Sour taste finds closure in a potassium channel

Identification of flavor peptides based on virtual screening and molecular docking from Hypsizygus marmoreuss

Hypsizygus marmoreuss is an under-explored source of flavor peptides that can enhance the flavor of NaCl or MSG, allowing products to be reformulated in line with reduction policies. This study utilized advanced techniques, including UPLC-Q-TOF MS/MS and molecular docking, to identify H. marmoreuss peptides. Sensory evaluations revealed 10 peptides with pronounced umami flavors and seven with dominantly salty tastes. VLPVPQK scored highest for umami intensity (5.2), and EGNPAHQK for salty intensity (6.2). Further investigation influenced by 0.35 % MSG or 0.35 % NaCl exposed peptides with elevated umami and salty thresholds. LDSPATPEK, VVEGEPSLK, and QKLPEKPER had umami-enhancing thresholds of 0.18, 0.18, and 0.35 mM, while LDSPATPEK and VVEGEPSLK had similar thresholds for salt (0.09 mM). Molecular docking revealed that taste receptor proteins interacted with umami peptides through hydrogen, carbon-hydrogen, alkyl, and van der Waals forces. Specific amino acids in the umami receptor T1R1 had roles in bonding with umami peptides through hydrogen and carbon-hydrogen interactions. In conclusion, molecular docking proved to be an effective and efficient method for flavor peptide screening. Further, this study demonstrated that flavor peptides from H. marmoreuss had the capacity to enhance NaCl and MSG flavours and might be useful tools for reformulation, reducing salt and MSG contents.

Contrasting Patterns of Gene Duplication, Relocation, and Selection Among Human Taste Genes

In humans, taste genes are responsible for perceiving at least 5 different taste qualities. Human taste genes’ evolutionary mechanisms need to be explored. We compiled a list of 69 human taste-related genes and divided them into 7 functional groups. We carried out comparative genomic and evolutionary analyses for these taste genes based on 8 vertebrate species. We found that relative to other groups of human taste genes, human TAS2R genes have a higher proportion of tandem duplicates, suggesting that tandem duplications have contributed significantly to the expansion of the human TAS2R gene family. Human TAS2R genes tend to have fewer collinear genes in outgroup species and evolve faster, suggesting that human TAS2R genes have experienced more gene relocations. Moreover, human TAS2R genes tend to be under more relaxed purifying selection than other genes. Our study sheds new insights into diverse and contrasting evolutionary patterns among human taste genes.

Mechanisms for the Sour Taste

Sour, the taste of acids, provides important sensory information to prevent the ingestion of unripe, spoiled, or fermented foods. In mammals, acids elicit disgust and pain by simultaneously activating taste and somatosensory neurons innervating the oral cavity. Early researchers detected electrical activity in taste nerves upon presenting acids to the tongue, establishing this as the bona fide sour taste. Recent studies have made significant contributions to our understanding of the mechanisms underlying acid sensing in the taste receptor cells at the periphery and the neural circuitry that convey this information to the brain. In this chapter, we discuss the characterization of sour taste receptor cells, the twists and turns eventually leading to the identification of Otopetrin1 (OTOP1) as the sour taste receptor, the pathway of sour taste signaling from the tongue to the brainstem, and other roles sour taste receptor cells play in the taste bud.

Perceptual Quality of Nonesterified Fatty Acids Varies with Fatty Acid Chain Length

Nonesterified fatty acids (NEFA) are effective taste stimuli. The quality they impart has not been well characterized. Sourness, and "fattiness" have been reported, but an irritation component has also been described and how these transition with gradations of aliphatic chain length has not been systematically studied. This study examined intensity and quality ratings of NEFA ranging from C2 to C18. Oral sites and the time course of sensations were also monitored. Given all NEFA contain carboxylic acid moieties capable of donating hydrogen ions, the primary stimulus for sour taste, testing was conducted with and without sour adaptation to explore the contribution of sour taste across the range of NEFA. Short-chain NEFA (C2-C6) were rated as predominantly sour, and this was diminished in C2 and C4 by sour adaptation. Medium-chain NEFA (C8-C12) were rated as mainly irritating with long-chain NEFA (C18) described mostly as bitter. The latter may reflect the lack of "fatty" lexicon to describe the sensation. Short-chain NEFA were mostly localized to the anterior tongue and were of rapid onset. The sensation from medium-chain NEFA was attributed to the lateral tongue, whereas medium- and long-chain NEFA sensations were predominantly localized to the back of the tongue and throat and had a longer lag time. The findings indicate there is a systematic transition of NEFA taste quality and irritation with increments in chain length and this is consistent with multiple modes of transduction.

