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Le défi de la bioéconomie est de concilier 3 approches différentes : les demandes et les comportements des citoyens-consommateurs, la préservation des écosystèmes et de leurs capacités de production de biens consommables et de services écosystémiques, et le croisement de la rationalité des flux verticaux (filière) de biomasses, d’énergie et d’informations à celle des usages des sols (systèmes de cultures et forestiers, villes, régions…). Suite au colloque européen sur la bioéconomie les 28 et 29 juin 2017 à Paris, rassemblant 320 personnes venant de pays européens, d’Amérique du Nord et du Sud, et d’Afrique, 5 besoins clés ont été identifiés : (a) le passage des filières au système, (b) le renforcement des leviers technologiques, organisationnels et réglementaires pour les transitions, (c) le besoin de représentations et de modélisations dans une vision à 2050, (d) des politiques publiques dédiées et (e) l’évaluation de la durabilité. 11 recommandations ont été émises pour promouvoir le développement de la bioéconomie.

International audience; Background: Agri-food is one of the most important sectors of the industry in Europe and potentially a major contributor to the global warming. Sustainability issues in this context pose a huge challenge for several reasons: the variety of considered scales, the number of disciplines involved, the uncertainties, the out-of-equilibrium states, the complex quantitative and qualitative factors, the normative issues and the availability of data. Although important insight and breakthroughs have been attained in different scientific domains, an overarching and integrated analysis of these complex problems have yet to be realized.Scope and Approach: This context creates huge opportunities for research in interaction with mathematical programming, integrative models and decision-support tools. The paper propose a computational viewpoint including questions of holistic approach, multiscale reconstruction and optimization. Some directions are discussed.Key Findings and Conclusions: Several research questions based on a mathematical programming framework are emerging: how can such a framework manage uncertainty, cope with complex qualitative and quantitative information essential for social and environmental considerations, encompass diverse scales in space and time, cope with a multivariable dynamic environment and with scarcity of data. Moreover, how can it deal with different perspectives, types of models, research goals and data produced by conceptually disjoint scientific disciplines, ranging from physics and physiology to sociology and ethics? Building models is essential, but highly difficult; it will need a strong iterative interaction combining computational intensive methods, formal reasoning and the experts of the different fields. Some future research directions are proposed, involving all those dimensions: mathematical resilience, human-machine interactive learning and optimization techniques. (C) 2015 Elsevier Ltd. All rights reserved.

Current societal challenges and recent knowledge acquisition now provide the conditions for the renewal of our collective vision of food science and technology. To meet increasingly complex challenges, it obvious that current reductionist approaches in food science must give way to a knowledge-intensive framework for function-driven research and innovation. This implies a need for more in-depth, multiscale characterization of bioresources, leading to the detailed description of functional entities (molecules, macromolecules, substructures and assemblies etc.) and the development of new transformation technologies. These must provide the underpinning knowledge to devise specific transformations, using minimal energy and water inputs, and generate the targeted end-user products. We should thus consider food manufacturing as a complex systems problem, dealing with heterogeneous product matrices (agents), changing processing conditions (environmental context), non-linear behaviour (phase changes), novel functional properties (emerging phenomena), etc. Accordingly, we propose a new research methodology and innovation agenda, hereby utilizing the knowledge that we have gained in the past decade and described in this Special Issue.

This chapter focuses on protein-based and lipid-based native nanostructures. The naturally occurring nanostructures coming from milk and eggs constitute a large part of the building blocks already used to design new nanostructures. The chapter also focuses on the description of the structure of several food proteins as they exist naturally in food. Food proteins exist mainly in the monomeric form, but are able to self-assemble into oligomers or aggregates in some specific conditions. These conditions are also addressed. The lipid droplets are spherical particles constituted by a hydrophobic core rich in triacylglycerols (TAG) covered by surfaceactive molecules such as phospholipids and proteins. These TAG-rich droplets are involved in the storage and delivery of energy. Milk fat globules have a core of TAG covered by a biological membrane composed by a trilayer of phospholipids and proteins.

International audience; Single foam films made from mixtures of nonaggregated proteins and protein aggregates have been studied using a thin film balance apparatus. Their features (heterogeneity, stability and resistance to pressure change) are dependent on the aggregate size and on the ratio between nonaggregated proteins and protein aggregates. A phase diagram of these foam films has been drawn and a correlation of the structural properties of foam film and stability of real foams has been found. In particular, the formation of a gel-like network within the foam film coincides with the stability of the corresponding 3-D foams.

