New Umami Amides: Structure-Taste Relationship Studies of Cinnamic Acid Derived Amides and the Natural Occurrence of an Intense Umami Amide in Zanthoxylum piperitum

Investigation of bioactive components responsible for the antibacterial and anti-biofilm activities of Caroxylon volkensii by LC-QTOF-MS/MS analysis and molecular docking

Caroxylon volkensii is a wild desert plant of the family Amaranthaceae. This study represents the first report of the metabolomic profiling of C. volkensii by liquid chromatography quadrupole-time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS). The dereplication study of its secondary metabolites led to the characterization of 66 known compounds. These compounds include catecholamines, tyramine derivatives, phenolic acids, triterpenoids, flavonoids, and others. A new tyramine derivative, alongside other known compounds, was reported for the first time in the Amaranthaceae family. The new derivative and the first-reported compounds were putatively identified through MS/MS fragmentation data. Given the notorious taxonomical challenges within the genus Salsola, to which C. volkensii previously belonged, our study could offer a valuable insight into its chemical fingerprint and phylogenetic relationship to different Salsola species. The antibacterial potential of C. volkensii methanolic extract (CVM) against Pseudomonas aeruginosa was screened. The minimum inhibitory concentration (MIC) of CVM ranged from 32 to 256 μg mL-1. The anti-quorum sensing potential of CVM resulted in a decrease in the percentage of strong and moderate biofilm-forming isolates from 47.83% to 17.39%. It revealed a concentration-dependent inhibitory activity on violacein formation by Chromobacterium violaceum. Moreover, CVM exhibited an in vivo protective potential against the killing capacity of P. aeruginosa isolates. A molecular docking study revealed that the quorum-sensing inhibitory effect of CVM can be attributed to the binding of tyramine conjugates, ethyl-p-digallate, and isorhamnetin to the transcriptional global activator LasR.

SERS determination of hydroxy-α-sanshool in spicy hotpot seasoning: The strategy to restrain the interference of capsaicin and its mechanism

Hydroxy-α-sanshool (α-SOH) is the principal ingredient responsible for the numbing sensation in spicy hotpot. However, utilizing surface-enhanced Raman scattering (SERS) to analyze the α-SOH in hotpot seasoning is challenging due to the significant interference of capsaicin (CAP). Therefore, two schemes were proposed to address CAP interference in hotpot seasoning, namely laccase-catalyzed conversion and metal-organic framework (MOF) interaction. Among them, Fe-BTC MOF exhibited significant anti-interference effect and the underlying mechanism is elucidated. The motion of CAP aromatic ring was constrained by steric hindrance and electrostatic interactions of Fe-BTC. Additionally, the interaction between CAP aromatic ring and conjugated triene group in α-SOH was quenched, enhancing the α-SOH SERS signal. The proposed method had a significant anti-interference effect on α-SOH quantification in the presence of CAP, significantly enhancing the α-SOH SERS signal in a range of 0.85 to 4.00 × 10⁷. The linearity and reproducibility of the proposed hotpot seasoning testing method were also validated.

Reaction Mixtures Rich in [γ-Glu](n≥1)-Arg Derived from Enzymatic Synthesis as Potential Salt and Umami Enhancers

