(+)-(S)-alapyridaine--a general taste enhancer?

N-(1-Carboxyethyl)-6-hydroxymethyl-pyridinium-3-ol inner salt (alapyridaine), recently identified in heated sugar/amino acid mixtures as well as in beef bouillon, has been shown to exhibit general taste-enhancing activities, although tasteless on its own. Differing from other taste enhancers reported so far, racemic (R/S)-alapyridaine and, to an even greater extent (+)-(S)-alapyridaine, the physiologically active enantiomer, are able to enhance more than one basic taste quality. The threshold concentrations for the sweet taste of glucose and sucrose, for the umami taste of monosodium L-glutamate (MSG) and guanosine-5'-monophosphate (GMP), as well as the salty taste of NaCl, were significantly decreased when alapyridaine was present. In contrast, perception of the bitter tastes of caffeine and L-phenylalanine, as well as of sour-tasting citric acid, was unaffected. Furthermore, alapyridaine was shown to intensify known taste synergies such as, for example, the enhancing effect of L-arginine on the salty taste of NaCl, as well as that of GMP on the umami taste of MSG. The activity of (+)-(S)-alapyridaine could be observed not only in solutions of single taste compounds, but also in more complex tastant mixtures; for example, the umami, sweet and salty taste of a solution containing MSG, sucrose, NaCl and caffeine was significantly modulated, thus indicating that alapyridaine is a general taste enhancer.     

Monosodium glutamate and sweet taste: generalization of conditioned taste aversion between glutamate and sweet stimuli in rats

Even though monosodium glutamate (MSG) is a prototypical umami substance, previous studies reported that a conditioned taste aversion (CTA) to MSG, mixed with amiloride to block the taste of sodium, generalizes to sucrose. These findings suggest that the taste of glutamate mimics the taste of sucrose and raise the question of whether glutamate has a broadly tuned sweet taste component. To test this hypothesis, CTA experiments were conducted to test for generalization between MSG and several sweet stimuli: sucrose, glucose, maltose, saccharin and SC-45647. Strong bidirectional generalization was seen between MSG mixed with amiloride and sucrose, glucose, saccharin and SC-45647. Weak generalization was seen between MSG and maltose, and sucrose and maltose. None of the CTAs generalized to NMDA. These findings support the hypothesis that the taste of MSG has broadly tuned, sweet-like characteristics, possibly due to the convergence of afferent signals for MSG, natural sugars and artificial sweeteners.     

An analysis of 5'-inosine and 5'-guanosine monophosphate taste in rats

Inosine monophosphate (IMP) and guanosine monophosphate (GMP) elicit an umami taste in humans and synergistically increase the intensity of the umami taste of monosodium glutamate (MSG). Conditioned taste aversion (CTA) studies in rodents indicate that these nucleotides and MSG elicit quite similar tastes, but recent physiological evidence suggests that these nucleotides and MSG may not activate the same population of taste receptors and therefore may not elicit identical taste qualities. This study reports the findings of several behavioral experiments with rats that compared the taste properties of IMP and GMP with each other and with those of MSG. Well-trained rats were able to detect both nucleotides at nanomolar concentrations, but they did not respond to either nucleotide in two-bottle preference tests or brief-access CTA tests at concentrations less than 0.5 mM. Discrimination experiments found that the tastes of these nucleotides could not be discriminated from each other, but both could be discriminated from MSG, even when the taste of Na(+) was controlled. Overall, these experiments indicate the taste properties of the two 5'-ribonucleotides are quite similar to each other, and even though they may elicit an umami sensation, these sensations are not identical to the taste of MSG.     