International audience; The ability to adsorb at n-hexadecane - water interface of natural hydrocolloids was quantified by dynamic drop tensiometry. Conventional and matured hydrocolloids samples from Acacia senegal, Acacia seyal (AcSey), Sugar Beet Pectin (SBP) and natural untreated Gum Ghatti (GG), were studied in aqueous solutions at pH 4.5. Maturation of Acacia senegal gum (Acacia (sen) SUPERGUM(TM) EM2, designated as EM2) increased its ability to lower interfacial tension and the elastic characteristics of the interfacial film. This change in properties can be attributed to the increase in molecular weight and in arabino-galactan-protein (AGP) content. EM2 exhibited the best interfacial properties. Conventional and matured AcSey presented interfacial properties that were similar to conventional Acacia senegal (GAc), correlating with minimal changes observed in their structural features after maturation. Gum ghatti reacted similarly to EM2 and presented relatively fast kinetic profiles, revealing the good qualities of this gum. The kinetics associated with all the hydrocolloids at pH 4.5 have been described using a mathematical model, from which quantitative parameters as onset time or half-time of interfacial-tension-decrease were determined. Compared to the other hydrocolloids, SBP adsorbs by a different mechanism. However, pectin presented the lowest final interfacial tension and gave the more elastic interfacial film. Acidification of hydrocolloid solutions to pH 3.1 increased both the ability to lower the interfacial tension and the elastic characteristics of interfacial film. The effect of structural modifications on interfacial properties was demonstrated, and clarifies further the already observed emulsification behaviour of the studied hydrocolloid.

Due to the combination of flexibility and amphiphilicity, in solution β -casein ( β -CN) acts as a surfactant molecule. It undergoes self-association and forms “micellar-like” aggregates in aqueous media. The aim of our study was to understand the role played by the charges borne by the N-terminal part of β -CN in its association behavior. β -CN polarity was modified in order to induce new aggregation properties and to understand better the main factors defining them. An unphosphorylated wild type recombinant form (WT A 2 ) of β -CN has been obtained by heterologous expression in the prokaryotic host Escherichia coli. A mutant (MU A 2 ) form of β -CN was engineered by duplicating the first 6 N-terminal amino acids residues (RELEEL) of WT A 2 , three additional negatively charged glutamic acids replacing some of the negative charges lost by the absence of phosphorylation in prokaryotic expression system. Dynamic light scattering and fluorimetry experiments showed that recombinant and native β -CN have different behaviors in temperature-dependent association. Micellisation was impaired by the absence of phosphate groups. Mutation conferred to the protein the ability to form aggregates whose size is inversely proportional to the concentration. These different behaviors during the association processes displayed by recombinant β -CN are correlated with modifications of the temperature-induced compaction of the proteins, what was revealed by circular dichroism measurements. WT A 2 was less condensed at the air-water interface than native β -CN; this was in part reversed by the additive mutation. However, MU A 2 compensating the lack of phosphate charges in recombinant caseins forms a more cohesive monolayer at the air–water interface than do the other β -CN, which means that the mutation reinforces monomers interaction at the surface.

Dans le domaine des systemes emulsionnes aeres, un des enjeux majeurs est le remplacement de la gelatine, qui joue un role essentiel dans la formation et la stabilisation des mousses, par des melanges de polysaccharides. L'objectif de ce travail etait donc de comparer differentes combinaisons de polysaccharides (xanthane, carraghenane, guar, pectine, alginate) en vue de trouver le meilleur compromis possible pour fabriquer des mousses laitieres aerees stables. Nous avons demontre que les differents melanges d'hydrocolloides testes dans cette serie d'experimentations provoquent globalement une augmentation de la taille des gouttelettes de matiere grasse, une diminution de la viscosite des emulsions et une diminution de la taille des bulles d'air, en comparaison d'une mousse temoin preparee avec de la gelatine. Certains melanges d'hydrocolloides permettent d'assurer un taux de foisonnement approprie (280 %) mais, quel que soit le melange considere, la stabilite des mousses au drainage n'est pas aussi satisfaisante.