Some arginyl dipeptides and γ-glutamyl peptides have been identified as salt and umami enhancers. These compounds provide an operable approach for reducing sodium uptake without losing the palatability of foods. γ-Glu-Arg was hinted to have a taste-enhancing effect in the past, but few research studies have focused on it. In the present study, a series of γ-glutamyl peptides containing Arg such as γ-Glu-Arg, [γ-Glu]_(n=2)-Arg, [γ-Glu]_(n=3)-Arg, [γ-Glu]_(n=4)-Arg, [γ-Glu]_(n=5)-Arg, [γ-Glu]_(n=6)-Arg, [γ-Glu]_(n=7)-Arg, and [γ-Glu]_(n=8)-Arg were synthesized using glutaminase from Bacillus amyloliquefaciens in the presence of Gln and Arg. A high solid concentration of 30% was found to increase the production of [γ-Glu]_(1≤n≤4)-Arg. Sensory evaluation revealed that individual [γ-Glu]_(n=1,2,3,4)-Arg has a slightly bitter and astringent taste. [γ-Glu]_(n=1,2)-Arg (1.0 mg/mL) significantly increased the umaminess in the mixture of salt and sodium glutamate but showed no significant effect on saltiness in the salt solution, whereas [γ-Glu]_(n=3,4)-Arg and postenzymatic reaction mixtures (1.0 mg/mL) significantly increased both saltiness and umaminess. [γ-Glu]_(n=3,4)-Arg and postenzymatic mixtures in the system with 30% solid concentrations showed a high and similar taste-enhancing effect. Moreover, umaminess and saltiness increased 1.9 and 2.4 times in the simulated broth, respectively, while saltiness increased 1.5 times in the salt solution by the addition of postenzymatic reaction mixtures in the system with 30% solid concentrations at 20.0 mg/mL. These results indicated that [γ-Glu]_(n=1,2,3,4)-Arg and postenzymatic reaction mixtures rich in [γ-Glu]_(n≥1)-Arg were potential salt or umami enhancers.

Pharmacology of the Umami Taste Receptor

Umami, the fifth taste, has been recognized as a legitimate taste modality only recently relative to the other tastes. Dozens of compounds from vastly different chemical classes elicit a savory (also called umami) taste. The prototypical umami substance glutamic acid or its salt monosodium glutamate (MSG) is present in numerous savory food sources or ingredients such as kombu (edible kelp), beans, soy sauce, tomatoes, cheeses, mushrooms, and certain meats and fish. Derivatives of glutamate (Glu), other amino acids, nucleotides, and small peptides can also elicit or modulate umami taste. In addition, many potent umami tasting compounds structurally unrelated to amino acids, nucleotides, and MSG have been either synthesized or discovered as naturally occurring in plants and other substances. Over the last 20 years several receptors have been suggested to mediate umami taste, including members of the metabotropic and ionotropic Glu receptor families, and more recently, the heterodimeric G protein-coupled receptor, T1R1/T1R3. Careful assessment of representative umami tasting molecules from several different chemical classes shows activation of T1R1/T1R3 with the expected rank order of potency in cell-based assays. Moreover, 5'-ribonucleotides, molecules known to enhance the savory note of Glu, considerably enhance the effect of MSG on T1R1/T1R3 in vitro. Binding sites are found on at least 4 distinct locations on T1R1/T1R3, explaining the propensity of the receptor to being activated or modulated by many structurally distinct compounds and these binding sites allosterically interact to modulate receptor activity. Activation of T1R1/T1R3 by all known umami substances evaluated and the receptor's pharmacological properties are sufficient to explain the basic human sensory experience of savory taste and it is therefore unlikely that other receptors are involved.

Discovery of Novel Isothiazole, 1,2,3-Thiadiazole, and Thiazole-Based Cinnamamides as Fungicidal Candidates

A series of isothiazole, 1,2,3-thiadiazole, and thiazole-based cinnamamide morpholine derivatives were rationally designed, synthesized, characterized, and evaluated for their fungicidal activities. Bioassay indicated that a combination of 3,4-dichloroisothiazole active substructures with cinnamamide morpholine lead to significant improvement of in vivo antifungal activities of the target compounds; among them, compound 5a exhibited good fungicidal activity against Pseudoperonspera cubensis in vivo with an inhibition rate of 100% at 100 μg/mL. A field experiment indicated that the difference of efficacy between 5a (75.9%) and dimethomorph (77.1%) at 37.5 g ai/667 m² was not significant; and 5a also exhibited good activity against Botrytis cinerea by triggering accumulation of PAL and NPR1 defense-related gene expression and the defense associated enzyme phenylalanine ammonia-lyase (PAL) expression on cucumber, rather than direct inhibition. These findings strongly supported that 3,4-dichloroisothiazole containing cinnamamide morpholine 5a not only showed good fungicidal activity against P. cubensis but also exhibited plant innate immunity stimulation activity as a promising fungicide candidate with both fungicidal activity and systemic acquired resistance.

