Retronasal Aroma of Beef Pate Analyzed by a Chewing Simulator.

In retronasal aroma, the targeted aroma compounds are released from food during chewing. The changes in the food structures during chewing strongly influence the release of the compounds, therefore affecting the perception of food. Here, the relationship between retronasal aroma and food deliciousness based on the physicochemical properties of aroma compounds was examined. We considered the consumption of solid foods and the effect of oral parameters in elderly people. Beef pate was used as a model food sample to study the effect of the release of aroma compounds under controlled in vitro mastication and salivation conditions using a chewing simulator. We identified the effects of coexisting ingredients such as beef fat on the time course behavior of the release of aroma compounds. In particular, the release of the middle types of aromas was significantly faster with stronger chewing force, and higher with a high fat content of the sample. In addition, a larger release intensity was observed when soy proteins were partially substituted for beef proteins. Using an appropriate model saliva, a change in the salting-out effect from the saliva composition was found to be a factor, which could explain the lowering of aroma sensation in an elderly person.

Salt and Aroma Compound Distributions Influence Flavour Release and Temporal Perception While Eating Hot-Served Flans.

To counteract the negative effect of salt overconsumption on health, strategies have been developed to reduce the salt content in food products. Among them, two promising strategies based on odour-induced saltiness enhancement and the heterogeneous distribution of flavour compounds were combined and assessed in four-layer cream-based snacks. To investigate the relationship between saltiness enhancement, temporal release and perception of flavour compounds in hot snacks with heterogeneous distribution of salt and aroma compounds, complementary techniques were used: nose space PTR-Tof-MS (Proton Transfer Reaction-Time of Flight-Mass Spectrometry) to assess the release of aroma compounds in vivo, and ATI (Alternate Time-Intensity) and TDS Temporal Dominance of Sensations) to evaluate perception as a function of time. The obtained results confirmed that the strategy of concentrating salt in the outer layer of a multilayer product was the optimal solution with respect to taste intensity. Heterogeneous salt distribution decreased aroma compound release and consequently aroma intensity but in different ways according to both salt and added aroma distribution in the food matrix. The salty taste enhancement could be due to the initial strong dominance of the salty sensation at the very beginning of the eating process. The involved mechanisms rely on a combination of physico-chemical and perceptual effects which are not clear yet.

Trail-Following Pheromones in the Termite Subfamily Syntermitinae (Blattodea, Termitoidae, Termitidae).

Trail-following behavior is a key to ecological success of termites, allowing them to orient themselves between the nesting and foraging sites. This behavior is controlled by specific trail-following pheromones produced by the abdominal sternal gland occurring in all termite species and developmental stages. Trail-following communication has been studied in a broad spectrum of species, but the "higher" termites (i.e. Termitidae) from the subfamily Syntermitinae remain surprisingly neglected. To fill this gap, we studied the trail-following pheromone in six genera and nine species of Syntermitinae. Our chemical and behavioral experiments showed that (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol is the single component of the pheromone of all the termite species studied, except for Silvestritermes euamignathus. This species produces both (3Z,6Z)-dodeca-3,6-dien-1-ol and neocembrene, but only (3Z,6Z)-dodeca-3,6-dien-1-ol elicits trail-following behavior. Our results indicate the importance of (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol, the most widespread communication compound in termites, but also the repeated switches to other common pheromones as exemplified by S. euamignathus.

In-mouth mechanisms leading to flavor release and perception.

During eating, foods are submitted to two main oral processes-chewing, including biting and crushing with teeth, and progressive impregnation by saliva resulting in the formation of a cohesive bolus and swallowing of the bolus. Texture influences the chewing behavior, including mastication and salivation, and in turn, these parameters influence texture perception and bolus formation. During this complex mouth process, flavor compounds are progressively released from the food matrix. This phenomenon is mainly dependent on the food texture, the composition and in-mouth breakdown, and on saliva impregnation and activity, but an individual's anatomical and physiological aspects characteristics should also be taken into account. This article reviews the knowledge and progresses on in-mouth processes leading to food breakdown and flavor release and affecting perception. Relationships between food texture and composition, food breakdown, oral physiology, and flavor release are developed and discussed. This review includes not only the mechanical aspects of oral physiology but also the biological aspects such as the influence of saliva composition, activity, and regulation on flavor perception. In vitro and in silico approaches are also described.

