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Acid milk gels with fat (3.5 or 10%) or without fat containing 0.2–1% of whey proteins (WP) or 0.2–1.5% of protein aggregates (fractal aggregates, microgels and mixed casein/WP aggregates with an 80/20 ratio) were investigated. The fat-containing systems were homogenized and the systems were preheated (90 °C, 11 min) and acidified to a pH of 4.6 by adding glucono-delta-lactone. The protein composition of the fat droplet interface was characterized by SDS-PAGE and the textural and rheological properties, microstructure, and whey separation of acid networks were determined. WP and fractal aggregates showed the best ability to improve the textural properties and microstructure of all acid milk gels and reduce whey separation. Increasing the concentrations in microgels and mixed aggregates did not lead to an increase in gel firmness or generate a strong impact on the protein network, but a high concentration in mixed aggregates could reduce whey separation. The fat droplet interface was made almost exclusively of caseins, even if the fractal aggregates could also be adsorbed when the interfacial surface was increased either through fat content or through an increase in homogenization pressure. Adding proteins changes the textural properties of the acid gels in all the systems, mainly due to their role in the continuous phase.

International audience; The effect of pea protein fortification on the rheological properties of sponge-cake batters and their continuous phases, as well as their relationship with the final product properties were studied. Foams made out of whole egg and sugar were prepared in a planetary mixer; wheat flour (WF) was added to form a typical sponge-cake batter. Pea protein isolates (PP) were added in substitution to WF to form five batters with various PP concentrations expressed as the percentage of WF substitution: 0, 10, 20, 30 and 40%. The batter air volume fraction decreased when increasing PP concentration, which led to an increase in the cake density and apparent Young modulus. All batters and their respective continuous liquid phases showed shear-thinning behavior, which was modeled by a power law. They showed a predominant elastic behavior at intermediate frequencies, and a cross-over point at high frequencies. All of the rheological properties increased by a factor of about 10 when the PP concentration increased from 0 to 40%. Free-drainage experiments showed that batter stability increased with increasing PP concentration. PP had larger particles than WF, and showed a higher water binding capacity than WF, but no significant difference in solubility. Observations of the batter and cake microstructure revealed PP formed a network of interconnected "bridged" particles in the continuous phase. These results suggest that PP first acted as fillers that swelled and connected to each other in the continuous phase, and were the main driver for the increase of rheological properties.

Sugar beet pectin is a byproduct of the sugar industry with a particularly low gelling power which hinders its application as gelling agent and thickener. Here we consider the use of freeze casting to shape sugar beet pectin into lightweight foams. Freeze casting processing conditions such as the applied thermal gradient and the polysaccharide concentration were explored to obtain macroporous lightweight foams with different textures. The precise control over the foams texture and pore anisotropy was decisive for their performance as liquid transport devices by capillary ascension and for their mechanical performance. Overall, the obtained results show that the formation of highly anisotropic structures using freeze casting can be instrumental in the upcycling of polysaccharide industrial byproducts., Comment: 24 pages, 7 figures

International audience; Polysaccharide-surfactant blends are widely used in foods. However, their possible mutual interactions have not been extensively studied. The purpose of this work was to examine how the anionic surfactant sodium stearoyl lactylate (SSL) affects different properties of κ-carrageenan solutions and gels. Rheometry, differential scanning calorimetry, asymmetrical flow field-flow fractionation coupled with multiangle laser light scattering, among others, were used to determine the flow and viscoelastic behavior, thermal transitions, and conformation changes, respectively. Interference caused by SSL is postulated as the primary factor to explain the variations in the conformation of κ-carrageenan in gels and solutions. However, electrostatic repulsions between κ-carrageenan and SSL can also be involved. These latter interactions are more important for high SSL concentrations (13 mmol dm−3) without addition of KCl, because of the higher net negative charge density of the system. SSL significantly modifies the properties of κ-carrageenan in aqueous media.

A gene encoding a novel dextransucrase was identified in the genome of Oenococcus kitaharae DSM17330 and cloned into E. coli . With a kcat of 691 s −1 and a half-life time of 111 h at 30 °C, the resulting recombinant enzyme -named DSR-OK- stands as one of the most efficient and stable dextransucrase characterized to date. From sucrose, this enzyme catalyzes the synthesis of a quasi linear dextran with a molar mass higher than 1 × 10 9 g·mol −1 that presents uncommon rheological properties such as a higher viscosity than that of the most industrially used dextran from L. mesenteroides NRRL-B-512F, a yield stress that was never described before for any type of dextran, as well as a gel-like structure. All these properties open the way to a vast array of new applications in health, food/feed, bulk or fine chemicals fields.

