Dedicated odor-taste stimulation design for fMRI flavor studies.

BACKGROUND: Flavor is a mental representation that results from the brain's integration of at least odor and taste, and fMRI can highlight brain-related areas. However, delivering stimuli during fMRI can be challenging especially when administrating liquid stimuli in supine position. It remains unclear how and when odorants are released in the nose and how to improve odorant release. NEW METHOD: We used a proton transfer reaction mass spectrometer (PTR-MS) to monitor the in vivo release of odorants via the retronasal pathway during retronasal odor-taste stimulation in a supine position. We tested techniques to improve odorant release, including avoiding or delaying swallowing and velum open training (VOT). RESULTS: Odorant release was observed during retronasal stimulation, before swallowing, and in a supine position. VOT did not improve odorant release. Odorant release during stimulation had a latency more optimal for fitting with BOLD timing than after swallowing. COMPARISON WITH EXISTING METHOD(S): Previous in vivo measurements of odorant release under fMRI-like conditions showed that odorant release occurred only after swallowing. On the contrary, a second study found that aroma release could occur before swallowing, but participants were sitting. CONCLUSION: Our method shows optimal odorant release during the stimulation phase, meeting the criteria for high-quality brain imaging of flavor processing without swallowing-related motion artifacts. These findings provide an important advancement in understanding the mechanisms underlying flavor processing in the brain.

Effects of oenological tannins on aroma release and perception of oxidized and non-oxidized red wine: A dynamic real-time in-vivo study coupling sensory evaluation and analytical chemistry.

Addition of oenological tannins claims to have a positive impact on wine stability, protection from oxidation and likely sensory persistence. However, their role on red wine aroma during oxidation is controversial. The present study aims at investigating the effect of addition of oenological tannins on wine flavour (mainly aroma) before and after air exposure. Temporal Dominance of Sensations, a dynamic sensory evaluation, was coupled with a dynamic chemical measurement (nosespace analysis) using a Proton-Transfer-Reaction Mass-Spectrometer connected to the nasal cavity of 17 assessors. Results showed that the oxidation of a non-oaked Pinot Noir red wine decreases the fruity aroma dominance and increases the maderised and prune one. A contextual decrease of the fruity ethyl decanoate and increase of oxidative Strecker aldehydes are observed. Ellagitannins but not proanthocyanidins preserved perception of fruitiness and prevented increase of maderised notes. Moreover, ellagitannins increase the aroma persistence mainly in the non-oxidized wine.

Understanding retention and metabolization of aroma compounds using an in vitro model of oral mucosa.

The mechanism leading to aroma persistence during eating is not fully described. This study aims at better understanding the role of the oral mucosa in this phenomenon. Release of 14 volatile compounds from different chemical classes was studied after exposure to in vitro models of oral mucosa, at equilibrium by Gas-Chromatography-Flame Ionization Detection (GC-FID) and in dynamic conditions by Proton Transfer Reaction- Mass Spectrometry (PTR-MS). Measurements at equilibrium showed that mucosal hydration reduced the release of only two compounds, pentan-2-one and linalool (p < 0.05), and suggested that cells could metabolize aroma compounds from different chemical families (penta-2,3-dione, trans-2-hexen-1-al, ethyl hexanoate, nonan- and decan-2-one). Dynamic analyses for pentan-2-one and octan-2-one evidenced that the constituents of the mucosal pellicle influenced release kinetics differently depending on molecule hydrophobicity. This work suggests that mucosal cells can metabolize aroma compounds and that non-covalent interactions occur between aroma compounds and oral mucosa depending on aroma chemical structure.

Volatile compounds profiling by using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS). The case study of dark chocolates organoleptic differences.

Direct-injection mass spectrometry (DIMS) techniques have evolved into powerful methods to analyse volatile organic compounds (VOCs) without the need of chromatographic separation. Combined to chemometrics, they have been used in many domains to solve sample categorization issues based on volatilome determination. In this paper, different DIMS methods that have largely outperformed conventional electronic noses (e-noses) in classification tasks are briefly reviewed, with an emphasis on food-related applications. A particular attention is paid to proton transfer reaction mass spectrometry (PTR-MS), and many results obtained using the powerful PTR-time of flight-MS (PTR-ToF-MS) instrument are reviewed. Data analysis and feature selection issues are also summarized and discussed. As a case study, a challenging problem of classification of dark chocolates that has been previously assessed by sensory evaluation in four distinct categories is presented. The VOC profiles of a set of 206 chocolate samples classified in the four sensory categories were analysed by PTR-ToF-MS. A supervised multivariate data analysis based on partial least squares regression-discriminant analysis allowed the construction of a classification model that showed excellent prediction capability: 97% of a test set of 62 samples were correctly predicted in the sensory categories. Tentative identification of ions aided characterisation of chocolate classes. Variable selection using dedicated methods pinpointed some volatile compounds important for the discrimination of the chocolates. Among them, the CovSel method was used for the first time on PTR-MS data resulting in a selection of 10 features that allowed a good prediction to be achieved. Finally, challenges and future needs in the field are discussed.

