Astringency Sensitivity to Tannic Acid: Effect of Ageing and Saliva.

Astringency is an important sensory characteristic of food and beverages containing polyphenols. However, astringency perception in elderly people has not been previously documented. The aim of the present work was to evaluate sensitivity to astringency as a function of age, salivary flow and protein amount. Fifty-four panellists, including 30 elderly people (age = 75 ± 4.2 years) and 24 young people (age = 29.4 ± 3.8 years), participated in this study. Astringency sensitivity was evaluated by the 2-alternative forced choice (2-AFC) procedure using tannic acid solutions. Whole saliva was collected for 5 min before and after the sensory tests. The results showed that the astringency threshold was significantly higher in the elderly group than the young group. No correlation was observed between the salivary protein amount and threshold value. However, a negative correlation between salivary flow and threshold was observed in the young group only. These results showed a difference in oral astringency perception as a function of age. This difference can be linked to salivary properties that differ as a function of age.

Influence of Prebiotic Fructans on Retronasal Aroma from Elderly Individuals.

This study investigates for the first time the role of fructans with prebiotic effects (oligofructose and inulin) on retronasal aroma among elderly individuals. The impact of oligofructose (20% w/w) on retronasal aroma release was investigated using proton transfer reaction-mass spectrometry (PTR-MS) after 73 elderly individuals consumed aqueous solutions aromatized with five aroma compounds (pentan-2-one, nonan-2-one, hexan-2,3-dione, octanal and linalool). The influence of oligofructose and inulin (10% w/w) on the perceived intensity (n = 26) of two aroma descriptors (butter and floral) was also studied together with the possibility of a dumping effect on aroma evaluation due to the sweetness provided by the fructans. The results showed that the presence of oligofructose produced a significant reduction in retronasal aroma release, which could be generally explained by the physicochemical properties of aroma compounds. The presence of prebiotic fructans did not significantly affect the perceived intensity of butter and floral notes, although a dumping effect for the butter descriptor in the presence of oligofructose was observed. To conclude, these findings suggest that although fructans can exert an impact on retronasal aroma, they can be used at precise concentrations to increase the prebiotic fibre content of food products without affecting the aroma profile of foods.

Oral enzymatic detoxification system: Insights obtained from proteome analysis to understand its potential impact on aroma metabolization.

The oral cavity is an entry path into the body, enabling the intake of nutrients but also leading to the ingestion of harmful substances. Thus, saliva and oral tissues contain enzyme systems that enable the early neutralization of xenobiotics as soon as they enter the body. Based on recently published oral proteomic data from several research groups, this review identifies and compiles the primary detoxification enzymes (also known as xenobiotic-metabolizing enzymes) present in saliva and the oral epithelium. The functions and the metabolic activity of these enzymes are presented. Then, the activity of these enzymes in saliva, which is an extracellular fluid, is discussed with regard to the salivary parameters. The next part of the review presents research evidencing oral metabolization of aroma compounds and the putative involved enzymes. The last part discusses the potential role of these enzymatic reactions on the perception of aroma compounds in light of recent pieces of evidence of in vivo oral metabolization of aroma compounds affecting their release in mouth and their perception. Thus, this review highlights different enzymes appearing as relevant to explain aroma metabolism in the oral cavity. It also points out that further works are needed to unravel the effect of the oral enzymatic detoxification system on the perception of food flavor in the context of the consumption of complex food matrices, while considering the impact of food oral processing. Thus, it constitutes a basis to explore these biochemical mechanisms and their impact on flavor perception.

Interactions Between Odorants and Glutathione Transferases in the Human Olfactory Cleft.