During heat treatment, whey proteins (WP) are denatured and form different kinds of whey protein aggregates (WPA) depending on the physico-chemical conditions. In the presence of casein micelles, mixed aggregates (MA), resulting from the interaction of κ-casein and WP, are formed. The aim of this study is to understand the effect of pH on the WPA structure and the impact of the casein/whey proteins (Cas/WP) ratio on MA morphology. In this work, WP solutions were heated at pH 5.8 or 7 to produce WPA. On the other hand, aqueous mixtures containing three Cas/WP ratios (82/18, 56/44 and 30/70) were heated at 80 °C during 1 h at pH 6.3 to obtain MA. Milk protein aggregates were analyzed by Transmission Electron Microscopy (TEM) and Asymmetrical Flow Field-Flow Fractionation coupled with Multiangle Laser Light Scattering and Differential Refractometer (AF4-MALLS-DRi). Dense and spherical WPA were formed at pH 5.8 whereas branched and fractal aggregates were obtained at pH 7. Regarding MA, results suggested that they were mainly produced with the 82/18 Cas/WP ratio whereas a majority of WPA was obtained with the 30/70 ratio. At intermediate ratio, the mixture was composed of small MA and WPA that did not interact with κ-casein. Moreover, WP seem to interact preferentially with larger casein micelles. Thereby, AF4-MALLS-DRi proved to be a powerfull technique to characterize the complex structure of milk protein aggregates and an interesting alternative to size exclusion chromatography especially for MA and casein micelles which interact with the stationary phase and are retained in the column.

National audience

International audience; The effects of konjac glucomannan (KGM) on the gelatinization, retrogradation and complexation properties of potato and broad bean starches were investigated by differential scanning calorimetry and X ray diffraction. It was established that the addition of 1% KGM in starch suspensions causes a slight decrease in the amount of available water in the system. However, this seems sufficient to disrupt the gelatinization and the retrogradation of potato and broad bean starches. In addition, the ability of amylose to interact with carvacrol is strongly affected by the presence of KGM. A rheology study showed on one hand that addition of KGM to starch decreased the gel character of the system, irrespective of the presence of carvacrol. However, carvacrol induced a strong increase of the storage modulus of starch gel for the same KGM content.

International audience; Pectins are complex branched polysaccharides present in primary cell walls. As a distinctive feature, they contain high amount of partly methyl-esterified galacturonic acid and low amount of rhamnose and carry arabinose and galactose as major neutral sugars. Due to their structural complexity, they are modifiable by many different enzymes, including hydrolases, lyases, and esterases. Their peculiar structure is the origin of their physicochemical properties. Among others, their remarkable gelling properties make them a key additive for food industries. Pectin-degrading enzymes and -modifying enzymes may be used in a wide variety of applications to modulate pectin properties or produce pectin derivatives and oligosaccharides with functional as well as nutritional interests. This paper reviews the scientific information available on pectin structure, pectin-modifying enzymes, and the use of enzymes to produce pectin with controlled structure or pectin-derived oligosaccharides, with functional or nutritional interesting properties.

Le but principal de cette etude est d’examiner les representations de la depression a travers trois enjeux sociaux entourant son traitement : 1-la hausse des consultations relatives a la depression, 2-la hausse des prescriptions d’antidepresseurs et 3-les difficultes d’adhesion aux traitements antidepresseurs. Ces representations sociales ont ete etudiees a l’aide d’un questionnaire proposant des raisons pour expliquer la presence de ces trois phenomenes. Les participants sont 43 patients depressifs, 92 professionnels de la sante mentale (omnipraticiens, psychiatres, psychologues) et 350 etudiants universitaires provenant du Quebec. Les resultats font emerger des representations consensuelles a travers les groupes ainsi que des positionnements distinctifs en fonction des enjeux particuliers. Les resultats sont globalement coherents avec l’orientation des principes organisateurs, la theorie de l’implication et la fonction identitaire des representations sociales.

International audience

International audience; Pectins account for one of the major polysaccharides of plant cell walls and are commonly used in the food industry as gelling and stabilising agents. Pectin methylesterase (PME) can alter pectin structure and affect their gelling properties by de-esterifying galacturonic acid. Previously, we reported different behaviours of plant and fungal PMEs on high methylated pectins in solution or during the gelling process (Slavov et al., 2009). In the present study, the behaviour of the two PMEs is studied on a medium methylated pectin in solution, i.e. in the absence of calcium, or during the gelling process, i.e. in the presence of calcium. Only slight modifications were observed for Aspergillus aculeatus PME behaviour between the two conditions. On the opposite we show a role of calcium on the processivity of orange PME: the processivity decreases in the presence of calcium. (C) 2011 Elsevier Ltd. All rights reserved.