Chemical and behavioural characterization of the rabbit mammary pheromone.

Mammals owe part of their evolutionary success to the harmonious exchanges of information, energy and immunity between females and their offspring. This functional reciprocity is vital for the survival and normal development of infants, and for the inclusive fitness of parents. It is best seen in the intense exchanges taking place around the mother's offering of, and the infant's quest for, milk. All mammalian females have evolved behavioural and sensory methods of stimulating and guiding their inexperienced newborns to their mammae, whereas newborns have coevolved means to respond to them efficiently. Among these cues, maternal odours have repeatedly been shown to be involved, but the chemical identity and pheromonal nature of these cues have not been definitively characterized until now. Here we focus on the nature of an odour signal emitted by the female rabbit to which newborn pups respond by attraction and oral grasping, and provide a complete chemical and behavioural description of a pheromone of mammary origin in a mammalian species.

Effect of Oral Physiology Parameters on In-Mouth Aroma Compound Release Using Lipoprotein Matrices: An In Vitro Approach.

Temporal aroma compound release during eating is a function of the physicochemical properties of the food matrix, aroma compounds, and oral physiology of individuals. However, the influence of each parameter on the release of each aroma component should be clarified. Two flavored lipoprotein matrices varying in composition were chewed in a chewing simulator that reproduced most of the physiological functions of the mouth. Aroma compound releases (butanoic acid, 2-heptanone, ethyl butyrate, 3-octanone, and 2-nonanone) were followed in real time by direct connection of the device to APCI-MS (atmospheric pressure chemical ionization mass spectrometry). Each oral parameter was controlled and decoupled using the in vitro device. The food matrix composition had only a low impact on aroma compound release, but the controlled oral parameters had significantly different influences on the release of aroma compounds according to their physicochemical characteristics. The release of certain compounds seemed more sensitive to bite force, while others seemed more sensitive to the shearing angle. The salivary flow rate primarily influenced the more hydrophobic compounds. Significant interactions were also observed between shear angle, salivary flow rate, and lipoprotein matrix composition, mainly for the release of the more hydrophobic volatile compounds; this needs further investigations to be clarified.

Ex vivo real-time monitoring of volatile metabolites resulting from nasal odorant metabolism.

Odorant-metabolizing enzymes are critically involved in the clearance of odorant molecules from the environment of the nasal neuro-olfactory tissue to maintain the sensitivity of olfactory detection. Odorant metabolism may also generate metabolites in situ, the characterization and function of which in olfaction remain largely unknown. Here, we engineered and validated an ex vivo method to measure odorant metabolism in real-time. Glassware containing an explant of rat olfactory mucosa was continuously flushed with an odorant flow and was coupled to a proton transfer reaction-mass spectrometer for volatile compound analysis. Focusing on carboxylic esters and diketone odorants, we recorded the metabolic uptake of odorants by the mucosa, concomitantly with the release of volatile odorant metabolites in the headspace. These results significantly change the picture of real-time in situ odorant metabolism and represent a new step forward in the investigation of the function of odorant metabolites in the peripheral olfactory process. Our method allows the systematic identification of odorant metabolites using a validated animal model and permits the screening of olfactory endogenously produced chemosensory molecules.

Publisher Correction: Ex vivo real-time monitoring of volatile metabolites resulting from nasal odorant metabolism.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

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.

Modified proton transfer reaction mass spectrometry (PTR-MS) operating conditions for in vitro and in vivo analysis of wine aroma.

