTL, 758.4174 Da; GALEQILQ, 870.4811 Da; and HSISDLQ, 911.4713 Da. Their sensory threshold values were 0.25, 0.40, and 0.17 mmol/L, respectively. Furthermore, molecular docking results showed that hydrogen-bonding and hydrophobic interactions are important interaction forces in the binding of umami peptide to taste receptors. Ser147 and Glu148 of the T1R3 taste receptor are important amino acid residues for binding of the three umami peptides. This study uncovers the mechanism of umami-peptide-driven flavor in fermented soybean products.

Structure-Based Discovery of Mouse Trace Amine-Associated Receptor 5 Antagonists

Trace amine-associated receptors (TAARs) were discovered in 2001 as new members of class A G protein-coupled receptors (GPCRs). With the only exception of TAAR1, TAAR members (TAAR2-9, also known as noncanonical olfactory receptors) were originally described exclusively in the olfactory epithelium and believed to mediate the innate perception of volatile amines. However, most noncanonical olfactory receptors are still orphan receptors. Given its recently discovered nonolfactory expression and therapeutic potential, TAAR5 has been the focus of deorphanization campaigns that led to the discovery of a few druglike antagonists. Here, we report four novel TAAR5 antagonists identified through high-throughput screening, which, along with the four ligands published in the literature, constituted our starting point to design a computational strategy for the identification of TAAR5 ligands. We developed a structure-based virtual screening protocol that allowed us to identify three new TAAR5 antagonists with a hit rate of 10%. Despite lacking an experimental structure, we accurately modeled the TAAR5 binding site by integrating comparative sequence- and structure-based analyses of serotonin receptors with homology modeling and side-chain optimization. In summary, we have identified seven new TAAR5 antagonists that could serve as lead candidates for the development of new treatments for depression, anxiety, and neurodegenerative diseases.

Identification and Verification of Novel Umami Peptides Isolated from Hybrid Sturgeon Meat (Acipenser baerii × Acipenser schrenckii)

To explore the umami mechanism in sturgeon meat, five peptides (ERRY, VRGPR, LKYPLE, VKKVFK, and YVVFKD) were isolated and identified by ultrafiltration, gel filtration chromatography, and UPLC-QTOF-MS/MS. The omission test confirmed that the five umami peptides contributed to the umami taste of sturgeon meat. Also, the peptides had the double effective role of enhancing both umami and saltiness. The threshold of ERRY was only 0.031, which exceeded most umami peptides in the last 3 years. Molecular docking results showed that five peptides could easily bind to Gly167, Ser170, and Try218 residues in T1R3 through hydrogen bonds and electrostatic interactions. Furthermore, molecular dynamics simulations indicated that hydrogen bonds and hydrophobic interactions were the main intermolecular interaction forces. This study could contribute to revealing the umami taste mechanism of sturgeon meat and provide new insights for effective screening of short umami peptides.

Insights into brain perceptions of the different taste qualities and hedonic valence of food via scalp electroencephalogram

Investigating brain activity is essential for exploring taste-experience related cues. The paper aimed to explore implicit (unconscious) emotional or physiological responses related to taste experiences using scalp electroencephalogram (EEG). We performed implicit measures of tastants of differing perceptual types (bitter, salty, sour and sweet) and intensities (low, medium, and high). The results showed that subjects were partially sensitive to different sensory intensities, i.e., for high intensities, taste stimuli could induce activation of different rhythm signals in the brain, with α and θ bands possibly being more sensitive to different taste types. Furthermore, the neural representations and corresponding sensory qualities (e.g., "sweet: pleasant" or "bitter: unpleasant") of different tastes could be discriminated at 250-1,500 ms after stimulus onset, and different tastes exhibited distinct temporal dynamic differences. Source localization indicated that different taste types activate brain areas associated with emotional eating, reward processing, and motivated tendencies, etc. Overall, our findings reveal a larger sophisticated taste map that accounted for the diversity of taste types in the human brain and assesses the emotion, reward, and motivated behavior represented by different tastes. This study provided basic insights and a perceptual foundation for the relationship between taste experience-related decisions and the prediction of brain activity.