Le silence qui recouvre les abus sexuels incestueux, souvent subis a un âge prepubere, constitue une entrave dans la construction de l’identite, de la relation de couple et de la filiation. L’article s’appuie sur trois vignettes cliniques pour illustrer ce constat et montre que la lente reconstruction apres ces traumatismes est le fait d’une parole tenue dans un cadre analytique ou l’interdit du toucher et l’absence d’emprise sont la regle.

International audience; Rheology, micro-DSC and confocal microscopy were used to study the effect of potassium ion on the viscoelastic behavior, disorder-order transition and microstructure, respectively, of kappa-carrageenan in solution under different conformations at 60, 25 and 9 degrees C. At 60 and 25 degrees C the rheological behavior of 0.5% kappa-carrageenan with 0-80 mmol/dm(3) and 0-5 mmol/dm(3) KCl, respectively, was typical of viscoelastic solutions of random coiled polymers. At 9 degrees C and below a critical ionic concentration of about 7.0 mmol/dm(3), kappa-carrageenan adopted an ordered conformation in which helical structures did not aggregate and hence did not form self-supporting gels. Changes in polysaccharide stiffness were estimated from intrinsic viscosity variations as a function of ionic content. In the ordered state, the stiffness was higher than in the disordered state, whereas a liquid-like viscoelastic behavior was still exhibited. In 0.5% kappa-carrageenan at 25 degrees C, increasing KCl from 0 to 300 mmol/dm(3) produced gels of increasing rigidity. However, above 100 mmol/dm(3) such increase was marginal. Confocal images evidenced a three-dimensional network whose continuity depends on polysaccharide and salt concentrations. These observations are consistent with the rheological behavior of the self-supporting gels obtained with kappa-carrageenan concentrations in the range of 0.05-1%

International audience; This work aims to investigate the theological properties of microfibrillated cellulose (MFC) suspensions. The effect of some experimental parameters, such as cellulose concentration, temperature, ionic strength and pH has been studied. For that purpose, suspensions of microfibrillated cellulose have been prepared by strong mechanical treatments of a purified sugar-beet pulp cellulose-based residue in aqueous medium. Cellulose suspensions at different concentrations (from 0.25 to 3 w/w%.) have been found to display a viscoelastic solid-like behaviour, even for the lowest concentration tested. The storage modulus at 0.1 rad s(-1) increased strongly upon increasing concentration from 0.25 to 3 w/w%, following a power law with an exponent of 2.58. All suspensions exhibited a shear-thinning behaviour. It was also found that viscoelastic properties of the suspensions of cellulose are not affected by temperature or by varying pH from 4.5 to 9 while the G' and G '' moduli increased as salt concentration of the suspensions increased. This reinforcement of the viscoelastic properties by increasing ionic strength can be related to a screening of the electrostatic repulsions between the microfibrils, due to the presence of uronic acid groups, enhancing the fiber-fiber interactions. Mechanical treatment did not affect cellulose crystallinity. The effect of freezing was investigated as an alternative way to the most conventional cellulose preparation that consists to freeze-dry the suspensions for their conservation. It was shown that freezing preserved the rheological properties of the suspensions, contrary to freeze drying

International audience; High methoxy pectin was submitted to various amounts of a fungal pectin methylesterase (PME) from Aspergillus aculeatus and of a plant PME from orange in the presence of calcium. The systems were characterized by rheological means during the gelation process. By the way of in situ demethoxylation with low amount of orange PME, it was possible to gel pectin from the beginning of the reaction although its high degree of methylation around 70. To understand this unusual properties, the behaviour of the two enzymes was investigated in pectic gels and in solution through the analysis of content and distribution of the remaining methyl esters. In the gel, the degree of methylation decreased slowly with orange PME and rapidly with Aspergillus PME. The degree of methylation and degree of blockiness after treatment with each PME in solution or in gels were slightly different. Possible explanations for this are evolving visco-elastic properties, including gel formation or influence of calcium on the enzyme–substrate complex.

L’alimentation est devenue une préoccupation importante des sociétés occidentales en raison de ses conséquences sur la santé et le développement de l’enfant. Le présent article fera état, à partir du cadre théorique des représentations sociales, des résultats d’une classification descendante hiérarchique et d’une analyse factorielle du champ représentationnel lié à l’alimentation, la santé et la maladie des jeunes enfants (90 : maternelle et première année). On y retrouvera les principales dimensions qui organisent le champ de signification des représentations sociales et leur positionnement selon diverses variables socio-économiques. L’articulation équivoque des représentations sociales de l’alimentation, de la santé et de la maladie, en témoignant des interférences qui agissent dans l’environnement social des jeunes enfants, prêche en faveur des interventions en service social portant sur les aspects socioculturels de l’alimentation., Dysfunctional feeding has become an important preoccupation of occidental societies due to the consequences on the health and development of the child. The present article will present, within a theoretical context of social representations, results of a descending hierarchical classification and of a factorial analysis of a graphical field of nutrition linked to health and sickness of young children (90: kindergarten and first grade). We will find the principal dimensions that organize the signification of the field of social representation and their position according to the diverse socioeconomic variables. Equivocal articulation of social representation of alimentation, health and disease testifies of the interferences that play’s a role in social environment of young children and that goes on in favour of social service intervention of alimentation sociocultural aspects.