With proton transfer reaction-mass spectrometry standard operating conditions, analysis of alcoholic beverages is an analytical challenge. Ethanol reacts with the primary ion H3 O+ leading to its depletion and to formation of ethanol-related ions and clusters, resulting in unstable ionization and in significant fragmentation of analytes. Different methods were proposed but generally resulted in lowering the sensitivity and/or complicating the mass spectra. The aim of the present study was to propose a simple, sensitive, and reliable method with fragmentation as low as possible, linearity within a realistic range of volatile organic compounds concentrations, and applicability to in vivo dynamic aroma release (nosespace) studies of wines. For in vitro analyses, a reference flask containing a hydro-alcoholic solution (10% ethanol) was permanently connected to the PTR-MS inlet in order to establish ethanol chemical ionization conditions. A low electric field strength to number density ratio E/N (80 Td) was used in the drift-tube. A stable reagent ion distribution was obtained with the primary protonated ethanol ion C2 H5 OH2+ accounting for more than 80% of the ionized species. The ethanol dimer (C2 H5 OH)2 H+ accounted for only 10%. Fragmentation of some aroma molecules important for white wine flavor (various esters, linalool, cis-rose oxide, 2-methylpropan-1-ol, 3-methylbutan-1-ol, and 2-phenylethanol) was studied from same ethanol content solutions connected alternatively with the reference solution to the instrument inlet. Linear dynamic range and limit of detection (LOD) were determined for ethyl hexanoate. Fragmentation of the protonated analytes was limited to a few ions of low intensity, or to specific fragment ions with no further fragmentation. Association and/or ligand switching reactions from ethanol clusters were only significant for the primary alcohols. Interpretation of the mass spectra was straightforward with easy detection of diagnostic ions. These results made this ethanol ionization method suitable for direct headspace analyses of model wines and to their nosespace analyses.

Quantification of eicosapentaenoic and docosahexaenoic acid geometrical isomers formed during fish oil deodorization by gas-liquid chromatography.

Long-chain polyunsaturated fatty acids (LC-PUFAs) of the n-3 series and especially eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) have important biological properties. The main dietary sources of LC-PUFAs are fish and fish oil. Geometrical isomerization is one of the main reactions happening during the thermal treatment of polyunsaturated fatty acids. Refined fish oils are used to supplement food products in LC-PUFAs and the quality of these nutritional ingredients have to be controlled. In the present study, a suitable method for the quantification of EPA and DHA geometrical isomers in fish oils by gas-liquid chromatography (GC) is presented. A highly polar capillary column (CP-Sil 88, 100 m) operating under optimal conditions was used. Method selectivity was studied by GC-mass spectrometry. The performance characteristics of the quantification method were studied using samples of fish oil deodorized at 220 degrees C for 3 h. The linearity of the method was assessed by analyzing composite samples obtained by mixing fish oil deodorized at 220 degrees C with semi-refined fish oil (control). Precision was evaluated by analyzing the same samples in triplicate. Results showed that the validated method is suitable to quantify low amounts of geometrical (trans) isomers of EPA and DHA in refined fish oils. The limits of quantification of the EPA and DHA geometrical isomers are 0.16 and 0.56 g/100 g of fish oil, for EPA and DHA, respectively. Commercially available LC-PUFA oil samples were evaluated by using the validated method. The results show that the oils analyzed contain low amounts (<1% of total fatty acids) of geometrical isomers of EPA and DHA.

Impact of hardness of model fresh cheese on aroma release: in vivo and in vitro study.

Using atmospheric pressure chemical ionization-mass spectrometry, aroma release was investigated in vivo and in vitro from three cheese-like gels with different hardnesses. In vivo, nosespace experiments were performed with 14 subjects. Results showed that the harder gel induced a greater and a faster release of all aroma compounds. In vitro, aroma release was followed in a mouth simulator where breakdown was mechanically produced. The same rate of stirring was applied to the three gels. In these conditions, we found that the amount of aroma released from the three gels was not discriminant. Thus, modification of gel structure had a strong impact on in vivo aroma release, but structural variations alone were not sufficient to induce a greater release. Natural breakdown provided by panelists during food consumption and adapted to the texture of the food was proposed to be the key parameter affecting in vivo aroma release.

Impact of destroying the structure of model gels on volatile release.

The release of a strawberry aroma from different composite gels taken as models of fruit preparations and from a sucrose solution was investigated. The composition of the model systems differed with regard to the gelling agent, either pectin or carrageenan, and to the rigidity of the gel. With the use of atmospheric pressure chemical ionization-mass spectrometry, the release profiles of the aroma compounds were determined under stirring. At the same time, purge and trap measurements were performed to determine the release profiles of the aroma compounds without stirring. The comparison of the patterns obtained using these two complementary methods made it possible to determine how the structure of the matrix, the mechanical treatment, and the properties of the aroma compound affect aroma release. A far greater proportion of the aroma compounds was retained in the fruit preparation systems than in the sucrose solution. The different release profiles could be interpreted in terms of the volatility of the aroma compounds and of their diffusion through the gels.