Objective gustatory and olfactory dysfunction in COVID-19 patients: a prospective cross-sectional study

PURPOSE

To determine the prevalence of objective gustatory (GD) and olfactory (OD) dysfunction in COVID-19 patients.

METHODS

This is a prospective, cross-sectional study of 51 COVID-19 positive patients diagnosed using RT-PCR-based testing. Of these study participants, 41 reported having present GD and OD at the time of enrollment and ten patients were without symptomatic OD and GD. All participants were objectively tested for OD by Brief Smell Identification Test (BSIT) and for GD by Burghart taste strip test, which were mailed to the participants. The subjective presence and severity of COVID-19 symptoms of smell loss, loss of taste, nasal obstruction, rhinorrhea/mucus production, fever, cough and shortness of breath were also assessed.

RESULTS

Of the 41 patients with GD and OD, only 25.6% (10/39; p ≤ 0.0001) objectively presented GD and 39.1% (16/41; p ≤ 0.0001) OD at the time of their subjective dysfunction. Regarding GD, 23.1% (9/39) suffered from total hypogeusia, 2.6% (1/39) from ageusia. A significant loss of sour (33.3% (13/39)) and salty taste (17.9% (7/39)) could be recognized. Only 10.3% (4/39) showed a reduction in sweet and bitter taste. Concerning OD, 9.8% (4/41) showed a deficit relative to younger age in the BSIT and 29.3% (12/41) results abnormal relative to age.

CONCLUSION

Subjective and objective findings in GD and OD differ significantly. Most patients suffering from objective dysgeusia present a deficit in sour and salty taste.

TRIAL REGISTRATION NUMBER

DRKS00021516; 22/04/2020.

Clinical Role of Extraoral Bitter Taste Receptors

Humans can recognise five basic tastes: sweet, sour, salty, bitter and umami. Sour and salty substances are linked to ion channels, while sweet, bitter and umami flavours are transmitted through receptors linked to the G protein (G protein-coupled receptors; GPCRs). There are two main types of GPCRs that transmit information about sweet, umami and bitter tastes-the Tas1r and TAS2R families. There are about 25 functional TAS2R genes coding bitter taste receptor proteins. They are found not only in the mouth and throat, but also in the intestines, brain, bladder and lower and upper respiratory tract. The determination of their purpose in these locations has become an inspiration for much research. Their presence has also been confirmed in breast cancer cells, ovarian cancer cells and neuroblastoma, revealing a promising new oncological marker. Polymorphisms of TAS2R38 have been proven to have an influence on the course of chronic rhinosinusitis and upper airway defensive mechanisms. TAS2R receptors mediate the bronchodilatory effect in human airway smooth muscle, which may lead to the creation of another medicine group used in asthma or chronic obstructive pulmonary disease. The discovery that functionally compromised TAS2R receptors negatively impact glucose homeostasis has produced a new area of diabetes research. In this article, we would like to focus on what facts have been already established in the matter of extraoral TAS2R receptors in humans.

Characterizing Dysgeusia in Hemodialysis Patients

Dysgeusia (abnormal taste) is common in those with chronic kidney disease and contributes to poor nutritional intake. Previous sensory work has shown that taste improves after dialysis sessions. The goal of this pilot study was to characterize altered taste perceptions in patients on dialysis compared with healthy adults, and to evaluate relationships between serum parameters with taste perceptions. We hypothesized that patients undergoing dialysis would experience blunted taste intensities compared with controls, and that serum levels of potential tastants would be inversely related to taste perception of compounds. Using a cross-sectional design, we carried out suprathreshold sensory assessments (flavor intensity and liking) of tastants/flavors potentially influenced by kidney disease and/or the dialysis procedure. These included sodium chloride, potassium chloride, calcium chloride, sodium phosphate, phosphoric acid, urea, ferrous sulfate, and monosodium glutamate. Individuals on maintenance hemodialysis (n= 17, 10 males, range 23-87 years) were compared with controls with normal gustatory function (n=29, 13 males, range 21-61 years). Unadjusted values for intensity and liking for the solutions showed minimal differences. However, when values were adjusted for participants' perceptions of water (as a control for taste abnormalities), intensity of monosodium glutamate, sodium chloride, and sodium phosphate solutions were more intense for patients on dialysis compared with controls. Some significant correlations were also observed between serum parameters, particularly potassium, for dialysis patients and sensory ratings. These results suggest altered taste perception in patients during dialysis warrants further study.