Gustatory neural responses to umami taste stimuli in C57BL/6ByJ and 129P3/J mice

In long-term two-bottle tests, mice from the C57BL/6ByJ (B6) strain drink more monosodium L-glutamate (MSG) and inosine-5'-monophosphate (IMP) compared with mice from the 129P3/J (129) strain. The goal of this study was to assess the role of afferent gustatory input in these strain differences. We measured integrated responses of the mouse chorda tympani and glossopharyngeal nerves to lingual application of compounds that evoke umami taste in humans: MSG, monoammonium L-glutamate (NH(4) glutamate), IMP and guanosine-5'-monophosphate (GMP) and also to other taste stimuli. Chorda tympani responses to MSG and NH(4) glutamate were similar in B6 and 129 mice. Chorda tympani responses to IMP and GMP were lower in B6 than in 129 mice. Responses to umami stimuli in the glossopharyngeal nerve did not differ between the B6 and 129 strains. Responses to MSG, IMP and GMP were not affected by sodium present in these compounds because B6 and 129 mice had similar neural taste responses to NaCl. This study has demonstrated that the increased ingestive responses to the umami stimuli in B6 mice are accompanied by either unchanged or decreased neural responses to these stimuli. Lack of support for the role of the chorda tympani or glossopharyngeal nerves in the enhanced consumption of MSG and IMP by B6 mice suggests that it is due to some other factors. Although results of our previous study suggest that postingestive effects of MSG can affect its intake, contribution of other gustatory components (e.g. greater superficial petrosal nerve or central gustatory processing) to the strain differences in consumption of umami compounds also cannot be excluded. Strain differences in gustatory neural responses to nucleotides but not glutamate suggest that these compounds may activate distinct taste transduction mechanisms.     

Synergistic responses of the chorda tympani to mixtures of umami and sweet substances in rats

It has been known that umami substances such as monosodium L-glutamate (MSG) and 5'-inosine monophosphate (IMP) elicit a unique taste called 'umami' in humans. One of the characteristics of the umami taste is synergism: the synergistic enhancement of the magnitude of response produced by the addition of 5'-ribonucleotides to MSG. In addition to this well-documented synergism, we report here for the first time on another type of synergism between a glutamate receptor agonist, L-AP4, and sweet substances, by analyzing the chorda tympani responses in rats. The results are as follows: (i) when L-AP4 was mixed with one of the sweet substances, such as sucrose, glucose, fructose and maltose, large synergistic responses were observed. (ii) These synergistic responses, except to L-AP4 + sucrose, were not suppressed by sweet taste suppressants, gurmarin and pronase E. (iii) These synergistic responses were not suppressed by either metabotropic or ionotropic glutamate receptor antagonists. (iv) Fibers that responded well to the binary mixtures of L-AP4 and sweet substances also responded well to NaCl and HCl, but very weakly to sucrose. These findings are different from the characteristics of synergism between glutamate and IMP. The multiple transduction mechanisms for the umami taste in rat taste cells are discussed.     

Umami changes intracellular Ca2+ levels using intracellular and extracellular sources in mouse taste receptor cells

Recently, candidates for umami receptors have been identified in taste cells, but the precise transduction mechanisms of the downstream receptor remain unknown. To investigate how intracellular Ca(2+) increases in the umami transduction pathway, we measured changes in intracellular Ca(2+) levels in response to umami stimuli monosodium glutamate (MSG), IMP, and MSG + IMP in mouse taste receptor cells (TRCs) by Ca(2+) imaging. Even when extracellular Ca(2+) was absent, 1/3 of umami-responsive TRCs exhibited increased intracellular Ca(2+) levels. When intracellular Ca(2+) was depleted, half of the TRCs retained their response to umami. These results suggest that umami-responsive TRCs increase their intracellular Ca(2+) levels through two pathways: by releasing Ca(2+) from intracellular stores and by an influx of Ca(2+) from extracellular sources. We conclude that the Ca(2+) influx from extracellular source might play an important role in the synergistic effect between MSG and IMP.     

Genetic and Molecular Basis of Individual Differences in Human Umami Taste Perception

Umami taste (corresponds to savory in English) is elicited by L-glutamate, typically as its Na salt (monosodium glutamate: MSG), and is one of five basic taste qualities that plays a key role in intake of amino acids. A particular property of umami is the synergistic potentiation of glutamate by purine nucleotide monophosphates (IMP, GMP). A heterodimer of a G protein coupled receptor, TAS1R1 and TAS1R3, is proposed to function as its receptor. However, little is known about genetic variation of TAS1R1 and TAS1R3 and its potential links with individual differences in umami sensitivity. Here we investigated the association between recognition thresholds for umami substances and genetic variations in human TAS1R1 and TAS1R3, and the functions of TAS1R1/TAS1R3 variants using a heterologous expression system. Our study demonstrated that the TAS1R1-372T creates a more sensitive umami receptor than -372A, while TAS1R3-757C creates a less sensitive one than -757R for MSG and MSG plus IMP, and showed a strong correlation between the recognition thresholds and in vitro dose - response relationships. These results in human studies support the propositions that a TAS1R1/TAS1R3 heterodimer acts as an umami receptor, and that genetic variation in this heterodimer directly affects umami taste sensitivity.     