Xenobiotic metabolizing enzymes and other proteins, including odorant-binding proteins located in the nasal epithelium and mucus, participate in a series of processes modulating the concentration of odorants in the environment of olfactory receptors (ORs) and finely impact odor perception. These enzymes and transporters are thought to participate in odorant degradation or transport. Odorant biotransformation results in 1) changes in the odorant quantity up to their clearance and the termination of signaling and 2) the formation of new odorant stimuli (metabolites). Enzymes, such as cytochrome P450 and glutathione transferases (GSTs), have been proposed to participate in odorant clearance in insects and mammals as odorant metabolizing enzymes. This study aims to explore the function of GSTs in human olfaction. Using immunohistochemical methods, GSTs were found to be localized in human tissues surrounding the olfactory epithelium. Then, the activity of 2 members of the GST family toward odorants was measured using heterologously expressed enzymes. The interactions/reactions with odorants were further characterized using a combination of enzymatic techniques. Furthermore, the structure of the complex between human GSTA1 and the glutathione conjugate of an odorant was determined by X-ray crystallography. Our results strongly suggest the role of human GSTs in the modulation of odorant availability to ORs in the peripheral olfactory process.

Oxygen K-shell spectroscopy of isolated progressively solvated peptide.

Gas-phase near-edge X-ray-absorption fine structure (NEXAFS) action spectroscopy around the oxygen K-edge and mass spectrometry were employed to probe isolated substance P (SP) molecular ions, both bare and progressively solvated with 4 and 11 water molecules. Detailed mass spectra of bare and hydrated precursors are presented for the resonant photon energy of 532 eV that corresponds to O1s →π(amide)* core excitation, triggering resonant Auger decay and fragmentation from the ionized radical molecular system. The fragmentation pattern of doubly protonated SP hydrated with 4 water molecules clearly shows a series of abundant doubly charged backbone fragments, as well as triply charged precursor with small neutral losses, all preserving full water cluster. This is drastically different from the collisional induced dissociation of the hydrated peptide where the water loss is a dominant relaxation process. Moreover, the action NEXAFS obtained from several resolved small backbone fragments revealed increased fragmentation of hydrated SP relative to the bare one, due to a resonant O1s excitation of the attached water molecules. Such unexpected result inspires further experimental developments to investigate possible nonlocal energy transfer from the solvent to the biomolecules within the first solvation shell. The experiment is supported by molecular dynamics and DFT calculations to estimate the intensity of the resonant X-ray absorption of bare and hydrated SP around peptide and water O1s excitation region.

Nanoscale Mapping of the Physical Surface Properties of Human Buccal Cells and Changes Induced by Saliva.

The mucosal pellicle, also called salivary pellicle, is a thin biological layer made of salivary and epithelial constituents, lining oral mucosae. It contributes to their protection against microbiological, chemical, or mechanical insults. Pellicle formation depends on the cells' surface properties, and in turn the pellicle deeply modifies such properties. It has been reported that the expression of the transmembrane mucin MUC1 in oral epithelial cells improves the formation of the mucosal pellicle. Here, we describe an approach combining classical and functionalized tip atomic force microscopy and scanning microwave microscopy to characterize how MUC1 induces changes in buccal cells' morphology, hydrophobicity, and electric properties to elucidate the physicochemical mechanisms involved in the enhancement of the anchoring of salivary proteins. We show that MUC1 expression did not modify drastically the morphology of the epithelial cells' surface. MUC1 expression, however, resulted in the presence of more hydrophobic and more charged areas at the cell surface. The presence of salivary proteins decreased the highest attractive and repulsive forces recorded between the cell surface and a functionalized hydrophobic atomic force microscopy (AFM) tip, suggesting that the most hydrophobic and charged areas participate in the binding of salivary proteins. The cells' dielectric properties were altered by both MUC1 expression and the presence of a mucosal pellicle. We finally show that in the absence of MUC1, the pellicle appeared as a distinct layer poorly interacting with the cells' surface. This integrative AFM/scanning microwave microscopy approach may usefully describe the surface properties of various cell types, with relevance to the bioadhesion or biomimetics fields.

Assessment Wine Aroma Persistence by Using an in Vivo PTR-ToF-MS Approach and Its Relationship with Salivary Parameters.