Sweet Taste Receptors and Associated Sweet Peptides: Insights into Structure and Function

Long-term consumption of a high-sugar diet may contribute to the pathogenesis of several chronic diseases, such as obesity and type 2 diabetes. Sweet peptides derived from a wide range of food sources can enhance sweet taste without compromising the sensory properties. Therefore, the research and application of sweet peptides are promising strategies for reducing sugar consumption. This work first outlined the necessity for global sugar reduction, followed by the introduction of sweet taste receptors and their associated transduction mechanisms. Subsequently, recent research progress in sweet peptides from different protein sources was summarized. Furthermore, the main methods for the preparation and evaluation of sweet peptides were presented. In addition, the current challenges and potential applications are also discussed. Sweet peptides can stimulate sweetness perception by binding sweet taste receptors T1R2 and T1R3 in taste buds, which is an effective strategy for reducing sugar consumption. At present, sweet peptides are mainly prepared artificially by synthesis, hydrolysis, microbial fermentation, and bioengineering strategies. Furthermore, sensory evaluation, electronic tongues, and cell models have been used to assess the sweet taste intensity. The present review can provide a theoretical reference for reducing sugar consumption with the aid of sweet peptides in the food 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.

Conserved Sites and Recognition Mechanisms of T1R1 and T2R14 Receptors Revealed by Ensemble Docking and Molecular Descriptors and Fingerprints Combined with Machine Learning

Taste peptides, as an important component of protein-rich foodstuffs, potentiate the nutrition and taste of food. Thereinto, umami- and bitter-taste peptides have been ex tensively reported, while their taste mechanisms remain unclear. Meanwhile, the identification of taste peptides is still a time-consuming and costly task. In this study, 489 peptides with umami/bitter taste from TPDB (http://tastepeptides-meta.com/) were collected and used to train the classification models based on docking analysis, molecular descriptors (MDs), and molecular fingerprints (FPs). A consensus model, taste peptide docking machine (TPDM), was generated based on five learning algorithms (linear regression, random forest, gaussian naive bayes, gradient boosting tree, and stochastic gradient descent) and four molecular representation schemes. Model interpretive analysis showed that MDs (VSA_EState, MinEstateIndex, MolLogP) and FPs (598, 322, 952) had the greatest impact on the umami/bitter prediction of peptides. Based on the consensus docking results, we obtained the key recognition modes of umami/bitter receptors (T1Rs/T2Rs): (1) residues 107S-109S, 148S-154T, 247F-249A mainly form hydrogen bonding contacts and (2) residues 153A-158L, 163L, 181Q, 218D, 247F-249A in T1R1 and 56D, 106P, 107V, 152V-156F, 173K-180F in T2R14 constituted their hydrogen bond pockets. The model is available at http://www.tastepeptides-meta.com/yyds.

Human Gingival Fibroblasts as a Novel Cell Model Describing the Association between Bitter Taste Thresholds and Interleukin-6 Release

Human gingival fibroblast cells (HGF-1 cells) present an important cell model to investigate the gingiva's response to inflammatory stimuli such as lipopolysaccharides from Porphyromonas gingivalis (Pg-LPS). Recently, we demonstrated trans-resveratrol to repress the Pg-LPS evoked release of the pro-inflammatory cytokine interleukin-6 (IL-6) via involvement of bitter taste sensing receptor TAS2R50 in HGF-1 cells. Since HGF-1 cells express most of the known 25 TAS2Rs, we hypothesized an association between a compound's bitter taste threshold and its repressing effect on the Pg-LPS evoked IL-6 release by HGF-1 cells. To verify our hypothesis, 11 compounds were selected from the chemical bitter space and subjected to the HGF-1 cell assay, spanning a concentration range between 0.1 μM and 50 mM. In the first set of experiments, the specific role of TAS2R50 was excluded by results from structurally diverse TAS2R agonists and antagonists and by means of a molecular docking approach. In the second set of experiments, the HGF-1 cell response was used to establish a linear association between a compound's effective concentration to repress the Pg-LPS evoked IL-6 release by 25% and its bitter taste threshold concentration published in the literature. The Pearson correlation coefficient revealed for this linear association was R² = 0.60 (p < 0.01), exceeding respective data for the test compounds from a well-established native cell model, the HGT-1 cells, with R² = 0.153 (p = 0.263). In conclusion, we provide a predictive model for bitter tasting compounds with a potential to act as anti-inflammatory substances.