Effect of lactobionic acid on the acidification, rheological properties and aroma release of dairy gels.

The food industry is investigating new technological applications of lactobionic acid (LBA). In the current work, the effect of lactobionic acid on the acidification of dairy gels (pH 5.5 and 6.2), rheological properties using a double compression test, sodium mobility using (23)Na NMR technique and aroma release using headspace GC-FID were studied. Our results showed that it is possible to use LBA as an alternative to glucono-δ-lactone (GDL) for the production of dairy gels with a controlled pH value. Small differences in the rheological properties and in the amount of aroma volatile organic compounds that were released in the vapour phase, but no significant difference in the sodium ion mobility were obtained. The gels produced with LBA were less firm and released less volatile aroma compounds than the gels produced with GDL. The gels at pH 6.2 were firmer than those at pH 5.5 and had a more organised structure around the sodium ions.

Odorant Metabolism Analysis by an Automated Ex Vivo Headspace Gas-Chromatography Method.

In the olfactory epithelium (OE), odorant metabolizing enzymes have the dual function of volatile component detoxification and active clearance of odorants from the perireceptor environment to respectively maintain the integrity of the tissues and the sensitivity of the detection. Although emphasized by recent studies, this enzymatic mechanism is poorly documented in mammals. Thus, olfactory metabolism has been characterized mainly in vitro and for a limited number of odorants. The automated ex vivo headspace gas-chromatography method that was developed here was validated to account for odorant olfactory metabolism. This method easily permits the measurement of the fate of an odorant in the OE environment, taking into account the odorant gaseous state and the cellular structure of the tissue, under experimental conditions close to physiological conditions and with a high reproducibility. We confirmed here our previous results showing that a high olfactory metabolizing activity of the mammary pheromone may be necessary to maintain a high level of sensitivity toward this molecule, which is critical for newborn rabbit survival. More generally, the method that is presented here may permit the screening of odorants metabolism alone or in mixture or studying the impact of aging, pathology, polymorphism or inhibitors on odorant metabolism.

Combined heterogeneous distribution of salt and aroma in food enhances salt perception.

Aroma-taste interactions and heterogeneous spatial distribution of tastants were used as strategies for taste enhancement. This study investigated the combination of these two strategies through the effect of heterogeneous salt and aroma distribution on saltiness enhancement and consumer liking for hot snacks. Four-layered cream-based products were designed with the same total amount of sodium and ham aroma but varied in their spatial distribution. Unflavoured products containing the same amount of salt and 35% more salt were used as references. A consumer panel (n = 82) rated the intensity of salty, sweet, sour, bitter and umami tastes as well as ham and cheese aroma intensity for each product. The consumers also rated their liking for the products in a dedicated sensory session. The results showed that adding salt-associated aroma (ham) led to enhancement of salty taste perception regardless of the spatial distribution of salt and aroma. Moreover, products with a higher heterogeneity of salt distribution were perceived as saltier (p < 0.01), whereas heterogeneity of ham aroma distribution had only a marginal effect on both aroma and salty taste perception. Furthermore, heterogeneous products were well liked by consumers compared to the homogeneous products.

The salt and lipid composition of model cheeses modifies in-mouth flavour release and perception related to the free sodium ion content.

Reducing salt and lipid levels in foodstuffs without any effect on acceptability is a major challenge, particularly because of their interactions with other ingredients. This study used a multimodal approach to understand the effects of changes to the composition of model cheeses (20/28, 24/24, 28/20 lipid/protein ratios, 0% and 1% added NaCl) on sodium ion mobility ((23)Na NMR), in-mouth sodium release and flavour perception. An increase in the salt content decreased cheese firmness and perceived hardness, and increased sodium ion mobility, in vivo sodium release and both saltiness and aroma perception. With the same amount of salt, a lower lipid/protein ratio increased the firmness of the cheeses, perceived hardness, and decreased sodium ion mobility, in vivo sodium release, saltiness and aroma perception. These findings suggest on one hand that it could be possible to increase saltiness perception by varying cheese composition, thus inducing differences in sodium ion mobility and in free sodium ion concentration, leading to differences in in-mouth sodium release and saltiness perception, and on the other hand that the reformulation of foods in line with health guidelines needs to take account of both salt content and the lipid/protein ratio.