To better understand wine aroma persistence, the nasal cavity of nine volunteers was monitored by Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS) after they rinsed their mouths with three rosé wines (one control and the same wine supplemented with two tannin extracts) during four minutes. Wines were aromatised with a mixture of five target aroma compounds. Results showed that wine aroma persistence was highly compound-dependent: while esters disappeared very fast, other compounds such as linalool remained in the oral cavity for longer times after wine expectoration. A low effect of tannins (at 50 mg/L) on nasal cavity parameters was observed, with the exception for the compound ethyl decanoate that was significantly higher released in the presence of tannins. Strong interindividual differences on aroma persistence were also found. Significant positive correlations with the salivary total protein content and negative with the salivary flow were observed for specific compounds. This work has studied for the first time in vivo wine aroma persistence in real time from an analytical perspective.

Impact of TIEG1 on the structural properties of fast- and slow-twitch skeletal muscle.

INTRODUCTION: Transforming growth factor-beta (TGF-ß)-inducible early gene-1 (TIEG1) is a transcription factor that is highly expressed in skeletal muscle. The purpose of this study was to characterize the structural properties of both fast-twitch (EDL) and slow-twitch (soleus) muscles in the hindlimb of TIEG1-deficient (TIEG1-/- ) mice. METHODS: Ten slow and 10 fast muscles were analyzed from TIEG1-/- and wild-type (WT) mice using MRI texture (MRI-TA) and histological analyses. RESULTS: MRI-TA could discriminate between WT slow and fast muscles. Deletion of the TIEG1 gene led to changes in the texture profile within both muscle types. Specifically, muscle isolated from TIEG1-/- mice displayed hypertrophy, hyperplasia, and a modification of fiber area distribution. CONCLUSIONS: We demonstrated that TIEG1 plays an important role in the structural properties of skeletal muscle. This study further implicates important roles for TIEG1 in the development of skeletal muscle and suggests that defects in TIEG1 expression and/or function may be associated with muscle disease. Muscle Nerve 55: 410-416, 2017.

Contribution of synchrotron radiation to photoactivation studies of biomolecular ions in the gas phase.

Photon activation of ions in the visible and ultraviolet range attracts a growing interest, partly for its promising applications in tandem mass spectrometry. However, this task is not trivial, as it requires notably high brilliance photon sources. Hence, most of the work in that field has been performed using lasers. Synchrotron radiation is a source continuously tunable over a wide photon energy range and which possesses the necessary characteristics for ion activation. This review focuses on the array of applications of synchrotron radiation in photon activation of ions ranging from near UV to soft X-rays.

Action spectroscopy of a protonated peptide in the ultraviolet range.

Action spectroscopy of protonated substance P, a model undecapeptide, has been probed from 5.2 eV to 20 eV. For photon energy above the ionization threshold measured at 10.3 ± 0.1 eV, the radical dication is observed along with side chain losses and abundant formation of all kinds of sequence ions. Below the photoionization threshold, the photoproducts involve side chain cleavages and backbone cleavages into a-, b-/y-, and c-sequence ions. Different electronic excited states appear to produce different fragment ions. Norrish type I and II reactions are proposed to account for some photoproducts. This study bridges the gap between laser activation and electron-induced dissociation of peptides. Moreover, our results report for the first time a comprehensive picture of the photochemical fragmentation of a gas phase peptide in a wide photon energy range.

Changes in contractile and elastic properties of the triceps surae muscle induced by neuromuscular electrical stimulation training.

PURPOSE: Neuromuscular electrical stimulation (NMES) training is known to induce improvement in force production capacities and fibre-type transition. The aim of this study was to determine whether NMES training also leads to changes in the mechanical properties of the human triceps surae (TS) muscle. METHODS: Fifteen young male subjects performed a training protocol (4 weeks, 18 sessions, 4-5 sessions per week) based on a high-frequency isometric NMES programme of TS muscle. Quick-release test was used to evaluate Musculo-Tendinous (MT) stiffness index (SIMT) as the slope of the linear MT stiffness-torque relationships under submaximal contraction. Sinusoidal perturbations allowed the assessment of musculo-articular stiffness index (SIMA) as well as the calculation of the maximal angular velocity ([Formula: see text]) of TS muscle using an adaptation of Hill's equation. RESULTS: After NMES training, Maximal Voluntary Contraction under isometric conditions and [Formula: see text] increased significantly by 17.5 and 20.6 %, respectively, while SIMT and SIMA decreased significantly (-12.7 and -9.3 %, respectively). CONCLUSIONS: These changes in contractile and elastic properties may lead to functional changes of particular interest in sport-related activities as well as in the elderly.