Taste Modulating Peptides from Overfermented Cocoa Beans

Activity-guided fractionation of an aqueous extract of overfermented cocoa beans, which were recently found to be a rich source of previously unknown taste enhancing substances, revealed the presence of a series of taste modulating short peptides. Fractionation was achieved by means of sequential solvent extraction, medium pressure liquid chromatography, as well as preparative high pressure liquid chromatography, and the taste modulating activity was determined by means of matrix assisted taste dilution analysis. By means of ultra performance liquid chromatography-time-of-flight-mass spectrometry (UPLC-ToF-MS) screening, liquid chromatography-MS/MS methods, and customized syntheses, numerous short peptides could be identified in the taste modulating fractions. Sensory experiments of the target peptides showed umami enhancing and salt taste enhancing properties as well as kokumi effects when applied in a savory taste matrix. Evaluation of the taste threshold concentrations in model broth demonstrated a high taste modulating potential of 11 out of 13 identified peptides. Lowest threshold concentrations were determined for the salt taste enhancing tripeptide pEEE (55 μmol/L) and the kokumi active tripeptide VPA (90 μmol/L). Furthermore, a large number of dipeptides, carrying either a prolyl- or pyro-glutamyl moiety were located in the aqueous extract, exhibiting taste modulating properties and revealing a pH dependency of the taste modulating effect of the savory taste matrix. Additionally, synergistic effects of a mixture of five umami enhancing pyro-glutamyl dipeptides in the model matrix were demonstrated.

Design, synthesis, and taste evaluation of a high-intensity umami-imparting oxazole-based compound

Umami taste is imparted predominantly by monosodium glutamate (MSG) and 5′-ribonucleotides. Recently, several different classes of hydrophobic umami-imparting compounds, the structures of which are quite different from MSG, have been reported. To obtain a novel umami-imparting compound, N-cinnamoyl phenethylamine was chosen as the lead compound, and a rational structure-optimization study was conducted on the basis of the pharmacophore model of previously reported compounds. The extremely potent umami-imparting compound 2-[[[2-[(1E)-2-(1,3-benzodioxol-5-yl)ethenyl]-4-oxazolyle]methoxy]methyl]pyridine, which exhibits 27,000 times the umami taste of MSG, was found. Its terminal pyridine residue and linear structure are suggested to be responsible for its strong activity. The time taken to reach maximum taste intensity exhibited by it, as determined by the time-intensity method, is 22.0 s, whereas the maximum taste intensity of MSG occurs immediately. This distinct difference in the time-course taste profile may be due to the hydrophobicity and strong receptor affinity of the new compound.

Rubemamine and Rubescenamine, Two Naturally Occurring N-Cinnamoyl Phenethylamines with Umami-Taste-Modulating Properties

Sensory screening of a series of naturally occurring N-cinnamoyl derivatives of substituted phenethylamines revealed that rubemamine (9, from Chenopodium album) and rubescenamine (10, from Zanthoxylum rubsecens) elicit strong intrinsic umami taste in water at 50 and 10 ppm, respectively. Sensory tests in glutamate- and nucleotide-containing bases showed that the compounds influence the whole flavor profile of savory formulations. Both rubemamine (9) and rubescenamine (10) at 10-100 ppm dose-dependently positively modulated the umami taste of MSG (0.17-0.22%) up to threefold. Among the investigated amides, only rubemamine (9) and rubescenamine (10) are able to directly activate the TAS1R1-TAS1R3 umami taste receptor. Moreover, both compounds also synergistically modulated the activation of TAS1R1-TAS1R3 by MSG. Most remarkably, rubemamine (9) was able to further positively modulate the IMP-enhanced TAS1R1-TAS1R3 response to MSG ∼ 1.8-fold. Finally, armatamide (11), zanthosinamide (13), and dioxamine (14), which lack intrinsic umami taste in vivo and direct receptor response in vitro, also positively modulated receptor activation by MSG about twofold and the IMP-enhanced MSG-induced TAS1R1-TAS1R3 responses approximately by 50%. In sensory experiments, dioxamine (14) at 25 ppm in combination with 0.17% MSG exhibited a sensory equivalent to 0.37% MSG.