Retention effect of human saliva on aroma release and respective contribution of salivary mucin and α-amylase.

As great differences were observed in the amount of α-amylase in human saliva, there is a need to better understand the effect of this protein alone or in mixture with mucin on aroma compound partitioning. We report the respective role of mucin and α-amylase on the air/liquid partition coefficients of two series of 5 methyl-ketones and 5 ethyl-esters. We confirm that mucin affects the release of aroma compounds and, for the first time, we demonstrate the ability of α-amylase to decrease the release of aroma compounds. For both proteins, we report the involvement of hydrophobic effects. Interestingly, no cumulative effect was observed when both proteins were mixed together in solution. We hypothesize that protein-protein interactions occur between the two proteins and decrease the total number of available binding sites for aroma compounds. The effect of human saliva is also investigated and compared to that of artificial salivas. In the presence of human saliva the release of ketones is lower than in water and slightly higher than in the presence of artificial saliva composed of α-amylase and/or mucin. Esters are more affected by the presence of human saliva than ketones. This observation is due to the presence of an esterase activity in saliva, which activity increases with the hydrophobicity of esters. The difference observed in aroma release between artificial and human salivas could be explained by the presence of other salivary proteins in human saliva.

Structure and composition of model cheeses influence sodium NMR mobility, kinetics of sodium release and sodium partition coefficients.

The mobility and release of sodium ions were assessed in model cheeses with three different lipid/protein ratios, with or without added NaCl. The rheological properties of the cheeses were analysed using uniaxial compression tests. Microstructure was characterised by confocal laser scanning microscopy. (23)Na nuclear magnetic resonance (NMR) spectroscopy was used to study the molecular mobility of sodium ions in model cheeses through measurements of the relaxation and creation times. Greater mobility was observed in cheeses containing a lower protein content and with added NaCl. The kinetics of sodium release from the cheese to an aqueous phase was correlated with the mobility of sodium ions. The highest rates of sodium release were observed with a lower protein content and with added NaCl. The water/cheese partition coefficients of sodium increased when NaCl was added or the protein content was higher. The study highlighted the effect of model cheese characteristics on molecular and macroscopic behaviours of sodium.

Proposed alternative phase ratio variation method for the calculation of liquid-vapour partition coefficients of volatiles.

The phase ratio variation PRV method is a classical way to determine the partition coefficients of volatile compounds between their solution and vapour phases in a variety of circumstances. However, some results obtained by this method can be disappointing. A new PRV equation in which the initial liquid-phase solute concentration is replaced by the liquid-phase solute concentration at equilibrium is proposed. This proposed PRV equation is a second-order polynomial equation. To thoroughly examine the possible modes of calculation, noisy dummy data were generated using both the classical, first-order PRV model (PRV(1)) and the proposed, second-order model (PRV(2)). Thus, pseudo-data obtained from simulations were compared to published experimental data. We observed that the second-order model, PRV(2), produces a lower variability, allowing improved K precision. Moreover, the obtained K(PRV(2)) values are very close to those obtained by classical equilibrium headspace analysis (EHSA). The PRV(2) model we propose responds to the demand for a simple, reliable method and is a useful alternative for the calculation of liquid-vapour partition coefficients.

Retention/release equilibrium of aroma compounds in fat-free dairy gels.

BACKGROUND: The replacement of fat by thickeners in fat-free yogurts leads to an important modification of aroma compound partitioning, with an impact on aroma perception. Investigation of retention/release equilibria allows a good understanding of aroma compound behaviour depending on food composition. RESULTS: Vapour/liquid equilibria of ten aroma compounds (two esters, two ketones, three aldehydes and three alcohols) in several media were studied to investigate the influence of pectin addition to fat-free dairy gel on the retention/release equilibrium. The partition coefficient of each aroma compound was measured by headspace analysis at equilibrium in six media (pure water, low-methoxylated pectin gels and dairy gels with or without added pectin). The release of aroma compounds was similar in the aqueous media (pure water and pectin gels) on the one hand and in the dairy gels on the other hand. However, a trend to greater release occurred with the addition of pectin in both cases. Four aroma compounds were more retained in dairy gels than in water and pectin gels. No relationship appeared between retention and either the chemical function or hydrophobicity (logP values) for the entire set. However, several subsets showed a linear correlation between K and logP values. CONCLUSION: These results suggest that other structural properties than hydrophobicity are probably involved, changing the retention/release behaviour of aroma compounds according to the matrix composition. In order to probe the interactions, further experiments with a larger set of aroma compounds followed by molecular modelling interpretation are needed.

