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.
Thermodynamic parameters (T, ΔH°, ΔS°, 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 ΔH° and ΔS° 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.
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. Copyright
Diffusion properties at macroscopic and microscopic scales for three aroma compounds (in solution and gel systems) were characterized using three different methodologies: the diffusion cell and the ...Volatile Air Stripping Kinetic methods for the determination of apparent diffusion coefficients and the pulsed-field-gradient Nuclear Magnetic Resonance method for the determination of self-diffusion coefficients. The accuracy of the methods was established by comparing ethyl hexanoate diffusion coefficient in water or D
2O solution and in 1%-agar gel system at 25 and 30
°C. The robustness of the three methodologies was also investigated in 1%-
iota-carrageenan system with different NaCl content leading to gel strengthening.
In 1%-agar gel as well as in 1%-
iota-carrageenan systems, the apparent or self-diffusion coefficients of aroma compounds had the same order of magnitude regardless of the approach, ranging between 2.3
×
10
−10 and 10.4
×
10
−10
m
2
s
−1. Diffusion properties were discussed in terms of the different observation scales (diffusion scales) and of the nature of gel network.
► Largely used PRV method suffers for several biases already pointed. ► We propose a second-order equation PRV model. ► Pseudo-chromatographic data were generated to test this PRV second-order. ► PRV ...second-order model allows to obtain the more realistic pseudo-data. ► PRV second-order model reduces the risk of biased partition coefficient determination.
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 (PRV1) and the proposed, second-order model (PRV2). Thus, pseudo-data obtained from simulations were compared to published experimental data. We observed that the second-order model, PRV2, produces a lower variability, allowing improved K precision. Moreover, the obtained K(PRV2) values are very close to those obtained by classical equilibrium headspace analysis (EHSA). The PRV2 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.
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 ι-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 ι-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. Keywords: ι-Carrageenan; gels; aroma release; partition coefficient; interaction; headspace analysis; QSAR; QSPR; genetic function approximation
Interaction of flavor compounds with proteins is known to have an influence on the release of flavor from food. Hydrophobic interactions were found between β-lactoglobulin and methyl ketones; the ...affinity constant increases by increasing the hydrophobic chain. Addition of β-lactoglobulin (0.5 and 1%) to aroma solutions (12.5, 50, and 100 μL L-1) of three methyl ketones induces a significant decrease in odor intensity. The chosen methyl ketones were 2-heptanone (K b = 330), 2-octanone (K b = 950), and 2-nonanone (K b = 2440). The release of these flavor compounds (50 μL L-1) was studied by static headspace in water solution (50 mM NaCl, pH 3) with different concentrations of β-lactoglobulin (0, 0.5, 1, 2, 3, and 4%). Increasing the concentration of protein increases the retention of volatiles, and this effect is greatest for 2-nonanone, the compound with the highest affinity constant, and lowest for 2-heptanone. A mathematical model previously developed to describe flavor release from aqueous solutions containing flavor-binding polymers (Harrison, M.; Hills, B. P. J. Agric. Food Chem. 1997, 45, 1883−1890) was used to interpret the data. The model assumes that the polymer−flavor interaction is reversible and the rate-limiting step for release is the transfer of volatiles across the macroscopic gas−liquid interface. This model was used to predict the equilibrium partitioning properties and the rate of release of the three methyl ketones. Increasing the affinity constant leads to decreased release rates and a lower final headspace aroma concentration. Keywords: Binding; aroma; protein; odor intensity; mathematical modeling; interfacial mass transfer; partitioning
The objective of this work was to study the putative interactions between flavour compounds and coffee melanoidins. After extraction,melanoidins were freeze-dried and several flavour compounds from ...different chemical classes were tested in aqueous solution. The retention of flavour compounds by melanoidins was found to be different in function of the method or time of freezedrying. Thus,for the same freeze-drying method,the retention capacity of melanoidins increased when the aliphatic chain length of a homologous series of flavour compounds increased. This observation seems to favour the hydrophobic nature of the interactions between melanoidins and flavour molecules. Moreover,for the same aroma compound,the retention capacity of coffee melanoidins was found to vary in function of the freeze-drying method used. Freeze-drying could therefore be involved in the modification of the surface properties of melanoidins or in their denaturation,modifying their retention ability towards volatile flavour compounds. At last,retention by coffee melanoidanins decreased with the roasting degree of coffee.
The aims of this study were (1) to study the effect of lyophilized coffee extract on the retention of aroma compounds and (2) to study if aroma compounds selected are differently affected by the ...lyophilized coffee extracts obtained from conventional and Torrefacto coffee brews prepared by filter coffeemaker and by espresso coffee machine. Variable amounts of lyophilized coffee extracts, relative to coffee powder, containing different percentages of high molecular weight compounds, mainly melanoidins (value given in parentheses), were obtained: 20.9% (14.8) and 24.9% (23.3), respectively, for conventional and Torrefacto coffee brew prepared by filter coffeemaker and 18.1% (18.8) and 20.7% (57.5), respectively, for conventional and Torrefacto coffee brew prepared by espresso coffee machine. The retention of aroma compounds increased by increasing the lyophilized coffee extract concentration and was found to be dependent on the aroma compounds. The retention of aroma compounds was found to be slightly different depending on the brewing procedure employed, showing lyophilized coffee extracts obtained with espresso coffee machine had higher retention values that those extracted by filter coffeemaker. Retention capacity of lyophilized coffee extracts obtained from the conventional and the Torrefacto roasted coffee did not show differences except in the case of ethyl nonanoate.
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.
PDF