The modulation of the reinforcement effect brought by the addition of tunicate cellulose nanowhiskers with different surface charge densities to an agarose hydrogel matrix has been studied using linear viscoelastic measurements. The cellulose nanowhiskers were characterized using transmission electron microscopy, and their surface charge was determined by a titration method. The results show that increasing the charge at the surface of nanowhiskers tends to enhance the reinforcement effect, because of a better dispersion of nanowhiskers. However, the results also suggest the existence of an optimum surface charge, corresponding to a maximum reinforcement effect at a given volume fraction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43063.

De nombreux travaux ethnologiques et psychologiques ont porté sur les répercussions des usages de drogues et, plus récemment, des médicaments sur les fonctions sexuelles. Nous présentons dans cet article les principales dimensions dégagées sur cette question. Dans un premier temps, les substances aphrodisiaques principales sont envisagées à partir des perspectives ethnologiques et expérimentales. Cette recension montre la diversité des contextes et des produits employés, de même que la variabilité des effets. La seconde section porte sur les drogues de synthèse contemporaines, à leurs contextes d’utilisation ainsi qu’aux conséquences sur la sexualité et la prise de risques face aux infections transmissibles sexuellement (ITS) et au VIH/sida. La troisième partie porte sur les développements pharmacologiques qui modulent la fonction sexuelle de même que sur les usages détournés des médicaments à des fins sexuelles récréatives. Ce survol des recherches contemporaines met en évidence la place importante de l’érotisme dans la consommation des différentes substances et l’intérêt de développer un programme d’études plus précis dans ce domaine.

Changes in the mechanical and micro-structural properties of cake batter as a function of formulation impact are described. Mechanical properties were investigated by batter rheology and cake texture. Confocal laser scanning microscope (CLSM), together with image analysis technique, was used to obtain the microstructure of batters and cakes. Results showed an increase in rheological moduli values with the addition of pregelatinized starch in the batter, while fat replacement by rapeseed oil decreased the moduli values of the batter. These changes in batter visco-elastic properties resulted in different cake structures. A significant increase in the surface area of the lipid domain has been observed on CLSM images for cakes using pregelatinized starches. This was explained by the fact that part or all of the pregelatinized starch was embedded in the lipid domain for these formulations. This fact may explain the expected softer texture of the cake using such starches. CLSM in combination with image processing has been proved as an applicable tool for examining and quantifying the fat and protein microstructure in batter and cake. Hence, it was possible to prove the dependency of the texture on the microstructure of the batter and the baked “cake”.

International audience; Dynamic oscillatory shear and confocal laser scanning microscopy were used, respectively, to study the viscoelastic properties and ultrastructure of mixtures of unmodified waxy maize starch (3%) and gellan (0.005–0.05%), pasted at 75 and 90 °C. The two temperatures resulted in different rheological properties and ultrastructure. At 75 °C swollen and partially disrupted granules were observed, while at 90 °C the dominant feature was the presence of granule remnants. Addition of gellan produced mixtures with different elastic properties depending on the extent of granular disruption and gellan concentration in the mixture. Below 0.02% gellan, swollen and disrupted starch granules were surrounded by compact, yet slightly interconnected, gellan networks resulting in enhanced blends at both temperatures. Above such gellan concentration no enhancement was observed and gellan dominated the viscoelastic behavior of the mixtures because of the existence of more evenly distributed networks with swollen or disrupted starch granules exerting a weakening effect on the resulting structure.

Resume: L'enseignement des sciences et des techniques fait l'objet de preoccupations en raison de leur importance dans la formation des eleves du secondaire et de l'impact qu'elles ont sur leur orientation scolaire et socioprofessionnelle future. Les conceptions que les educateurs entretiennent au regard des disciplines scientifiques et les pratiques qu'ils exercent influencent pour une bonne part celles des eleves ainsi que les apprentissages qu'ils font. Le present article, qui s'inscrit dans le cadre d'une etude d'ensemble sur les representations sociales des sciences et des technologies chez les differents acteurs educatifs et chez les eleves du secondaire, fait etat des postures specifiques endossees par des enseignants de sciences en lien avec un tel enseignement et tente, sur la base des discours qu'ils produisent, d'en degager les significations, les preoccupations sociales invoquees et le caractere mediateur de l'activite didactico‐pedagogique engagee nous interessant particulierement.