Astringency sensitivity to tannic acid: Effect of ageing and salivary proline-rich protein levels.

The link between salivary composition and sensitivity to astringency as a function of age has still not been established. In this work, we propose the hypothesis that ageing leads to changes in the concentration of salivary proline-rich proteins (PRPs), which alters the astringency perception threshold with age. To test this hypothesis, astringency sensitivity to tannic acid and saliva was assessed in 30 elderly people and 24 young people. Basic PRPs (bPRPs) and glycosylated PRPs (gPRPs) were quantified immunochemically via western blot analysis. The results showed that the amounts of bPRPs and gPRPs were similar between the young and elderly groups. However, a positive correlation between the gPRP amount and astringency threshold was observed only in the young group, while a negative correlation between the bPRP amount and astringency threshold was observed only in the elderly group. This finding suggests differences in the contribution of PRP type to astringency perception as a function of age.

Rattus norvegicus Glutathione Transferase Omega 1 Localization in Oral Tissues and Interactions with Food Phytochemicals.

Glutathione transferases are xenobiotic-metabolizing enzymes with both glutathione-conjugation and ligandin roles. GSTs are present in chemosensory tissues and fluids of the nasal/oral cavities where they protect tissues from exogenous compounds, including food molecules. In the present study, we explored the presence of the omega-class glutathione transferase (GSTO1) in the rat oral cavity. Using immunohistochemistry, GSTO1 expression was found in taste bud cells of the tongue epithelium and buccal cells of the oral epithelium. Buccal and lingual extracts exhibited thiol-transferase activity (4.9 ± 0.1 and 1.8 ± 0.1 µM/s/mg, respectively). A slight reduction from 4.9 ± 0.1 to 4.2 ± 0.1 µM/s/mg (p < 0.05; Student's t test) was observed in the buccal extract with 100 µM GSTO1-IN-1, a specific inhibitor of GSTO1. RnGSTO1 exhibited the usual activities of omega GSTs, i.e., thiol-transferase (catalytic efficiency of 8.9 × 104 M-1·s-1), and phenacyl-glutathione reductase (catalytic efficiency of 8.9 × 105 M-1·s-1) activities, similar to human GSTO1. RnGSTO1 interacts with food phytochemicals, including bitter compounds such as luteolin (Ki = 3.3 ± 1.9 µM). Crystal structure analysis suggests that luteolin most probably binds to RnGSTO1 ligandin site. Our results suggest that GSTO1 could interact with food phytochemicals in the oral cavity.

Photodissociation of leucine-enkephalin protonated peptide: an experimental and theoretical perspective.

Understanding the competing processes that govern far ultraviolet photodissociation (FUV-PD) of biopolymers such as proteins is a challenge. Here, we report a combined experimental and theoretical investigation of FUV-PD of protonated leucine-enkephalin pentapeptide ([YGGFL + H]+) in the gas-phase. Time-dependent density functional theory (TD-DFT) calculations in combination with experiments and previous results for amino acids and shorter peptides help in rationalizing the evolution of the excited states. The results confirm that fragmentation of [YGGFL + H]+ results mainly from vibrationally excited species in the ground electronic state, populated after internal conversion. We also propose fragmentation mechanisms for specific photo-fragments such as tyrosine side chain loss (with an extra hydrogen) or hydrogen loss. In general, we observe the same mechanisms as for smaller peptides or protonated Tyr and Phe, that are not quenched by the presence of other amino acids. Nevertheless, we also found some differences, as for H loss, in part due to the fact that the charge is solvated by the peptide chain and not only by the COOH terminal group.

Development of New Models of Oral Mucosa to Investigate the Impact of the Structure of Transmembrane Mucin-1 on the Mucosal Pellicle Formation and Its Physicochemical Properties.