Flavored yogurt complex viscosity influences real-time aroma release in the mouth and sensory properties.

The influence of flavored yogurt texture on aroma perception and in-nose aroma release measured by atmospheric pressure chemical ionization mass spectrometry analysis was investigated. The study was carried out on six yogurts varied by protein composition and mechanical treatment. For the same matrix composition, the complex viscosity of yogurts influenced in-nose release and perception. After swallowing, aroma release and intensity of olfactory perception were stronger in low-viscosity yogurts than in high-viscosity yogurts. Moreover, the protein composition influenced aroma release only when yogurts exhibited wide variations of complex viscosity and consequently texture. In mouth, aroma release and perception were influenced more by yogurt mechanical treatment than by protein composition. On the basis of mass transfer analysis, the main physical mechanism which could explain the difference in aroma release would be the surface exchange area developed in the mouth and in the throat.

Methylthioacetaldehyde, a possible intermediate metabolite for the production of volatile sulphur compounds from L-methionine by Lactococcus lactis.

Volatile sulphur compounds (VSCs) production from L-methionine was studied in Lactococcus lactis. In vitro studies with radiolabelled L-methionine and resting cells of L. lactis revealed that L-methionine was initially converted to alpha-keto-gamma-methylthiobutyrate (KMBA) by a transamination reaction. A part of KMBA was subsequently chemically converted to methylthioacetaldehyde, methanethiol and dimethylsulphides. Chemical conversion of KMBA to methylthioacetaldehyde was dependent on pH, Mn(II) and oxygen. Since methanethiol and dimethylsulphide production was highly related to that of methylthioacetaldehyde, the latter compound was proposed as being an intermediate in VSCs production by L. lactis.

Representativeness of extracts of offset paper packaging and analysis of the main odor-active compounds.

Packagings often carry odors due to the support and printing inks. The aim of the investigation was to define a representative solvent-free extract of paper-based packaging materials printed by the offset process, for the identification of the odor-causing volatile compounds. Static headspace and solid-phase microextraction were the two applied extraction methods. Representativeness tests showed that the odor of the PDMS fiber extract gave satisfying odor similarities with the original packaging. The sample incubation was performed at 40 degrees C for 30 min, whereas the extraction time was 3 min at 40 degrees C. Extracts of both the nonprinted and printed papers of different batches were analyzed by gas chromatography-olfactometry. 4-Phenylcyclohexene was identified as the most potent compound contributing to the latex-like odor of the nonprinted paper. Among the 13 major odorants identified by mass spectrometry, 10 were aldehydes and ketones generated by oxidation of the printing ink resins. The ratio of odorants to interferences was too low for a possible detection of the key odorants by nonseparative techniques such as sensor arrays.

Isolation and characterization of efficient isoxaben-transforming Microbacterium sp strains from four European soils.

Nutrient-agar plates containing isoxaben (500 mg litre(-1)) were used to isolate isoxaben-metabolising bacteria from four European soils incubated with the herbicide under laboratory conditions. In flask experiments, inoculation of a basal salts medium containing nitrogen and [phenyl-U-14C]isoxaben with an isolate (B2b) resulted in 33% recovery of the initial radioactivity as [14C]carbon dioxide after 2 weeks. A major metabolite identified by GC-MS and NMR analysis as 3-(1-ethyl-1-methylpropyl)isoxazol-5-ylamine accumulated both in basal salts and nutrient broth media. 2,6-Dimethoxybenzoic acid, a suspected metabolite of isoxaben, was not detected in either liquid media. However, the capability of the B2b isolate to use 2,6-dimethoxybenzoic acid as a source of carbon was demonstrated. Soil inoculation with the B2b strain resulted in an increase in the recovery of [14C] carbon dioxide from both [phenyl-U-14C] and [isoxazole-5-14C]isoxaben. The metabolite identified as 3-(1-ethyl-1-methylpropyl)isoxazole-5-ylamine only accumulated if the soil was autoclaved before inoculation. This metabolite was rapidly mineralized by the microflora of a natural soil without history of isoxaben treatment. Homology patterns of sequenced 16S rDNA between isoxaben-transforming isolates and reference strains showed that the four isolates identified belonged to the genus Microbacterium.