23 ref.; International audience; The interfacial behavior of oleosins, the most abundant proteins from seeds oil bodies, was investigated using the pendant drop method at water/oil interfaces and compared to the behavior of beta-casein and lysozyme, proteins with contrasted emulsifying properties. Recombined high (rS3) and low (rS4) molecular weight oleosins comprising N-terminal histidine tags were purified to electrophoretic homogeneity. rS3 decreased the interfacial tension at the oil/water interface better than rS4, oleosins being more efficient than beta-casein. Oleosins formed aggregates when spread on noncompressed phospholipid (PL) films at the air/water interface as observed using a Langmuir-Blodgett balance equipped with a Brewster angle microscope. Oleosin spread at the surface of a compressed PL monolayer (5-20 mN/m) did not aggregate. Pressure increased immediately and proportionally to the amount of protein spread on the monolayer. The results stress the capacity of oleosins to be inserted in oil and in PL monolayers, which is of particular relevancy to their potential uses as water/oil emulsifiers.

A new high pressure homogeniser going up to 350 MPa was used to produce fine emulsions stabilised by methylcellulose for food applications. The objective of this study was to evaluate the effect of homogenising pressure on emulsifying and stabilising properties of methylcellulose, a food macromolecule extensively used as stabiliser in emulsions. Oil droplet size distributions of the emulsions were measured by laser-light scattering; rheological properties were characterised with a coaxial cylinder rheometer; and stability was evaluated by heating of the emulsions. Influence of homogenising pressure on interfacial properties (adsorption kinetics, interfacial tension and rheological behaviour) of the polymer was also studied at different pressure treatments. The results showed significant modifications in the structure and the texture of emulsions with increasing homogenising pressure. Homogenised methylcellulose solutions showed weaker thickening and stabilising properties compared to the one of the native methylcellulose.

The displacement of a globular protein (bovine serum albumin, BSA) from the surface of oil droplets in concentrated oil-in-water emulsions by a nonionic surfactant (polyoxyethylene sorbitan monolauarate, Tween 20) was studied using front-face fluorescence spectroscopy (FFFS). This method relies on measurement of the change in intensity (I(MAX)) and wavelength (lambda(MAX)) of the maximum in the tryptophan emission spectrum. A series of oil-in-water emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7.0) containing different molar ratios of Tween 20 to BSA (R = 0-131) were prepared. As the surfactant concentration was increased, the protein was progressively displaced from the droplet surfaces. At Ror = 66, the protein was completely displaced from the droplet surfaces. There was an increase in both I(MAX) and lambda(MAX) with increasing Tween 20 concentration up to R = 66, which correlated with the increase in the ratio of nonadsorbed to adsorbed protein. In contrast, there was a decrease in I(MAX) and lambda(MAX) with Tween 20 concentration in protein solutions and for Ror = 66 in the emulsions, which was attributed to binding of the surfactant to the protein. This study shows that FFFS is a powerful technique for nondestructively providing information about the interfacial composition of droplets in concentrated protein-stabilized emulsions in situ. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.

Initially developed for the dairy industry, the very high pressure homogenisation (>100 MPa) is now also applied in the pharmaceutical sector and in biotechnology (breaking cells for biomass extraction). The use of this technology to make fine food emulsions and to modify functional properties of macromolecules seems to be promising. Thus the objective of this study was to understand the effect of homogenisation forces on the mechanical degradation of a model polymer extensively used in food, cosmetic and pharmaceutical preparations: the methylcellulose. Degradation of the polymer was studied in a pressure range in the homogenising valve from 20 to 350 MPa. It was observed that as the pressure imposed by the homogeniser increased, the intrinsic viscosity decreased. Intrinsic viscosity decrease was correlated to apparent changes in the average molecular weight of the polymers obtained by size exclusion chromatography coupled on-line with multi-angle laser light scattering and refractive index detection (SEC/MALLS/RI). The strong elongational flow encountered by the polymer at the entrance of the valve of the high pressure homogeniser device may bring sufficient energy to disrupt covalent bonds. Consequently, as shown by flow behaviour the thickening properties of this polymer were also reduced.

Cream cheese is a good model for studying the effect of process and formulation changes on the modification of product texture. In this study, the intensity of heat treatment (72 degrees C/20 s or 94 degrees C/40 s), the final pH of acidification (pH 5.2 or 4.9) and the homogenization pressure (0, 5, 20, or 60 MPa) were studied. Special attention was paid to the whey protein denaturation, casein micelle dissociation, fat globule size and their relations with structural, rheological, and sensory characteristics of the cream cheese model. Rheological properties of final cream cheese mainly depended on homogenization pressure. Increasing the homogenization pressure led to a decrease in fat globule size and consequently in an increase in the cream cheese firmness. This result was modulated by heat treatment temperature and the subsequent whey protein denaturation. Cream cheese final pH between 5.2 and 4.9 had a low impact on rheological properties but was the most discriminating factor for sensory perception by strongly affecting product appearance especially its brightness and its shade.