The mucosal pellicle (MP) is a biological film protecting the oral mucosa. It is composed of bounded salivary proteins and transmembrane mucin MUC1 expressed by oral epithelial cells. Previous research indicates that MUC1 expression enhances the binding of the main salivary protein forming the MP, MUC5B. This study investigated the influence of MUC1 structure on MP formation. A TR146 cell line, which does not express MUC1 natively, was stably transfected with genes coding for three MUC1 isoforms differing in the structure of the two main extracellular domains: the VNTR domain, exhibiting a variable number of tandem repeats, and the SEA domain, maintaining the two bound subunits of MUC1. Semi-quantification of MUC1 using dot blot chemiluminescence showed comparable expression levels in all transfected cell lines. Semi-quantification of MUC5B by immunostaining after incubation with saliva revealed that MUC1 expression significantly increased MUC5B adsorption. Neither the VNTR domain nor the SEA domain was influenced MUC5B anchoring, suggesting the key role of the MUC1 N-terminal domain. AFM-IR nanospectroscopy revealed discernible shifts indicative of changes in the chemical properties at the cell surface due to the expression of the MUC1 isoform. Furthermore, the observed chemical shifts suggest the involvement of hydrophobic effects in the interaction between MUC1 and salivary proteins.

Aggregation of the salivary proline-rich protein IB5 in the presence of the tannin EgCG.

In the mouth, proline-rich proteins (PRP), which are major components of stimulated saliva, interact with tannins contained in food. We report in vitro interactions of the tannin epigallocatechin gallate (EgCG), with a basic salivary PRP, IB5, studied through electrospray ionization mass spectrometry (ESI-MS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). In dilute protein (IB5) solutions of low ionic strength (1 mM), the proteins repel each other, and the tannins bind to nonaggregated proteins. ESI-MS experiments determine the populations of nonaggregated proteins that have bound various numbers of tannin molecules. These populations match approximately the Poisson distribution for binding to n = 8 sites on the protein. MS/MS experiments confirm that complexes containing n = 1 to 8 EgCG molecules are dissociated with the same energy. Assuming that the 8 sites are equivalent, we calculate a binding isotherm, with a binding free energy Δµ = 7.26RT(a) (K(d) = 706 µM). In protein solutions that are more concentrated (0.21 mM) and at higher ionic strength (50 mM, pH 5.5), the tannins can bridge the proteins together. DLS experiments measure the number of proteins per aggregate. This number rises rapidly when the EgCG concentration exceeds a threshold (0.2 mM EgCG for 0.21 mM of IB5). SAXS experiments indicate that the aggregates have a core-corona structure. The core contains proteins that have bound at least 3 tannins and the corona has proteins with fewer bound tannins. These aggregates coexist with nonaggregated proteins. Increasing the tannin concentration beyond the threshold causes the transfer of proteins to the aggregates and a fast rise of the number of proteins per aggregate. A poisoned growth model explains this fast rise. Very large cationic aggregates, containing up to 10,000 proteins, are formed at tannin concentrations (2 mM) slightly above the aggregation threshold (0.2 mM).

Photo-induced electron detachment of protein polyanions in the VUV range.

Biomolecular polyanions mainly relax by electron emission after UV excitation. Here, we study photodetachment of protein polyanions in the 6-16 eV VUV range by coupling a linear quadrupole ion trap with a synchrotron beamline. Gas-phase VUV action spectra of electrospray-produced multiply deprotonated insulin (5.6 kDa) and myoglobin (16.7 kDa) proteins are reported, which significantly increases the amount of data available on the optical response of proteins in the VUV. The influence of the protein charge and oxidation state upon the electron detachment efficiency is discussed. For small protein such as insulin, it appears that higher charge states produce higher detachment yields. Investigations on oxidized species show that the nature of the groups bearing the negative charges has an influence on the yields. For larger proteins, comparison of two forms of myoglobin clearly indicate that the three-dimensional structure does not impact much on the shape and the magnitude of the photodetachment spectra, in spite of a slight shift for the first electronic excited states.

