Isabelle Souchon

Validation of a new in vitro dynamic system to simulate infant digestion.

Understanding the mechanisms of infant formula disintegration in the infant gastrointestinal tract is a key step for developing new formulas with health benefits for the neonate. For ethical reasons, the access to in vivo data obtained on infants is limited. The use of animal models can be an alternative but these experiments are labour intensive, expensive and results obtained show high inter-individual variability, making their interpretation difficult. The aim of this work was to develop a simple in vitro dynamic gastrointestinal digestion system, for studying infant formula digestion, and to validate it by comparing the kinetics of proteolysis obtained in vitro with in vivo data collected from piglets. Results showed a good correlation between in vitro and in vivo data and confirmed the rapid hydrolysis of caseins in gastric conditions, whereas whey proteins appeared more resistant to digestion.

Recovery of sulfur aroma compounds using membrane-based solvent extraction

Abstract This work focuses on a non-destructive process for recovering valuable aromatic fractions from the food industry’s odorous wastewaters. Non-dispersive solvent extraction of three sulfur aroma compounds, dimethyldisulfide, dimethyltrisulfide and S -methyl thiobutanoate, was carried out from very diluted aqueous solutions representing real effluent. The mass transfer from water to n -hexane was studied using a cross-flow designed hollow fiber membrane contactor. A preliminary study showed high affinity of solutes for n -hexane, with constant partition coefficients at infinite dilution between water and hexane in a 90–560 range. The influence of tube and shell side hydrodynamics on mass transfer was studied, with the aqueous phase on the tube side, and the organic phase on the shell side. The diffusion of solutes from the bulk aqueous phase to the aqueous–organic interface controlled the separation and contributed, under the conditions tested, to more than 97% of the overall mass transfer resistance. A resistance-in-series model overestimated overall mass transfer coefficients. The main explanation is the inaccuracy of the Leveque correlation used at low Reynolds numbers. The choice of a correlation for predicting mass transfers in the solvent phase did not affect the estimation, since the corresponding mass transfer resistance was negligible. Mass transfer fluxes obtained experimentally by membrane-based solvent extraction were greater for the three aroma compounds than those obtained by pervaporation.

Impact of Swallowing on the Dynamics of Aroma Release and Perception during the Consumption of Alcoholic Beverages

The consumption protocol used during alcoholic beverage tasting may affect aroma perception. We used an integrated approach combining sensory analysis and physicochemistry to investigate the impact of swallowing on aroma release and perception. A panel of 10 persons evaluated the dynamics of aroma perception during the consumption of a commercial flavored vodka, using the method of temporal dominance of sensations. Two protocols (spitting out or swallowing of the product) were tested. Nosespace analysis was simultaneously carried out by proton transfer reaction mass spectrometry to evaluate aroma release in the nasal cavity. Comparison of the results obtained with the 2 protocols highlighted significant differences in both the perception and the release of aroma: the swallowing of the product resulted in more complex perceptions but decreased the dominance rates of aromatic attributes. Ethanol perception also had an impact when the product was swallowed. Aroma release data partly accounted for the differences in perception, particularly as concerned ethanol release. The time at which dominance appears as well as the dominance duration of some attributes can be related to some temporal parameters of release data. But the lack of knowledge concerning the variety and complexity of mechanisms continues to limit our understanding of relationship between aroma release and perception.

Liquid-liquid extraction and air stripping in membrane contactor: application to aroma compounds recovery

This work focuses on a non-destructive process for recovering valuable aromatic fractions from odorous industry aqueous effluent. Non-dispersive extraction often selected aroma compound was carried out on very diluted model aqueous solutions, using membrane contactors, in two configurations: liquid-liquid and liquid-gas. Mass transfers from water to n-hexane, from water to miglyol (two solvents widely used in aromatic industry) and from water to air were studied using a cross-flow designed hollow fibre membrane contactor. The influence of physico-chemical properties of the aroma compounds and the influence of the solvent viscosity on mass transfer are discussed. Moreover, a resistance-in-series model has been applied and allowed to predict the mass transfer intensity in agreement with experimental values whatever the separation principle, liquid-liquid or liquid-gas.

Pervaporation as a deodorization process applied to food industry effluents: recovery and valorisation of aroma compounds from cauliflower blanching water

Abstract In the food industry, unit operations of stabilisation (such as blanching) produce aqueous effluents generally non-polluting but often odorous. The objective of this study was to apply the pervaporation process to the deodorization of a cauliflower blanching effluent in order to reduce its volatile organic compounds content and to try to recover a valuable food flavouring fraction. A systematic study of pervaporation has been performed on three sulfur compounds identified as typical compounds of the cauliflower odour. Then, the separation performances obtained on an industrial effluent were evaluated through physico-chemical and sensorial analysis. They showed that pervaporation was an efficient process for deodorization and offers a real potential for valorisation of the permeate.