The emulsifying and oil-in-water stabilizing properties of methylcellulose (MeC) were investigated in bovine serum albumin (BSA)-based emulsions. The creaming stability, flocculation, surface concentration of BSA and MeC and droplet size were determined. Results obtained showed modifications of creaming rates that were related to MeC concentrations in the continuous and dispersed phases. Viscosity effects on creaming and changes in average droplet size (d43) relating to droplet coverage were identified and delineated. Studies performed on macroscopic oil–water and air–water interfaces were used to identify interfacial structuring and composition. A good agreement was found between droplet surface composition and the resistance to coalescence of emulsion droplets. Emulsions that demonstrated a more rigid-like adsorbed interfacial layer were more stable with respect to coalescence. This study involving model emulsion systems provides a new insight into the stability of industrial preparations containing mixtures of proteins and polysaccharides.

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.

Small-angle neutron scattering measurements were used for structural investigation of β-lactoglobulin solutions and heat-set gels in conditions of strong double layer repulsions. At pH 9 and low ionic strength, a correlation peak was observed on the scattering curves of the solutions whatever the protein concentration C used (in the range C = 0.02–0.10 g/mL). The wave vector value qmax corresponding to these maxima scaled as C0.25. This exponent value is in agreement with those reported in the literature for other globular proteins in the same concentration range. Increasing the ionic strength decreased the peak which vanished without changing position at 0.1M NaCl. This polyelectrolyte-like behaviour suggests a local structure in the protein solution due to double layer repulsions. In the case of heat-set aggregates and gels (0.02–0.13 g/mL) formed at pH 9 and low ionic strength, a peak in the scattering curves was also observed indicating that even after gelation a correlation is still present; qmax varied as C0.5. As in the case of the solutions, the correlation peak decreased with increasing ionic strength, and it vanished at 0.06M NaCl. The dilution of the aggregates in order to determine their intraparticle structure factor showed that the correlations were lost and that the aggregates displayed the same internal structure as the elementary subunit in the gels. At high ionic strength, fractal structures of the aggregates down to a length scale of about 40 A were observed with df = 1.3–1.75 ± 0.05, increasing with protein concentration. Subsequent dilution didn't change the fractal dimension of these structures. © 1996 John Wiley & Sons, Inc.

Binding of some divalent cations (Ca 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Pb 2+ and Zn 2+ ) in aqueous solution by saponified and cross-linked sugar-beet pulp was investigated. Saponification doubled the cation-exchange capacity, while cross-linking decreased specific surface area and hydration properties to low and stable values independent of pH and ionic strength conditions. The sorption isotherms indicated a high metal-binding capacity which increased with sorbent concentration, and followed a clear order of selectivity: Cu 2+ ~Pb 2+ ⪢ Zn 2+ ~Cd 2+ > Ni 2+ > Ca 2+ . The sorption data were better represented by the Langmuir isotherm than by the Freundlich one, suggesting that the monolayer sorption, mainly due to ion-exchange, would not be disturbed by lateral interactions between cations sorbed with similar sorption energies. The same order of selectivity could be drawn from the Langmuir parameters, sorption equilibrium constants ( K L ) and maximum binding capacities (Me A max). Whatever the cation, K L decreased with increasing sorbent concentration, while Me b max increased. Higher quantities of Cu 2+ and Pb 2+ than predicted by the one divalent cation to two carboxyl functions ratio were bound. This was attributed to the partial contribution to the sorption phenomenon of hydroxyl functions close to ionic sites, explaining the higher affinity of such cations for substrates. Cross-linked pulp exhibited higher metalbinding capacity per volume unit than the raw pulp.