Recent Advances in Bitterness-Sensing Systems

Bitterness is one of the basic tastes, and sensing bitterness plays a significant role in mammals recognizing toxic substances. The bitter taste of food and oral medicines may decrease consumer compliance. As a result, many efforts have been made to mask or decrease the bitterness in food and oral pharmaceutical products. The detection of bitterness is critical to evaluate how successful the taste-masking technology is, and many novel taste-sensing systems have been developed on the basis of various interaction mechanisms. In this review, we summarize the progress of bitterness response mechanisms and the development of novel sensors in detecting bitterness ranging from commercial electronic devices based on modified electrodes to micro-type sensors functionalized with taste cells, polymeric membranes, and other materials in the last two decades. The challenges and potential solutions to improve the taste sensor quality are also discussed.

Discovery of N-l-Lactoyl-l-Trp as a Bitterness Masker via Structure-Based Virtual Screening and a Sensory Approach

N-Lactoyl-amino acid derivatives (N-Lac-AAs) are of increasing interest as potential taste-active compounds. The complexity and diversity of N-Lac-AAs pose a significant challenge to the effective discovery of taste-active N-Lac-AAs. Therefore, a structure-based virtual screening was used to identify taste-active N-Lac-AAs. Virtual screening results showed that N-lactoyl-hydrophobic amino acids had a higher affinity for taste receptors, specifically N-l-Lac-l-Trp. And then, N-l-Lac-l-Trp was synthesized in yields of 22.3% by enzymatic synthesis in the presence of l-lactate and l-Trp, and its chemical structure was confirmed by MS/MS and one-dimensional (1D) and two-dimensional (2D) NMR. Sensory evaluation revealed that N-l-Lac-l-Trp had a significant taste-masking effect on quinine, d-salicin, caffeine, and l-Trp, particularly l-Trp and caffeine. N-l-Lac-l-Trp had a better masking effect on the higher concentration of bitter compounds. It reduced the bitterness of caffeine (500 mg/L) and l-Trp (1000 mg/L) by approximately 20 and 26%, respectively. The result of the ligand-receptor interaction and a quantum mechanical analysis showed that N-l-Lac-l-Trp increased the binding affinity to the bitter receptor mainly through hydrogen bonding and lowering the electrostatic potential.

Sweet Chestnut (Castanea sativa Mill.) Nutritional and Phenolic Composition Interactions with Chestnut Flavor Physiology

The European chestnut (Castanea sativa Mill.), is an environmentally and economically important species in Europe, mainly for fruit production. The chestnut fruit is well-known for its nutritional properties, namely its high concentration of carbohydrates (starch) and its low-fat content, as well as being one of the few fruits that do not contain gluten. Due to its chemical and nutritional characteristics beneficial to health, the sweet chestnut is a food recommended at different levels. The biochemistry of the mouth and nose of a human being is very complex. However, understanding the different interactions between the biochemistry of our sensory organs and food helps us to comprehend certain concepts, such as flavor and how it is involved in the sensory evaluation of the chestnuts. For the selection of high-quality products, it is necessary to develop reliable methods both from a qualitative and sensory point of view, and chestnut is a fruit with unique sensory characteristics that can be used in various gastronomic dishes, from main courses to desserts.

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.