Obese Women Have Lower Monosodium Glutamate Taste Sensitivity and Prefer Higher Concentrations Than Do Normal‐weight Women

The goal of this study was to determine whether obese women exhibit altered umami and sweet taste perception compared to normal‐weight women. A total of 57 subjects (23 obese and 34 normal weight) participated in a 2‐day study separated by 1 week. Half of the women in each group were evaluated using monosodium glutamate (MSG; prototypical umami stimulus) on the first test day and sucrose on the second test day; the order was reversed for the remaining women. We used two‐alternative forced‐choice staircase procedures to measure taste detection thresholds, forced‐choice tracking technique to measure preferences, the general Labeled Magnitude Scale (gLMS) to measure perceived intensity of suprathreshold concentrations, and a triangle test to measure discrimination between 29 mmol/l MSG and 29 mmol/l NaCl. Obese women required higher MSG concentrations to detect a taste and preferred significantly higher MSG concentrations in a soup‐like vehicle. However, their perception of MSG at suprathreshold concentrations, their ability to discriminate MSG from salt, and their preference for sucrose were similar to that observed in normal‐weight women. Regardless of their body weight category, 28% of the women did not discriminate 29 mmol/l MSG from 29 mmol/l NaCl (nondiscriminators). Surprisingly, we found that, relative to discriminators, nondiscriminators perceived less savoriness when tasting suprathreshold MSG concentrations and less sweetness from suprathreshold sucrose concentrations but had similar MSG and sucrose detection thresholds. Taken together, these data suggest that body weight is related to some components of umami taste and that different mechanisms are involved in the perception of threshold and suprathreshold MSG concentrations.     

Behavioral evidence for a role of alpha-gustducin in glutamate taste

The taste perception of monosodium glutamate (MSG) is termed 'umami'. Two putative taste receptors for glutamate have been identified, a truncated form of mGluR4 (taste-mGluR4) and the presumed heterodimer T1R1 + T1R3. Both receptors respond to glutamate when expressed in heterologous cells, but the G protein involved is not known. Galpha-Gustducin mediates the transduction of several bitter and sweet compounds; however, its role in umami has not been determined. We used standard two-bottle preference tests on alpha-gustducin knockout (KO) and wildtype (WT) mice to compare preferences for ascending concentrations of MSG and MSG + 5'-inosine monophosphate (IMP). A Latin Square was used to assign the order of tastants presented to each mouse. Statistical comparisons between KO and WT mice revealed that whereas WT mice preferred solutions of MSG and MSG + IMP over water, KO mice showed little preference for these stimuli. Denatonium and sucrose served as control stimuli and, as shown previously, WT mice prefered sucrose and avoided denatonium significantly more than did KO mice. Na?ve mice were also tested, and while prior exposure to taste stimuli influenced the magnitude of the preferences, experience did not change the overall pattern of intake. These data suggest that alpha-gustducin plays a role in glutamate taste.     

Modulation of Sweet Taste by Umami Compounds via Sweet Taste Receptor Subunit hT1R2

Although the five basic taste qualities—sweet, sour, bitter, salty and umami—can be recognized by the respective gustatory system, interactions between these taste qualities are often experienced when food is consumed. Specifically, the umami taste has been investigated in terms of whether it enhances or reduces the other taste modalities. These studies, however, are based on individual perception and not on a molecular level. In this study we investigated umami-sweet taste interactions using umami compounds including monosodium glutamate (MSG), 5’-mononucleotides and glutamyl-dipeptides, glutamate-glutamate (Glu-Glu) and glutamate-aspartic acid (Glu-Asp), in human sweet taste receptor hT1R2/hT1R3-expressing cells. The sensitivity of sucrose to hT1R2/hT1R3 was significantly attenuated by MSG and umami active peptides but not by umami active nucleotides. Inhibition of sweet receptor activation by MSG and glutamyl peptides is obvious when sweet receptors are activated by sweeteners that target the extracellular domain (ECD) of T1R2, such as sucrose and acesulfame K, but not by cyclamate, which interact with the T1R3 transmembrane domain (TMD). Application of umami compounds with lactisole, inhibitory drugs that target T1R3, exerted a more severe inhibitory effect. The inhibition was also observed with F778A sweet receptor mutant, which have the defect in function of T1R3 TMD. These results suggest that umami peptides affect sweet taste receptors and this interaction prevents sweet receptor agonists from binding to the T1R2 ECD in an allosteric manner, not to the T1R3. This is the first report to define the interaction between umami and sweet taste receptors.     