Saponification and cross-linking by formaldehyde and epichlorohydrin were performed on beet pulp in order to improve its potentialities as an ion-exchanger, either by increasing its cation-exchange capacity and/or by decreasing its hydration capacities. Effects of the treatments on sugar composition, on swelling and waterretention capacities, and on the binding of two metal cations (Zn2+ and Pb2+) are reported. Saponification doubled the cation-exchange capacity without modifying the sugar composition or decreasing the hydration properties. The swelling capacity was thus identical to that of the initial pulp (~32 ml g−1 at pH~7 in water). Treatment with formaldehyde had little effects on the hydration properties. The best results in terms of hydration properties were obtained with epichlorohydrin, which lowered the swelling and water-retention capacities to 7 ml g−1 and 2 g g−1, respectively, independently of pH and ionic strength. Binding properties were not altered by this treatment. However, the conditions used led to major changes in sugar composition, with severe loss of pectins at the lower epichlorohydrin levels. This loss was reduced at higher levels of epichlorohydrin, suggesting that pectins were involved in the crosslinking. Binding properties were not altered by such a treatment.

The binding of divalent metal cations (Ca2+, Cd2+, Cu2+, Ni2+, Pb2+ and Zn2+) by sugar-beet pulp was studied. In the presence of 0.1 m NaNO3 the level of metal cation uptake was found to reach its maximum value very rapidly with the speed increasing both with the sugar-beet pulp concentration and with increasing initial pH of the suspension. Using a pH-metric method and by comparing binding isotherms drawn by measuring the free cation concentration after equilibration, a clear scale of decreasing selectivity was found as follows: Cu2+~Pb2+⪢Cd2+~Zn2+ > Ni2+ > Ca2+. Binding followed the Langmuir-type isotherm except for Ca2+. Adsorption may contribute to the binding phenomenon in addition to ion exchange, which may include electrostatic interactions and even chelation in the case of the more strongly bound cations. Sugar-beet pulp, which is cheap and highly selective, therefore seems to be a promising substrate to entrap heavy metals in aqueous solutions.

Phase separation and gelation induced by addition of monovalent and divalent cations in iota and kappa carrageenan solutions were investigated as a function of the polymer and cation concentrations. Rheological measurements have also been carried out at a given polymer concentration. The storage modulus (G') determined at a cation/polymer ratio was always higher for kappa- than for iota-carrageenan. For iota carrageenan, G' increased slowly with the monovalent salt concentration and more quickly with the divalent salt concentration. At the opposite, for kappa carrageenan, G' increased more rapidly in the presence of KCl than with calcium or copper. Nevertheless for large salt concentrations, G' became independent of the type and concentration of cations in the kappa carrageenan solution.

We report on the structure of whey protein aggregates formed by a short heating coupled to shear at high temperatures (80-120) and neutral pH in scale-up processing conditions, using gel filtration chromatography, light scattering, small angle neutron scattering, and cryogenic transmission electron microscopy. The results are interpreted in terms of coexistence of residual non-aggregated proteins and aggregates. The characteristics of aggregates such as the size, the aggregation number and the shape evidence two different morphologies. Whereas aggregates formed at 80 °C show a selfsimilar structure down to a length scale of the monomer with a fractal dimension typical for reaction limited cluster aggregation (D~2.2), aggregates formed at higher temperature show a spherical morphology, with the structure from small angle neutron scattering data best modelled with the form factor of a polydisperse sphere. We compare the structure of these aggregates to that of aggregates formed in quiescent conditions at lab scale. The structure transition is interpreted in terms of a non-trivial interplay between three perturbation factors: interparticle interaction, temperature and shear.

A scale of selectivity for the binding of calcium and some heavy metal ions by citrus and sugar-beet pectins was set up by pH-measurements. The same order of selectivity was found for the two pectins, decreasing as follows: Cu 2+ ∼ Pb 2+ ⪢ Zn 2+ > Cd 2+ ∼ Ni 2+ ≥ Ca 2+ . Binding isotherms for Ca 2+ , Cu 2+ , Ni 2+ , Pb 2+ and Zn 2+ ions have shown a greater binding level when the ionic strength decreased and when the pectin concentration increased in the presence of 0.1 M NaNO 3 . By comparing binding isotherms, the same order of selectivity was found as by pH-studies. Scatchard plots and Hill index evaluation showed for all ions and all pectins anticooperative interactions in water. In the presence of 0.1 M NaNO 3 , citrus pectins displayed cooperative interactions for all metal ions. In contrast, for sugar-beet pectins, cooperative interactions only occured with Cu 2+ and Pb 2+ . With Ca 2+ , Ni 2+ and Zn 2+ sugar-beet pectins displayed Scatchard plots which could not be distinguished from an anticooperative binding. This difference of behaviour could be related to the presence of acetyl groups decreasing the affinity of Me 2+ for sugar-beet pectins.