Retention of aroma compounds: an interlaboratory study on the effect of the composition of food matrices on thermodynamic parameters in comparison with water.

BACKGROUND: Partition coefficients give an indication of the retention of aroma compounds by the food matrix. Data in the literature are obtained by various methods, under various conditions and expressed in various units, and it is thus difficult to compare the results. The aim of the present study was first to obtain gas/water and gas/matrix partition coefficients of selected aroma compounds, at different temperatures, in order to calculate thermodynamic parameters and second to compare the retention of these aroma compounds in different food matrices. RESULTS: Yogurts containing lipids and proteins induced a higher retention of aroma compounds than model gel matrices. The observed effects strongly depend on hydrophobicity of aroma compounds showing a retention for ethyl hexanoate and a salting out effect for ethyl acetate. A small but noticeable decrease in enthalpy of affinity is observed for ethyl butyrate and ethyl hexanoate between water and food matrices, suggesting that the energy needed for the volatilization is lower in matrices than in water. CONCLUSION: The composition and complexity of a food matrix influence gas/matrix partition coefficients or aroma compounds in function of their hydrophobicity and to a lower extent enthalpy of vaporization.

Thermodynamic and structure-property study of liquid-vapor equilibrium for aroma compounds.

Thermodynamic parameters (T, DeltaH degrees , DeltaS degrees , K) were collected from the literature and/or calculated for five esters, four ketones, two aldehydes, and three alcohols, pure compounds and compounds in aqueous solution. Examination of correlations between these parameters and the range values of DeltaH degrees and DeltaS degrees puts forward the key roles of enthalpy for vaporization of pure compounds and of entropy in liquid-vapor equilibrium of compounds in aqueous solution. A structure-property relationship (SPR) study was performed using molecular descriptors on aroma compounds to better understand their vaporization behavior. In addition to the role of polarity for vapor-liquid equilibrium of compounds in aqueous solution, the structure-property study points out the role of chain length and branching, illustrated by the correlation between the connectivity index CHI-V-1 and the difference between T and log K for vaporization of pure compounds and compounds in aqueous solution. Moreover, examination of the esters' enthalpy values allowed a probable conformation adopted by ethyl octanoate in aqueous solution to be proposed.

Interactions between beta-lactoglobulin and aroma compounds: different binding behaviors as a function of ligand structure.

Interactions between beta-lactoglobulin (BLG) in its monomeric form and a wide range of aroma compounds were investigated by Fourier transform infrared (FT-IR) and 2D nuclear magnetic resonance (NMR) spectroscopies. A screening of the ligands was carried out by FT-IR through the amide I region changes of BLG upon binding. The location of two binding sites was determined by 2D NMR from the study of 10 selected ligands with different structures. All of the data suggest at least two binding behaviors as a function of the chemical class, the hydrophobicity, or the structure of the ligands. The binding of the elongated aroma compounds, such as 2-nonanone or ethyl pentanoate, within the central cavity involves residues located at the entrance of the calyx and Trp19. The binding onto the protein surface of aroma compounds that have or adopt a compact structure occurs in a site located between strand beta-G, alpha helix, and strand beta-I.

Flavor release from i-carrageenan matrix: a quantitative structure-property relationships approach.

We carried out a QSPR (quantitative structure-property relationships) approach to evaluate the influence of the chemical structure of aqueous matrixes over the partition coefficient between the gas phase and the matrix. The determination of the partition coefficient of flavor ingredients was performed by headspace analysis at equilibrium for both saline solution and i-carrageenan gel. Starting from an initial list of 90 descriptors, we selected 10 descriptors to perform equation generation by the GFA (genetic function approximation) method available in the Cerius2 package. The best obtained equations involve only five descriptors, which encode electronic properties of charges repartition on the molecule (Jurs-RNCS and Dipole-Z) and molecules' shapes (PMI-Y, Shadow-XY, and RadOfGyration), both for saline solution and for i-carrageenan gel. However, the best-fitting equation for carrageenan gel is obtained with a quadratic relation, suggesting that the effect of carrageenan polymers only modulates but does not change the interaction of aroma compounds with water molecules.