A biomechanical model of swallowing for understanding the influence of saliva and food bolus viscosity on flavor release.

After swallowing a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The objective of the present article was to understand and quantify physical mechanisms explaining pharyngeal mucosa coating. An elastohydrodynamic model of swallowing was developed for Newtonian liquids that focused on the most occluded region of the pharyngeal peristaltic wave. The model took lubrication by saliva film and mucosa deformability into account. Food bolus flow rate and generated load were predicted as functions of three dimensionless variables: the dimensionless saliva flow rate, the viscosity ratio between saliva and the food bolus, and the elasticity number. Considering physiological conditions, the results were applied to predict aroma release kinetics. Two sets of conditions were distinguished. The first one was obtained when the saliva film is thin, in which case food bolus viscosity has a strong impact on mucosa coating and on flavor release. More importantly, we demonstrated the existence of a second set of conditions. It was obtained when the saliva film is thick and the food bolus coating the mucosa is very diluted by saliva during the swallowing process and the impact of its viscosity on flavor release is weak. This last phenomenon explains physically in vivo observations for Newtonian food products found in the literature. Moreover, in this case, the predicted thickness of the mix of food bolus with saliva coating the mucosa is approximately of 20 μm; value in agreement with orders of magnitude found in the literature.

Recovery of aroma compounds from tomato industry effluent using membrane-based solvent extraction☆

This work focuses on a non-destructive process for recovering valuable aromatic fractions from an odorous tomato industry aqueous effluent. Non-dispersive solvent extraction of four selected aroma compounds, chosen as key aroma, was, at first, carried out on very diluted model aqueous solutions. Mass transfers from water to n-hexane and from water to Miglyol (two solvents widely used in aromatic industry) were studied using a cross-flow designed hollow fibre membrane contactor. The influence of physico-chemical properties of the aroma compounds studied and the influence of the solvent viscosity on mass transfer are discussed. The results obtained with model solutions have been validated on the industrial process effluent.

Main individual and product characteristics influencing in-mouth flavour release during eating masticated food products with different textures: mechanistic modelling and experimental validation.

A mechanistic model predicting flavour release during oral processing of masticated foods was developed. The description of main physiological steps (product mastication and swallowing) and physical mechanisms (mass transfer, product breakdown and dissolution) occurring while eating allowed satisfactory simulation of in vivo release profiles of ethyl propanoate and 2-nonanone, measured by Atmospheric Pressure Chemical Ionization Mass Spectrometry on ten representative subjects during the consumption of four cheeses with different textures. Model sensitivity analysis showed that the main parameters affecting release intensity were the product dissolution rate in the mouth, the mass transfer coefficient in the bolus, the air-bolus contact area in the mouth and the respiratory frequency. Parameters furthermore affecting release dynamics were the mastication phase duration, the velopharynx opening and the rate of saliva incorporation into the bolus. Specific retention of 2-nonanone on mucosa was assumed to explain aroma release kinetics and confirmed when gaseous samples were consumed.

A lubrication analysis of pharyngeal peristalsis: application to flavour release.

After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The aim of this article was to analyse the fluid mechanics of pharyngeal peristalsis and to develop a simple biomechanical model in order to understand the role of saliva and food bolus viscosity on the coating of pharyngeal mucosa. We began by analysing the physiology and the biomechanics of swallowing in order to determine relevant model assumptions. This analysis of the literature clarified the types of mechanical solicitations applied on the food bolus. Moreover, we showed that the pharyngeal peristalsis in the most occluded region is equivalent to a forward roll coating process, the originality of which is lubrication by a film of saliva. A model based on the lubrication theory for Newtonian liquids was developed in dimensionless form. The parametric study showed the strong influence of relative saliva thickness on the food bolus coating. A specific experimental device was designed that confirms the model predictions. Two sets of conditions that depend on the relative thickness of saliva were distinguished. The first is characterised by a relatively thin film of saliva: food bolus viscosity has a strong impact on mucosa coating. These phenomena are well represented by the model developed here. The second is obtained when the saliva film is relatively thick: hydrodynamic mixing with saliva, interdiffusion or instabilities may govern mucosa coating. Finally, these results were extrapolated to determine the influence of food bolus viscosity on the dynamic profile of flavour release according to physiological parameters.

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 12u2009ng/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.