Nerve and behavioral responses of mice to various umami substances

Food contains various taste substances. Among them, umami substances play an important role with regard to the perception of the taste of food, but, few studies have examined the taste characteristics of representative umami substances other than monosodium L-glutamate (MSG). By conducting mouse behavioral studies (the 48-h 2-bottle preference test and the conditioned taste aversion test) and assessing gustatory nerve responses, we investigated the taste characteristics of unique umami substances, including sodium succinate, L-theanine, betaine, and the enantiomer of MSG, D-MSG. Furthermore, we examined the synergy of umami with inosine 5'-monophoshate (IMP). In the case of the mice, sodium succinate had an umami taste and showed strong synergy with IMP. L-theanine showed synergy with IMP but did not have an umami taste without IMP. In contrast, betaine did not have an umami taste or synergy with IMP. D-MSG might have weak synergy with IMP.     

Development of an Umami Taste Sensitivity Test and Its Clinical Use

There is a close relationship between perception of umami, which has become recognized as the fifth taste, and the human physical condition. We have developed a clinical test for umami taste sensitivity using a filter paper disc with a range of six monosodium glutamate (MSG) concentrations. We recruited 28 patients with taste disorders (45–78 years) and 184 controls with no taste disorders (102 young [18–25 years] and 82 older [65–89 years] participants). Filter paper discs (5 mm dia.) were soaked in aqueous MSG solutions (1, 5, 10, 50, 100 and 200 mM), then placed on three oral sites innervated by different taste nerves. The lowest concentration participants correctly identified was defined as the recognition threshold (RT) for MSG. This test showed good reproducibility for inter- and intra-observer variability. We concluded that: (1) The RT of healthy controls differed at measurement sites innervated by different taste nerves; that is, the RT of the anterior tongue was higher than that of either the posterior tongue or the soft palate in both young and older individuals. (2) No significant difference in RT was found between young adults and older individuals at any measurement site. (3) The RT of patients with taste disorders was higher before treatment than that of the healthy controls at any measurement site. (4) The RT after treatment in these patients improved to the same level as that of the healthy controls. (5) The cutoff values of RT, showing the highest diagnostic accuracy (true positives + true negatives), were 200 mM MSG for AT and 50 mM MSG for PT and SP. The diagnostic accuracy at these cutoff values was 0.92, 0.87 and 0.86 for AT, PT and SP, respectively. Consequently, this umami taste sensitivity test is useful for discriminating between normal and abnormal umami taste sensations.     

Taste preference synergy between glutamate receptor agonists and inosine monophosphate in rats

Monosodium glutamate (MSG) elicits a taste called umami and interacts synergistically with nucleotide monophosphates such as 5'-inosine monophosphate (IMP) to potentiate this taste intensity. Indeed, the synergistic interaction of nucleotide monophosphates and MSG is a hallmark of umami. We examined interactions between MSG and other taste stimuli, including IMP, by measuring the lick rates of non-deprived rats during 30 s trials. To control for non-linear psychophysical functions, the concentration of one taste stimulus in a binary mixture was systematically increased while the concentration of the second taste stimulus was decreased (stimulus substitution method). Synergy between two stimuli was detected if the lick rate for a binary mixture exceeded that expected from the sum of the lick rates for each stimulus alone. In initial experiments, taste synergy was observed when rats were presented with mixtures of MSG and IMP but not with mixtures of MSG and sucrose. In subsequent experiments, glutamate receptor agonists other than MSG were presented with IMP to test for taste synergy. No evidence of synergy was seen when rats were presented with mixtures of IMP and kainic acid or IMP and N:-methyl-D-aspartate. However, taste synergy between IMP and L-AP4, a potent agonist at mGluR4 receptors, was observed. These results suggest that a metabotropic glutamate receptor similar to mGluR4 may be involved in the taste synergy that characterizes umami.     