An atmospheric pressure chemical ionization-ion-trap mass spectrometer for the on-line analysis of volatile compounds in foods: a tool for linking aroma release to aroma perception.

An atmospheric pressure chemical ionization ion-trap mass spectrometer was set up for the on-line analysis of aroma compounds. This instrument, which has been successfully employed for some years in several in vitro and in vivo flavour release studies, is described for the first time in detail. The ion source was fashioned from polyether ether ketone and operated at ambient pressure and temperature making use of a discharge corona pin facing coaxially the capillary ion entrance of the ion-trap mass spectrometer. Linear dynamic ranges (LDR), limits of detection (LOD) and other analytical characteristics have been re-evaluated. LDRs and LODs have been found fully compatible with the concentrations of aroma compounds commonly found in foods. Thus, detection limits have been found in the low ppt range for common flavouring aroma compounds (for example 5.3 ppt (0.82 ppbV) for ethyl hexanoate and 4.8 ppt (1.0 ppbV) for 2,5-dimethylpyrazine). This makes the instrument applicable for in vitro and in vivo aroma release investigations. The use of dynamic sensory techniques such as the temporal dominance of sensations (TDS) method conducted simultaneously with in vivo aroma release measurements allowed to get some new insights in the link between flavour release and flavour perception.

Comparison of direct mass spectrometry methods for the on-line analysis of volatile compounds in foods.

For the on-line monitoring of flavour compound release, atmospheric pressure chemical ionization (APCI) and proton transfer reaction (PTR) combined to mass spectrometry (MS) are the most often used ionization technologies. APCI-MS was questioned for the quantification of volatiles in complex mixtures, but direct comparisons of APCI and PTR techniques applied on the same samples remain scarce. The aim of this work was to compare the potentialities of both techniques for the study of in vitro and in vivo flavour release. Aroma release from flavoured aqueous solutions (in vitro measurements in Teflon bags and glass vials) or flavoured candies (in vivo measurements on six panellists) was studied using APCI- and PTR-MS. Very similar results were obtained with both techniques. Their sensitivities, expressed as limit of detection of 2,5-dimethylpyrazine, were found equivalent at 12 ng/l air. Analyses of Teflon bag headspace revealed a poor repeatability and important ionization competitions with both APCI- and PTR-MS, particularly between an ester and a secondary alcohol. These phenomena were attributed to dependency on moisture content, gas/liquid volume ratio, proton affinities and product ion distribution, together with inherent drawbacks of Teflon bags (adsorption, condensation of water and polar molecules). Concerning the analyses of vial headspace and in vivo analyses, similar results were obtained with both techniques, revealing no competition phenomena. This study highlighted the equivalent performances of APCI-MS and PTR-MS for in vitro and in vivo flavour release investigations and provided useful data on the problematic use of sample bags for headspace analyses.

A detailed identification study on high-temperature degradation products of oleic and linoleic acid methyl esters by GC-MS and GC-FTIR.

GC-MS and GC-FTIR were complementarily applied to identify oxidation compounds formed under frying conditions in methyl oleate and linoleate heated at 180°C. The study was focused on the compounds that originated through hydroperoxide scission that remain attached to the glyceridic backbone in fats and oils and form part of non-volatile molecules. Twenty-one short-chain esterified compounds, consisting of 8 aldehydes, 3 methyl ketones, 4 primary alcohols, 5 alkanes and 1 furan, were identified. In addition, twenty non-esterified volatile compounds, consisting of alcohols, aldehydes and acids, were also identified as major non-esterified components. Furanoid compounds of 18 carbon atoms formed by a different route were also identified in this study. Overall, the composition of the small fraction originated from hydroperoxide scission provides a clear idea of the complexity of the new compounds formed during thermoxidation and frying.