The Taste-Masking Mechanism of Chitosan at the Molecular Level on Bitter Drugs of Alkaloids and Flavonoid Glycosides from Traditional Chinese Medicine

Taste masking of traditional Chinese medicines (TCMs) containing multiple bitter components remains an important challenge. In this study, berberine (BER) in alkaloids and phillyrin (PHI) in flavonoid glycosides, which are common bitter components in traditional Chinese medicines, were selected as model drugs. Chitosan (CS) was used to mask their unfriendly taste. Firstly, from the molecular level, we explained the taste-masking mechanism of CS on those two bitter components in detail. Based on those taste-masking mechanisms, the bitter taste of a mixture of BER and PHI was easily masked by CS in this work. The physicochemical characterization results showed the taste-masking compounds formed by CS with BER (named as BER/CS) and PHI (named as PHI/CS) were uneven in appearance. The drug binding efficiency of BER/CS and PHI/CS was 50.15 ± 2.63% and 67.10 ± 2.52%, respectively. The results of DSC, XRD, FTIR and molecular simulation further indicated that CS mainly masks the bitter taste by disturbing the binding site of bitter drugs and bitter receptors in the oral cavity via forming hydrogen bonds between its hydroxyl or amine groups and the nucleophilic groups of BER and PHI. The taste-masking evaluation results by the electronic tongue test confirmed the excellent taste-masking effects on alkaloids, flavonoid glycosides or a mixture of the two kinds of bitter components. The in vitro release as well as in vivo pharmacokinetic results suggested that the taste-masked compounds in this work could achieve rapid drug release in the gastric acid environment and did not influence the in vivo pharmacokinetic results of the drug. The taste-masking method in this work may have potential for the taste masking of traditional Chinese medicine compounds containing multiple bitter components.

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.

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.

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.

Classification Model for the Second Extracellular Loop of Class A GPCRs

The extracellular loop 2 (ECL2) is the longest and the most diverse loop among class A G protein-coupled receptors (GPCRs). It connects the transmembrane (TM) helices 4 and 5 and contains a highly conserved cysteine through which it is bridged with TM3. In this paper, experimental ECL2 structures were analyzed based on their sequences, shapes, and intramolecular contacts. To take into account the flexibility, we incorporated into our analyses information from the molecular dynamics trajectories available on the GPCRmd website. Despite the high sequence variability, shapes of the analyzed structures, defined by the backbone volume overlaps, can be clustered into seven main groups. Conformational differences within the clusters can be then identified by intramolecular interactions with other GPCR structural domains. Overall, our work provides a reorganization of the structural information of the ECL2 of class A GPCR subfamilies, highlighting differences and similarities on sequence and conformation levels.

Effect of short-term frozen storage on taste of gonads of female Eriocheir sinensis and the classification of taste quality combined with sensory evaluation and fuzzy logic model

To investigate the taste quality of gonads of Eriocheir sinensis during frozen storage, the difference in overall taste profile was determined by electronic tongue, and the contents of free amino acids and 5'-Nucleotides were measure. The results showed that the overall taste profile of samples during frozen storage could be effectively distinguished. The contents of free amino acids and 5'-Nucleotides increased with the extension of frozen storage time. The content of water-soluble substances stored at -20 ℃ was higher than those of stored at -40 and -80 ℃. In addition, taste was evaluated by equivalent umami concentrention (EUC) and taste active value (TAV). The sensory evaluation results indicated that with the extension of frozen storage time, umami, sweetness and saltiness decreased, while bitterness increased, which was inconsistent with the previous experimental results. Sensory verification experiments were carried out to prove that bitterness could inhibit umami, sweetness and saltiness. Fuzzy logic model was used to classify the taste of gonads during frozen storage, with Hypoxanthine (Hx), Lysine (Lys) and Histidine (His) as input variables and twelve flavor grades as output variables. Finally, taste was evaluated using the designed model. When the gonads were stored at -20, -40 and -80 °C, the Pearson correlation coefficients between storage time and the taste grade of gonads were 0.98, 0.99 and 0.99, respectively.