Monosodium glutamate and sweet taste: discrimination between the tastes of sweet stimuli and glutamate in rats

Generalization of a conditioned taste aversion (CTA) is based on similarities in taste qualities shared by the aversive substance and another taste substance. CTA experiments with rats have found that an aversion to a variety of sweet stimuli will cross-generalize with monosodium glutamate (MSG) when amiloride, a sodium channel blocker, is added to all solutions to reduce the taste of sodium. These findings suggest that the glutamate anion elicits a sweet taste sensation in rats. CTA experiments, however, generally do not indicate whether two substances have different taste qualities. In this study, discrimination methods in which rats focused on perceptual differences were used to determine if they could distinguish between the tastes of MSG and four sweet substances. As expected, rats readily discriminated between two natural sugars (sucrose, glucose) and two artificial sweeteners (saccharin, SC45647). Rats also easily discriminated between MSG and glucose, saccharin and, to a lesser extent, SC45647 when the taste of the sodium ion of MSG was reduced by the addition of amiloride to all solutions, or the addition of amiloride to all solutions and NaCl to each sweet stimulus to match the concentration of Na+ in the MSG solutions. In contrast, reducing the cue function of the Na+ ion significantly decreased their ability to discriminate between sucrose and MSG. These results suggest that the sweet qualities of glutamate taste is not as dominate a component of glutamate taste as CTA experiments suggest and these qualities are most closely related to the taste qualities of sucrose. The findings of this study, in conjunction with other research, suggest that sweet and umami afferent signaling may converge through a taste receptor with a high affinity for glutamate and sucrose or a downstream transduction mechanism. These data also suggest that rats do not necessarily perceive the tastes of these sweet stimuli as similar and that these sweet stimuli are detected by multiple sweet receptors.     

The taste of monosodium glutamate (MSG), L-aspartic acid, and N-methyl-D-aspartate (NMDA) in rats: are NMDA receptors involved in MSG taste?

Monosodium glutamate (MSG) is believed to elicit a unique taste perception known as umami. We have used conditioned taste aversion assays in rats to compare taste responses elicited by the glutamate receptor agonists MSG, L-aspartic acid (L-Asp), and N-methyl-D-aspartate (NMDA), and to determine if these compounds share a common taste quality. This information could shed new light upon the receptor mechanisms of glutamate taste transduction. Taste aversions to either MSG, L-Asp or NMDA were produced by injecting rats with LiCl after they had ingested one of these stimuli. Subsequently, rats were tested to determine whether they would ingest any of the above compounds. The results clearly show that a conditioned aversion to MSG generalized to L-Asp in a dose-dependent manner. Conversely, rats conditioned to avoid L-Asp also avoided MSG. Conditioned aversions to MSG or L-Asp generalized to sucrose when amiloride was included in all solutions. Importantly, aversions to MSG or L-Asp did not generalize to NMDA, NaCl or KCl, and aversions to NMDA did not generalize to MSG, L-Asp, sucrose or KCl. These data indicate that rats perceive MSG and L-Asp as similar tastes, whereas NMDA, NaCl and KCl elicit other tastes. The results do not support a dominant role for the NMDA subtype of glutamate receptors in taste transduction for MSG (i.e. umami) in rats.     

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.     

Responses to Apical and Basolateral Application of Glutamate in Mouse Fungiform Taste Cells with Action Potentials

In taste bud cells, glutamate may elicit two types of responses, as an umami tastant and as a neurotransmitter. Glutamate applied to apical membrane of taste cells would elicit taste responses whereas glutamate applied to basolateral membrane may act as a neurotransmitter. Using restricted stimulation to apical or basolateral membrane of taste cells, we examined responses of taste cells to glutamate stimulation, separately. Apical application of monosodium glutamate (MSG, 0.3 M) increased firing frequency in some of mouse fungiform taste cells that evoked action potentials. These cells were tested with other basic taste compounds, NaCl (salty), saccharin (sweet), HCl (sour), and quinine (bitter). MSG-sensitive taste cells could be classified into sweet-best (S-type), MSG-best (M-type), and NaCl or other electrolytes-best (N- or E/H-type) cells. Furthermore, S- and M-type could be classified into two sub-types according to the synergistic effect between MSG and inosine-5′-monophosphate (S1, M1 with synergism; S2, M2 without synergism). Basolateral application of glutamate (100 μM) had almost no effect on the mean spontaneous firing rates in taste cells. However, about 10% of taste cells tested showed transient increases in spontaneous firing rates (>mean + 2 standard deviation) after basolateral application of glutamate. These results suggest the existence of multiple types of umami-sensitive taste cells and the existence of glutamate receptor(s) on the basolateral membrane of a subset of taste cells.     