Ipsi- and contralateral H-reflexes and V-waves after unilateral chronic Achilles tendon vibration.

Chronic Achilles tendon vibration has previously shown its effectiveness in improving plantar flexor's strength and activation capacities. The present study investigated the related neural mechanisms by analyzing H-reflexes and V-waves of the soleus (SOL) and gastrocnemii (GM gastrocnemius medialis; GL gastrocnemius lateralis) muscles under maximal isometric plantar flexion. Moreover, recordings were conducted bilaterally to address potential crossed effects. 11 subjects were engaged in this study. Maximal voluntary contraction and superimposed H-reflexes and V-waves were quantified in both legs at baseline (PRE) and 2 weeks later to verify repeatability of data (CON). Then, subjects were retested after 14 days of daily unilateral Achilles tendon vibration (VIB; 1 h per day; frequency: 50 Hz). No changes were reported between PRE and CON data. In the VIB condition, there was an increase in MVC for both the vibrated (+9.1 %; p = 0.016) and non-vibrated (+10.2 %; p = 0.009) legs. The H-reflex increased by a mean 25 % in the vibrated SOL (p < 0.001), while it remained unchanged for the contralateral side (p = 0.531). The SOL V-wave also increased in the vibrated limb (+43.3 %; p < 0.001), as well as in the non-vibrated one (+41.9 %; p = 0.006). Furthermore, the GM V-wave increased by 37.8 % (p = 0.081) in the vibrated side and by 39.4 % (p = 0.03) in the non-vibrated side. However, no changes were reported for the GL muscles. While the present study confirmed the strength gains induced by chronic Achilles tendon vibration, the results indicated a cross-education phenomenon with differences in neural adaptations between the vibrated leg and non-vibrated leg.

Role of Insect and Mammal Glutathione Transferases in Chemoperception.

Glutathione transferases (GSTs) are ubiquitous key enzymes with different activities as transferases or isomerases. As key detoxifying enzymes, GSTs are expressed in the chemosensory organs. They fulfill an essential protective role because the chemosensory organs are located in the main entry paths of exogenous compounds within the body. In addition to this protective function, they modulate the perception process by metabolizing exogenous molecules, including tastants and odorants. Chemosensory detection involves the interaction of chemosensory molecules with receptors. GST contributes to signal termination by metabolizing these molecules. By reducing the concentration of chemosensory molecules before receptor binding, GST modulates receptor activation and, therefore, the perception of these molecules. The balance of chemoperception by GSTs has been shown in insects as well as in mammals, although their chemosensory systems are not evolutionarily connected. This review will provide knowledge supporting the involvement of GSTs in chemoperception, describing their localization in these systems as well as their enzymatic capacity toward odorants, sapid molecules, and pheromones in insects and mammals. Their different roles in chemosensory organs will be discussed in light of the evolutionary advantage of the coupling of the detoxification system and chemosensory system through GSTs.

Unlocking Flavor Potential Using Microbial ß-Glucosidases in Food Processing.

Aroma is among of the most important criteria that indicate the quality of food and beverage products. Aroma compounds can be found as free molecules or glycosides. Notably, a significant portion of aroma precursors accumulates in numerous food products as nonvolatile and flavorless glycoconjugates, termed glycosidic aroma precursors. When subjected to enzymatic hydrolysis, these seemingly inert, nonvolatile glycosides undergo transformation into fragrant volatiles or volatiles that can generate odor-active compounds during food processing. In this context, microbial ß-glucosidases play a pivotal role in enhancing or compromising the development of flavors during food and beverage processing. ß-glucosidases derived from bacteria and yeast can be utilized to modulate the concentration of particular aroma and taste compounds, such as bitterness, which can be decreased through hydrolysis by glycosidases. Furthermore, oral microbiota can influence flavor perception by releasing volatile compounds that can enhance or alter the perception of food products. In this review, considering the glycosidic flavor precursors present in diverse food and beverage products, we underscore the significance of glycosidases with various origins. Subsequently, we delve into emerging insights regarding the release of aroma within the human oral cavity due to the activity of oral microbial glycosidases.