The present investigation aimed at understanding how the type of cations (Na + and/or Ca 2+ ) influences heat-induced gelation of globular protein/LM pectin mixtures in comparison to the globular protein only. Two globular proteins (β-lactoglobulin or bovine serum albumin) were compared. On the basis of viscoelastic and microscopic observations (CLSM), it has been shown that the two cations play a major role in gelation of the individual biopolymers and, therefore, influence strongly the properties of the mixture. These differences are related to a competition between gelation of the protein (in absence of Ca 2+ ) or of both biopolymers (if Ca 2+ is added) and phase separation processes taking place before the mixed system is entirely gelled.

Cette etude empirique basee sur 110 entrevues menees aupres d’entreprises de biotechnologie propose une reflexion sur le couple creation de savoir/logique de gouvernance dans les firmes de haute technologie. Elle aboutit a la caracterisation de trois modes de developpement « pre-entrepreneurial », « entrepreneurial » et « managerial » dans les entreprises de biotechnologie dont l’evolution serait potentiellement marquee par deux ruptures: une rupture teleologique et un defi de creativite.

International audience; The dynamic rheology and confocal laser scanning microscopy (CLSM) of gellan at low concentrations (0.005–0.05 wt%) in the presence of 10 mM CaCl2 were investigated at 25 °C. DSC thermograms showed a conformational transition from coil to rigid helix at approximately 41 °C. Microscopy observations demonstrated that at these low gellan concentrations, the level of counter ions induced formation of a network, the compactness of which depended on gellan concentration. The reinforcement of the network structures by the increase of gellan concentration resulted in more elastic gels well evidenced through the rheology of the systems.

International audience; The influence of the addition of tunicate cellulose nanowhiskers on the structural and rheological properties of an agarose hydrogel matrix has been studied, with the objective to design innovative green material, with good mechanical properties. The cellulose nanowhiskers were characterized using transmission electron microscopy, and their charge surface density was determined by a titration method. Oscillatory shear and stress relaxation tests were performed in order to characterize the rheological properties of the agarose matrix, and of the agarose hydrogels filled by nanowhiskers at volume fractions below 0.2%. The results show a significant reinforcement effect due to the addition of nanowhiskers, and suggest changes in the matrix network structure induced by the cellulose nanoparticles.

The phase diagram of the guar–dextran aqueous two-phase system has been described on the basis of static light scattering measurements in the dilute regime. By determining the molar weight and second virial coefficient from the two single polymers and the second virial cross coefficient from mixtures at constant guar/dextran ratio (either 17/83 or 28/72), the thermodynamic models based on the virial expansion or the Flory–Huggins theory were successfully applied. The second virial coefficient of guar was difficult to estimate with enough accuracy by light scattering and therefore was obtained by adjustment using a simple criterion stating that the calculated spinodal passes through the experimental critical point. The obtained value was within the confidence interval given by light scattering. Virial expansion and Flory–Huggins approaches yielded quite similar theoretical phase diagrams that satisfactorily fitted the experimental one. The slight discrepancies observed on the position of binodals and critical points has been attributed to the polydispersity of guar or the difficulty in extrapolating from the dilute regime to the semidilute one. The slope of the tie-lines was predicted with a good accuracy, especially with the virial expansion model. The fact that both approaches gave such similar results is probably related to the fact that the expressions of chemical potentials are equivalent if the polymer concentrations are low enough. In this particular case, both models are based on excluded volume interactions and equally describe the phase behavior of the guar–dextran aqueous system.

The gelling properties of a 0.46 wt % semi-dilute aqueous suspension of well-characterized nanocrystalline cellulose particles extracted from the tunic of marine animals were studied by measuring the time evolution of linear viscoelastic moduli at various frequencies. The results show the existence of a gel time characterized by a frequency-independent loss angle, which suggests that gelling is due to the growth of self-similar clusters, whose fractal dimension was determined. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40676.

The partition of proteins (bovine serum albumin, β-lactoglobulin, micellar casein) has been examined in the guar/dextran aqueous two-phase system. The influence of parameters like pH, ionic strength (NaCl), and polymer concentration has been investigated while the protein concentration was increased up to 2% w/w. For globular proteins (bovine serum albumin, β-lactoglobulin) the general trends of partitioning established in the literature with other systems like polyethyleneoxide/dextran were nearly verified. The dextran-rich bottom phase was found to be slightly more concentrated in protein than the guar-enriched top one. However, micellar casein displayed a different behavior, giving a more uneven partition and phase separation phenomena at concentrations above 0.5% w/w. This difference has been attributed to the larger size of the particle. Meanwhile, the modifications of the guar/dextran phase diagram have been investigated. It was shown that the addition of globular protein or micellar casein up to 2% w/w did not affect the thermodynamic features of this system.