Sucrose and monosodium glutamate taste thresholds and discrimination ability of T1R3 knockout mice

Molecular and behavioral studies have identified heterodimers of the T1R family as receptors for detecting the tastes of sweet (T1R2 + T1R3) and umami (T1R1 + T1R3). However, behavioral studies have reported conflicting findings with T1R3 knockout (KO) mice. One study showed a complete or nearly complete loss of preference for sweet and umami substances by KO mice, whereas KO mice in another study showed only a partial reduction in preferences for sucrose and monosodium glutamate (MSG), the prototypical umami substance. The present experiments used psychophysical methods to assess how sensitive T1R1-KO mice are to sucrose and MSG and discrimination methods to determine if these mice could distinguish between the tastes of sucrose and MSG. Detection thresholds of T1R3-KO mice and wild-type (WT) C57Bl mice were nearly identical for sucrose and MSG. Mice of both genotypes were easily able to discriminate between the tastes of sucrose and MSG. When amiloride (a sodium channel blocker) was added to all solutions to reduce the taste of Na+, discrimination accuracy of both genotypes of mice decreased but more so for the T1R3-KO mice than the WT mice. However, even when the sodium taste of MSG was neutralized, both genotypes could still discriminate between the two substances well above chance performance. These results suggest that sucrose and MSG can be detected by taste receptors other than T1R2 + T1R3 and T1R1 + T1R3 and that the conflicts between the previous studies may have been due to the methodological limitations.     

Flavor Characteristics of Glutathione in Raw and Cooked Foodstuffs

The flavor of glutathione (γ-l-glutamyl-l-cysteinylglycine, GSH) was examined by several sensory evaluations. The measurement of a point of subjective equality (PSE) showed that the peptide increases the flavor characteristics but did not affect the intensity of basic tastes, such as sweetness, saltiness, sourness, and umami. However, the threshold value of GSH decreased significantly in an umami solution containing 0.05% each of monosodium glutamate (MSG) and disodium inosinate (IMP). This suggests that GSH interacts with the umami substance and has a certain effect on the flavor.

GSH had a characteristic kokumi flavor, such as continuity, mouthfulness, and thickness in the umami solution as well as in a model beef extract constructed from analyzed components at a concentration of 0.02% w/v. Some foodstuffs, including meat, were found to contain GSH above its threshold value, which implicates the contribution of GSH to the flavor.

The thermal degradation study suggested that a part of GSH have changed into its disulfide, pyroglutamic acid (PCA), and cyclocysteinylglycine in cooked foodstuffs.     

Isolation and identification of the umami enhancing compounds in Japanese soy sauce

To clarify the key compounds that account for the umami taste of soy sauce, a typical Japanese soy sauce, Koikuchi Shoyu, was separated by preparative chromatography, and the umami enhancing fractions were screened on the basis of an umami intensity of a 6.0 mM monosodium L-glutamate (MSG) solution. Liquid chromatography-time of flight mass spectrometry (LC-TOFMS), 1D/2D nuclear magnetic resonance spectroscopy (NMR) studies of the umami enhancing fractions led to the identification of N-(1-deoxy-D-fructos-1-yl)pyroglutamic acid (Fru-pGlu), N-(1-deoxy-D-fructos-1-yl)valine (Fru-Val), N-(1-deoxy-D-fructos-1-yl)methionine (Fru-Met), pyroglutamylglutamine (pGlu-Gln), and pyroglutamylglycine (pGlu-Gly). Although all the compounds identified were at sub-threshold concentrations in the soy sauce, a taste reconstitution experiment revealed that they contributed part of the umami taste of the soy sauce.