Genetic Differences in Taste Receptors: Implications for the Food Industry

Inborn genetic differences in chemosensory receptors can lead to differences in perception and preference for foods and beverages. These differences can drive market segmentation for food products as well as contribute to nutritional status. This knowledge may be essential in the development of foods and beverages because the sensory profiles may not be experienced in the same way across individuals. Rather, distinct consumer groups may exist with different underlying genetic variations. Identifying genetic factors associated with individual variability can help better meet consumer needs through an enhanced understanding of perception and preferences. This review provides an overview of taste and chemesthetic sensations and their receptors, highlighting recent advances linking genetic variations in chemosensory genes to perception, food preference and intake, and health. With growing interest in personalized foods, this information is useful for both food product developers and nutrition health professionals alike.

Sour Sensing from the Tongue to the Brain

The ability to sense sour provides an important sensory signal to prevent the ingestion of unripe, spoiled, or fermented foods. Taste and somatosensory receptors in the oral cavity trigger aversive behaviors in response to acid stimuli. Here, we show that the ion channel Otopetrin-1, a proton-selective channel normally involved in the sensation of gravity in the vestibular system, is essential for sour sensing in the taste system. We demonstrate that knockout of Otop1 eliminates acid responses from sour-sensing taste receptor cells (TRCs). In addition, we show that mice engineered to express otopetrin-1 in sweet TRCs have sweet cells that also respond to sour stimuli. Next, we genetically identified the taste ganglion neurons mediating each of the five basic taste qualities and demonstrate that sour taste uses its own dedicated labeled line from TRCs in the tongue to finely tuned taste neurons in the brain to trigger aversive behaviors.

Sour Promotes Risk-Taking: An Investigation into the Effect of Taste on Risk-Taking Behaviour in Humans

Taking risks is part of everyday life. Some people actively pursue risky activities (e.g., jumping out of a plane), while others avoid any risk (e.g., people with anxiety disorders). Paradoxically, risk-taking is a primitive behaviour that may lead to a happier life by offering a sense of excitement through self-actualization. Here, we demonstrate for the first time that sour - amongst the five basic tastes (sweet, bitter, sour, salty, and umami) - promotes risk-taking. Based on a series of three experiments, we show that sour has the potential to modulate risk-taking behaviour across two countries (UK and Vietnam), across individual differences in risk-taking personality and styles of thinking (analytic versus intuitive). Modulating risk-taking can improve everyday life for a wide range of people.

Extraoral Taste Receptor Discovery: New Light on Ayurvedic Pharmacology

More and more research studies are revealing unexpectedly important roles of taste for health and pathogenesis of various diseases. Only recently it has been shown that taste receptors have many extraoral locations (e.g., stomach, intestines, liver, pancreas, respiratory system, heart, brain, kidney, urinary bladder, pancreas, adipose tissue, testis, and ovary), being part of a large diffuse chemosensory system. The functional implications of these taste receptors widely dispersed in various organs or tissues shed a new light on several concepts used in ayurvedic pharmacology (dravyaguna vijnana), such as taste (rasa), postdigestive effect (vipaka), qualities (guna), and energetic nature (virya). This review summarizes the significance of extraoral taste receptors and transient receptor potential (TRP) channels for ayurvedic pharmacology, as well as the biological activities of various types of phytochemical tastants from an ayurvedic perspective. The relative importance of taste (rasa), postdigestive effect (vipaka), and energetic nature (virya) as ethnopharmacological descriptors within Ayurveda boundaries will also be discussed.