Can the theory of social representations contribute to the study of education relating to environment ? Four sets of themes are explored to show which conditions enable to realise the analysis of this particular field of education, with the help of the theory. Thus there should be tackled the diversity of viewpoints occurring in social debates, the constitution of groups or social rooting, the relationship between various forms of knowedge in an interdisciplinary perspective, and lastly the relationship between social representations and practices. The analysis of these conditions enables to conclude that the contribution of the theory of social representations for education relating to environment is definite, provided one goes beyond mere descriptive studies., La théorie des représentations sociales peut-elle contribuer à l'étude de l'éducation relative à l'environnement ? Quatre thématiques sont explorées pour montrer quelles sont les conditions qui permettent de réaliser l'analyse de ce champ particulier de l'éducation à l’aide de la théorie. Seraient ainsi abordées la diversité des points de vue qui prennent place dans les débats sociaux, la constitution des groupes ou ancrage social, le rapport entre les différents savoirs dans une perspective interdisciplinaire et, finalement, les rapports qu'entretiennent représentations et pratiques sociales. L'analyse de ces conditions permet de conclure que la contribution de la théorie des représentations sociales pour l'éducation relative à l'environnement est certaine à condition de dépasser les simples études descriptives., Garnier Catherine. Contribution de la théorie des représentations sociales au champ de l'éducation relative à l'environnement. In: Les dossiers des sciences de l'éducation, N°4, 2000. Représentations et engagements: des repères pour l’action. pp. 23-41.

The phase behaviour of micellar-casein (MC)–κ-carrageenan mixtures was investigated using different ionic forms of the carrageenan (Na + , K + ) in different ionic conditions and at two temperatures. At 50°C, that is above the conformational transition temperature of the carrageenan, a macroscopic phase separation was clearly evidenced. Accordingly, ternary phase diagrams were established as a function of the biopolymer concentration for each system. By analogy with other particulate systems, it was assumed that this phase separation originated from a depletion–flocculation mechanism. The ultrastructure of the MC–carrageenan mixtures is described at 20°C using confocal laser scanning microscopy and phase contrast microscopy. All observations showed that phase separation has taken place. A casein-rich phase was dispersed in a carrageenan-rich phase at a low casein content (below 3%); above this casein concentration in the mixtures, the phase separation process yielded a casein continuous network within the carrageenan network. It was suggested that the phase separation process initiated at 50°C was almost immediately inhibited by gelation upon cooling, resulting in a biphasic system the structure of which depended upon the initial composition.

The properties of micellar casein-galactomannan (guar gum and locust bean gum) mixed systems have been investigated at 20°C, pH 7 and in 0.25 m NaCl; in these conditions, the mixtures tended to phase separate probably due to depletion–flocculation mechanisms. The ternary phase diagram has been established for each galactomannan–casein system according to the biopolymer concentrations. The rheological properties of these mixed systems have been investigated in the monophasic domain, as well as in the biphasic one. Modifications of the flow and the viscoelastic properties were clearly evidenced in the two-phase domain. The ultrastructure of the galactomannan–micellar casein mixtures has been described using confocal laser scanning microscopy. In the biphasic domain, observations of the mixed system at concentrations corresponding to those of rheological measurements clearly evidenced that the phase separation process has yielded a continuous network mostly composed of the aggregated micellar casein.

The solution behavior of pectin polysaccharides has been investigated by small angle neutron scattering (SANS), viscosimetric, and molecular modeling studies. The samples used in the experimental study were obtained from apple and citrus and had degrees of methylation ranging from 28 to 73%, with a rhamnose content lying between 0.6 and 2.2%. Persistence lengths, derived from intrinsic viscosity measurements, ranged from 59 to 126 A, whereas those derived by SANS were between 45 and 75 A. These values correspond to 10-17 monomer units. The modeling simulations were performed for both homogalacturonan itself and homogalacturonan carrying various degrees of rhamnose inserts (rhamnogalacturonan). This required the evaluation of the accessible conformational space for the eight disaccharides that represent the constituent repeating segments of the homogalacturonan and rhamnogalacturonan polysaccharides. For each dimer, complete conformational analysis was accomplished using the flexible residue method of the MM3 molecular mechanics procedure and the results used to access the configurational statistics of representative pectic polysaccharide chains. For homogalacturonan, an extended chain conformation having a persistence length of 135 A (corresponding to 30 monomers) was predicted. The inclusion of varying amounts of rhamnose units (5-25%) in the model in strict alternating sequence with galacturonate residues (equivalent to the rhamnogalacturonan "hairy region" chains) only slightly reduced the calculated persistence length. The extended overall chain conformation remained relatively unchanged as a consequence of the self-cancellation of the kinking effects of successive paired rhamnose units.