The Application of In Silico Methods on Umami Taste Receptor

The umami taste receptor is a heterodimer composed of two members of the T1R taste receptor family: T1R1 (taste receptor type 1 member 1) and T1R3 (taste receptor type 1 member 3). Taste receptor T1R1-T1R3 can be activated, or modulated, by binding to several natural ligands, such as L-glutamate, inosine-5'-monophosphate (IMP), and guanosine-5'-monophosphate (GMP). Because no structure of the umami taste receptor has been solved until now, in silico techniques, such as homology modelling, molecular docking, and molecular dynamics (MD) simulations, are used to generate a 3D structure model of this receptor and to understand its molecular mechanisms. The purpose of this chapter is to highlight how computational methods can provide a better deciphering of the mechanisms of action of umami ligands in activating the umami taste receptors leading to advancements in the taste research field.

Bitter Taste and Olfactory Receptors: Beyond Chemical Sensing in the Tongue and the Nose

Abstract

The Up-and-Coming-Scientist section of the current issue of the Journal of Membrane Biology features the invited essay by Dr. Mercedes Alfonso-Prieto, Assistant Professor at the Forschungszentrum Jülich (FZJ), Germany, and the Heinrich-Heine University Düsseldorf, Vogt Institute for Brain Research. Dr. Alfonso-Prieto completed her doctoral degree in chemistry at the Barcelona Science Park, Spain, in 2009, pursued post-doctoral research in computational molecular sciences at Temple University, USA, and then, as a Marie Curie post-doctoral fellow at the University of Barcelona, worked on computations of enzyme reactions and modeling of photoswitchable ligands targeting neuronal receptors. In 2016, she joined the Institute for Advanced Science and the Institute for Computational Biomedicine at the FZJ, where she pursues research on modeling and simulation of chemical senses. The invited essay by Dr. Alfonso-Prieto discusses state-of-the-art modeling of molecular receptors involved in chemical sensing – the senses of taste and smell. These receptors, and computational methods to study them, are the focus of Dr. Alfonso-Prieto’s research. Recently, Dr. Alfonso-Prieto and colleagues have presented a new methodology to predict ligand binding poses for GPCRs, and extensive computations that deciphered the ligand selectivity determinants of bitter taste receptors. These developments inform our current understanding of how taste occurs at the molecular level.

Graphic Abstract

Identification, taste characterization and molecular docking study of novel umami peptides from the Chinese anchovy sauce

BACKGROUND

Fish sauce has a subtle flavor with prominent umami and salty taste, and is accompanied by a certain sweetness and bitterness. In order to identify a wider range of umami peptides, Chinese southern and northern anchovy sauce were selected for the study.

RESULTS

Seventeen peptides were obtained by separation and purification, and their taste activity was predicted. Through the taste characterization and descriptive analysis, it was found that the synthesized peptides were umami and umami-enhancing peptides. Seventeen umami peptides were simulated and embedded into the umami receptor T1R1/T1R3 by inserting into the Venus flytrap domain (VFTD) of the T1R3 subunit; the interaction forces were mainly hydrogen bonding, electrostatic interaction, van der Waals force and hydrophobic interaction. According to the docking interaction energies, long-chain peptides may be easier to bind to the receptor than short-chain peptides. Asp196, Glu128 and Glu197 were the main binding sites for docking, and could affect umami synergism.

CONCLUSION

For the first time, novel umami peptides in Chinese anchovy sauce have been reported. This study is helpful for discovering umami marine resource peptides, and can provide a basis for further understanding the flavor system of anchovy sauce. © 2020 Society of Chemical Industry.