Heat treatment applied to milk protein solutions can modify protein denaturation and aggregation state. Whey proteins (WP) are highly sensitive to heat treatment: above 70 degrees C they form aggregates or gels, while casein micelles (CM) are less affected but can complex with WP. Competitive adsorption during homogenization of milk protein stabilized emulsions leads to the formation of a heterogeneous complex layer at the interface. The aim of this study was to evaluate the effects of heat treatments (60 degrees C or 80 degrees C for 5 min) of different CM and WP aqueous mixtures (ratios from 80:20 to 12:88) on the structure of oil-water interface in relation to the texture of the emulsions. Different protein structures induced by heat treatment were characterised by light scattering and microscopy. Emulsion rheological properties were characterized and correlated with the amount of adsorbed protein, the composition and the structure of interface. Three kinds of rheological behavior and four different interfacial structures were characterized. In the first group, the emulsions were liquid, showing no connections between droplets. In the second group the emulsions were structured, the droplets being weakly connected by WP aggregated. In the third group the emulsions gelled, the droplets being connected by CM/WP complex or in other case by aggregated WP. The results are presented in a way that highlights the impact of the composition - structure relationship of the interface layer on the emulsion properties.

The rheological behaviour of xanthanguar gum systems has been investigated and compared to that of xanthanlocust bean gum mixtures using oscillatory shear and creep-recovery measurements. The total polysaccharide concentration was kept constant at 0.5% w/w, the xanthangalactomannan ratio ranged from 199 to 9010 and three ionic strengths were studied. As for xanthanlocust bean gum mixtures, strong synergistic phenomena were exhibited by xanthanguar gum systems. Clearly, the addition of xanthan gum even at a very low level to a guar gum solution induced a transition of the system from a macromolecular solution to a structured system displaying gel-like properties. The comparison between three guar gum samples with different molecular weights evidenced a strong effect of the molecular weight: the higher this parameter, the stronger the synergistic interaction. At a low xanthangalactomannan ratio (< 1090), xanthanguar gum mixtures, xanthanlocust bean gum mixtures (with comparable galactomannan molecular weights) resulted in similar viscoelastic behaviour. In contrast, at a higher xanthangalactomannan ratio, a stronger synergism was exhibited with locust bean gum, as expected. The rheological properties were greatly influenced by the presence of electrolyte. In the case of xanthanguar gum systems, the storage (G′) and the loss (G″) moduli were increased when electrolyte was present, in contrast to xanthanlocust bean gum mixtures which exhibited a reverse tendency. These results provide evidence that xanthan gum plays a major role in the rheological behaviour of the xanthangalactomannan systems even at a low concentration. Overall, similar results were found with xanthanguar or xanthanlocust bean gum mixtures. However, differences in the mechanism may exist according to the mannosegalactose ratio of the galactomannan and also to the xanthangalactomannan ratio and the ionic strength.

This article offers a historical survey of the development of Japanese language studies in France since the beginning of 19th century. It demonstrates that, at the end of the 20th century, Japanese linguistics in France could be considered a field in its own right, the subject of research by an ever-growing number of specialists hailing either from Japanese studies or linguistics. Cet article propose un panorama historique du développement des études sur la langue japonaise en France depuis le début du XIXe siècle. Il montre que, à la fin du XXe siècle, la linguistique japonaise en France peut être considérée comme un domaine à part entière, objet des recherches de spécialistes de plus en plus nombreux, issus soit des études japonaises, soit des études linguistiques.

Several studies have brought to light the difficulties which children experience in the representation and solution of change problems in mathematics. Analysis of these difficulties has uncovered certain implicit models used by children. These models actually interfere with the very process of number construction. A teaching experiment involving 30 third grade students (8- to 9-yr-olds) was developed on the basis of this analysis. According to research carried out in the Piagetian tradition, our didactic choice, within the form of a group sociomotor game, places the action of the subjects at the heart of the transformation of their concept of number. Observation of the notations and problem-solving procedures used throughout the experiment by the children in mathematical situations derived from a game enabled us to account for the children's development, which went from a focus on states to a type of reasoning in which changes become quantifiable “objects of awareness”.