Novel umami peptides from tilapia lower jaw and molecular docking to the taste receptor T1R1/T1R3

This study aimed to isolate and identify peptides with intense umami taste from tilapia lower jaw. The aqueous extract was separated using ultrafiltration and Sephadex G-15 gel filtration chromatography. The peptide fraction with an intense umami taste was selected by sensory evaluation. The five novel peptides with strong umami taste were VADLMR, STELFK, FVGLQER, DALKKK, and VVLNPVARVE. Electronic tongue analysis and sensory evaluation showed that five peptides had obvious umami taste characteristics, and the recognition thresholds of umami peptides were in the range 0.125-0.250 mg/mL. Molecular docking was used to study the interaction of the peptides and umami taste receptor T1R1/T1R3. The five peptides could perfectly be inserted into the binding pocket of the Venus flytrap domain in the T1R3 subunit. Hydrogen bonding and hydrophobic interaction were the important interaction forces. The five peptides may bind with Asp219, Glu217, and Glu148 in T1R1/T1R3 receptor and produce the umami taste.

"Dividing and Conquering" and "Caching" in Molecular Modeling

Molecular modeling is widely utilized in subjects including but not limited to physics, chemistry, biology, materials science and engineering. Impressive progress has been made in development of theories, algorithms and software packages. To divide and conquer, and to cache intermediate results have been long standing principles in development of algorithms. Not surprisingly, most important methodological advancements in more than half century of molecular modeling are various implementations of these two fundamental principles. In the mainstream classical computational molecular science, tremendous efforts have been invested on two lines of algorithm development. The first is coarse graining, which is to represent multiple basic particles in higher resolution modeling as a single larger and softer particle in lower resolution counterpart, with resulting force fields of partial transferability at the expense of some information loss. The second is enhanced sampling, which realizes "dividing and conquering" and/or "caching" in configurational space with focus either on reaction coordinates and collective variables as in metadynamics and related algorithms, or on the transition matrix and state discretization as in Markov state models. For this line of algorithms, spatial resolution is maintained but results are not transferable. Deep learning has been utilized to realize more efficient and accurate ways of "dividing and conquering" and "caching" along these two lines of algorithmic research. We proposed and demonstrated the local free energy landscape approach, a new framework for classical computational molecular science. This framework is based on a third class of algorithm that facilitates molecular modeling through partially transferable in resolution "caching" of distributions for local clusters of molecular degrees of freedom. Differences, connections and potential interactions among these three algorithmic directions are discussed, with the hope to stimulate development of more elegant, efficient and reliable formulations and algorithms for "dividing and conquering" and "caching" in complex molecular systems.

Bitter taste in silico: A review on virtual ligand screening and characterization methods for TAS2R-bitterant interactions

The growing pharmaceutical interest in the human bitter taste receptors (hTAS2Rs) has two dimensions; i) evaluation of the bitterness of active pharmaceutical compounds, in order to develop strategies for improving patients' adherence to medication, and ii) application of ligands for extra-cellular hTAS2Rs for potential preventive therapeutic achievements. The result is an increasing demand on robust tools for bitterness assessment and screening the receptor-ligand affinity. In silico tools are useful for aiding experimental-screening, as well as to elucide ligand-receptor interactions. In this review, the ligand-based and structure-based approaches are described as the two main in silico tools for bitter taste analysis. The strengths and weaknesses of each approach are discussed. Both approaches provide key tools for understanding and exploiting bitter taste for human health applications.

In-silico screening of database for finding potential sweet molecules: A combined data and structure based modeling approach

In this study, we present a framework comprises of several independent modules which are built upon data based (structure activity relationship and classification model) and structure (molecular docking) based for identifying possible sweeteners from a vast database of natural molecules. A large database, Universal Natural Products Database (UNPD) consisting of 213,210 compounds was screened using the developed framework. At first, 10,184 molecules structurally similar to the known sweeteners were identified in the database. Further, 1924 molecules from these screened molecules were classified as sweet molecules. The shortlisted 1354 molecules were subjected to ADMET analysis. Finally, 60 molecules were arrived at with no toxicity and acceptable oral bioavailability as potential sweetener candidates. Further, molecular docking of these molecules on sweet taste receptor performed to obtain their binding energy, binding sites and correlation with sweetness index. The developed framework offers a convenient route for fast screening of molecules prior to synthesis and testing.