Dextran/locust bean gum (LBG) mixtures have been prepared and investigated with respect to their phase separation behaviour. These systems exhibited phase separation at 20 °C, the upper phase, itself biphasic, being enriched with locust bean gum but also containing dextran, whereas the lower phase contained only dextran. This lower phase was a liquid. The upper phase, which did not flow, was characterized by means of rheological dynamic measurements. Clearly, its behaviour was typical of a gel, the three-dimensional structure of which can be ascribed to self-association of LBG chains owing to the very high concentration of the galactomannan in this upper phase. The self-association of the galactomannan was confirmed by fluorescence microscopy carried out on mixtures containing fluorescein isothiocyanate (FITC)-labelled dextran. The rheological behaviour of a concentrated LBG solution was also investigated as a function of time, clearly showing progressive formation of a weak gel structure.

According to research on mental representation carried out in the Piaget tradition (Galifret-Granjon, 1981; Piaget & Inhelder, 1966), the cognitive processes of decentration in terms of the states (initial and final) and anticipation (of change and movement) form the basis of the reconstruction of a dynamic situation. Children centered primarily on the initial and final states have great difficulty creating a mental representation of a dynamic situation. This study, based on a socio-constructivist approach (Gamier, 1985), seeks to help children develop these two fundamental processes. The pedagogical analysis focuses first on the observation of children's behaviour while playing ball in a group and then on the graphic representation of their actions drawn by the children after each play session. We saw in the children's game definite changes stemming from decentration. We also noticed that the children were centering less on the states in their graphic production which became increasingly rich in codes.

International audience; In this study, the influence of the presence of low-methoxyl pectin (LM pectin) on the rheological and microstructural properties of microfibrillated cellulose suspensions was elucidated in order to create new structures with new and interesting textures. For that purpose, the rheological properties of the cellulose/LM pectin mixtures in variable proportions were compared with those of the individual biopolymers. The influence of the presence of calcium and/or sodium ions on the properties of the mixed systems was studied. The microstructure of the resulting system was studied by transmission electron microscopy and confocal laser scanning microscopy. It was found that, in the presence of LM pectin, a synergistic effect was observed when calcium ions were also present, leading to increased rheological properties of the composites. Indeed, addition of calcium to the mixtures induced LM pectin gelation, which was favoured in the presence of sodium, the pectin network contributing to the formation of a stronger cellulose/LM pectin composite gel. The presence of LM pectin alone in the microfibrillated cellulose suspensions does not significantly modify the viscoelastic and microstructural properties of microfibrillated cellulose suspensions. Whether calcium was added to the mixtures or not in water, the viscoelastic properties of the mixtures are mainly controlled by cellulose. The same behaviour was observed for the mixtures in NaCl without added calcium. Contrary to this observation, it was noticed that in presence of both sodium and calcium ions, the viscoelastic properties of the mixtures are largely governed by LM pectin. On the other hand, it was showed that the flow behaviour of microfibrillated cellulose suspensions is modified in the presence of LM pectin with an increase in thixotropic character shear-thinning behaviour, which was more pronounced in the presence of NaCl. It was also shown, from TEM observations, that an interpenetrating network formed in cellulose/LM pectin composites gel in the presence of calcium ions. In the same way, the CLSM observations allowed the separate localization of cellulose and LM pectin within the composite systems to be highlighted. The results obtained suggests that it is possible to thus create new structures with new interesting textures, by mixing microfibrillated cellulose suspensions and LM pectin in suitable proportions in the simultaneous presence of both sodium and calcium ions.

International audience; The primary cell wall of dicotyledonous plants can be considered as a concentrated polymer assembly, containing in particular polysaccharides among which cellulose and pectins are known to be the major components. In order to understand and control the textural quality of plant-derived foods, it is highly important to elucidate the rheological and microstructural properties of these components, individually and in mixture, in order to define their implication for structural and mechanical properties of primary plant cell wall. In this study, the rheological and microstructural properties of model systems composed of sugar-beet microfibrillated cellulose and HM pectins from various sources, with varied degrees of methylation and containing different amounts of neutral sugar side chains, were investigated. The influence of the presence of calcium and/or sodium ions and the biopolymer concentrations on the properties of the mixed systems were also studied. The characterizations of the mixed system, considered as a simplified model of primary plant cell wall, showed that whatever the structural characteristics of the pectins, the ionic conditions of the medium and the biopolymer concentrations, the gelation of the composite was mainly controlled by cellulose. Thus, the cellulose network would be the principal component governing the mechanical properties of the cell walls. However, the neutral sugar side chains of the pectins seem to play a part in the interactions with cellulose, as shown by the interesting viscoelastic properties of cellulose/apple HM pectins systems. The rigidity of cellulose/pectins composite was strongly influenced by the structural characteristics of pectins. The particular properties of primary plant cell walls would thus result from the solid viscoelastic properties of cellulose, its interactions with pectins according to their structural characteristics (implication of the neutral sugar side chains and the specific potential calcic interactions) and of the distribution of the components in separate phases.