In Silico Molecular Study of Tryptophan Bitterness

Tryptophan is an essential amino acid, required for the production of serotonin. It is the most bitter amino acid and its bitterness was found to be mediated by the bitter taste receptor TAS2R4. Di-tryptophan has a different selectivity profile and was found to activate three bitter taste receptors, whereas tri-tryptophan activated five TAS2Rs. In this work, the selectivity/promiscuity profiles of the mono-to-tri-tryptophans were explored using molecular modeling simulations to provide new insights into the molecular recognition of the bitter tryptophan. Tryptophan epitopes were found in all five peptide-sensitive TAS2Rs and the best tryptophan epitope was identified and characterized at the core of the orthosteric binding site of TAS2R4.

Sugar Reduction in Dairy Food: An Overview with Flavoured Milk as an Example

Owing to the public health concern associated with the consumption of added sugar, the World Health Organization recommends cutting down sugar in processed foods. Furthermore, due to the growing concern of increased calorie intake from added sugar in sweetened dairy foods, the present review provides an overview of different types and functions of sugar, various sugar reduction strategies, and current trends in the use of sweeteners for sugar reduction in dairy food, taking flavoured milk as a central theme where possible to explore the aforementioned aspects. The strength and uniqueness of this review are that it brings together all the information on the available types of sugar and sugar reduction strategies and explores the current trends that could be applied for reducing sugar in dairy foods without much impact on consumer acceptance. Among different strategies for sugar reduction, the use of natural non-nutritive sweeteners (NNSs), has received much attention due to consumer demand for natural ingredients. Sweetness imparted by sugar can be replaced by natural NNSs, however, sugar provides more than just sweetness to flavoured milk. Sugar reduction involves multiple technical challenges to maintain the sensory properties of the product, as well as to maintain consumer acceptance. Because no single sugar has a sensory profile that matches sucrose, the use of two or more natural NNSs could be an option for food industries to reduce sugar using a holistic approach rather than a single sugar reduction strategy. Therefore, achieving even a small sugar reduction can significantly improve the diet and health of an individual.

Structure-dependent effects of sweet and sweet taste affecting compounds on their sensorial properties

A reduction in sugar consumption is desirable from a health point of view. However, the sensory profiles of alternative sweet tasting compounds differ from sucrose regarding their temporal profile and undesired side tastes, reducing consumers' acceptance. The present study describes a sensory characterization of a variety of sweet and sweet taste affecting compounds followed by a comparison of similarity to sucrose and a multivariate regression analysis to investigate structural determinants and possible interactions for the temporal profile of the sweetness and side-tastes. The results of the present study suggest a pivotal role for the number of ketones, aromatic rings, double bonds and the M LogP in the temporal profile of sweet and sweet taste affecting compounds. Furthermore, interactions between aggregated physicochemical descriptors demonstrate the complexity of the sensory response, which should be considered in future models to predict a comprehensive sensory profile of sweet and sweet taste affecting compounds.

In Silico Investigation of Bitter Hop-Derived Compounds and Their Cognate Bitter Taste Receptors

The typical bitter taste of beer is caused by adding hops (Humulus lupulus L.) during the wort boiling process. The bitter taste of hop-derived compounds was found to be mediated by three bitter taste receptors: TAS2R1, TAS2R14, and TAS2R40. In this work, structural bioinformatics analyses were used to characterize the binding modes of trans-isocohumulone, trans-isohumulone, trans-isoadhumulone, cis-isocohumulone, cis-isohumulone, cis-isoadhumulone, cohumulone, humulone, adhumulone, and 8-prenylnaringenin into the orthosteric binding site of their cognate receptors. A conserved asparagine in transmembrane 3 was found to be essential for the recognition of hop-derived compounds, whereas the surrounding residues in the binding site of the three receptors encode the ligand specificity. Hop-derived compounds are renowned bioactive molecules and are considered as potential hit molecules for drug discovery to treat metabolic diseases. A chemoinformatics analysis revealed that hop-derived compounds cluster in a different region of the chemical space compared to known bitter food-derived compounds, pinpointing hop-derived compounds as a very peculiar class of bitter compounds.