Resume De l’insuffisance a l’exces de nourriture differentes formes de malnutrition coexistent dont les determinants sont multiples. Ameliorer l’etat nutritionnel des populations est donc un imperatif de sante publique a l’echelle de la planete qui s’accompagne d’un defieconomique. Si le developpement d’un systeme agro-industriel ces soixante dernieres annees a sans nul doute facilite l’acces a une nourriture plus sure il a aussi contribue a la diffusion de produits trop gras et trop sucres. Concevoir des aliments ayant un benefice sante et accessibles a tous est donc le defia relever. Cela necessite de developper une ingenierie des aliments pour accroitre nos connaissances sur les relations ingredientsproduits – procedes puis de comprendre les mecanismes de deconstruction des aliments en lien avec la biodisponibilite des molecules actives et enfin d’integrer cet ensemble de connaissances dans des modeles mathematiques qui permettront d’elaborer des outils d’aide a la decision en prenant en compte de nombreux criteres.

Phase separation and gelation phenomena induced by addition of divalent cations in aqueous solutions of synthetic and natural polycarboxylates have been investigated by comparison of their phase diagrams. Three major types of behavior may be identified on the basis of the position and shape of the demixing line in the phase diagram, regardless of the chemical structure of the polymer. We propose a model for quantitative prediction of the demixing and sol-gel transition. The relevant parameters introduced are the neutral units, the charge density, and the cation/polyanion affinity, all of which are responsible for inter- and intramolecular complexes. Besides this general scheme, the local configuration of the backbone in natural polymers seems to promote intermolecular cross-links, leading to a large gel phase.

The amount of water-soluble pectins was largely increased after extrusion-cooking of lemon fibres. These pectins showed the ability to form a gel in the presence of sucrose and at acidic pH. The gels obtained with the water-extracted pectins after extrusion-cooking and with pectins acid-extracted on a laboratory scale were softer than those prepared with commercial citrus pectins. The water-extracted pectins after extrusion-cooking and the pectins acid-extracted on a laboratory scale contained long neutral side-chains and required a higher sucrose concentration to gel than the commercial citrus pectins. The extruded lemon fibres showed the ability to form gels in the presence of sucrose and at acidic pH. The gels obtained with the extruded fibres containing some water-solube pectins of high molecular weight were stronger than those obtained with the extruded fibres containing higher amounts of more depolymerised water-soluble pectins. The extruded fibres containing 12.5–14.9% of water-soluble pectins of high molecular weight (intrinsic viscosity: 413–504 mL/g) were those showing the better gelation properties.

The degradation of pectins in aqueous (NaCl 0.1 mol/dm3 initial pH 7) non-buffered solutions increases with temperature and methyl content when evaluated from the evolution of the specific viscosity versus time. Approximating the initial phase of the degradation by a first order kinetics, the activation energies for the β elimination are respectively estimated as 93 and 68 kJmol−1 for pectins with a degree of esterification of 72 and 28%. The intrinsic viscosity of pectins with different degrees of esterification, in 0.1 mol/dm3 NaCl aqueous solutions, is found to decrease as temperature increases. Assuming that the effect of excluded volume is predominant over the intrinsic conformational change of the backbone with temperature, the Huggins coefficient is found to be a decreasing function of the expansion factor α3.

The effects of ionic strength, pH, and temperature on the gelation of pectin-calcium systems were studied on an apple pectin; the influence of the degree of methylation (dm) was investigated on a family of well-characterised citrus pectins obtained by acid-catalyzed deesterification. The reaction led to a decrease in intrinsic viscosities by hydrolysis of glycosidic bonds and in neutral sugar content by elimination of the neutral fraction. Ion-exchange chromatography indicated that the deesterification did not change the charge distribution along the pectic backbone, which was confirmed by potentiometric and conductimetric studies. These methods showed that the charge distribution was statistical in apple and citrus pectins and that no egg-box can occur. Phase diagrams (sol-gel-syneresis), established as calcium concentration versus reduced polymer concentration, showed that gelation was possible before the overlapping of chains because of the strong interactions of calcium with pectins. An increase in the ionic strength, a neutral pH, and a decrease in the setting temperature and in the dm lower the amount of calcium required to give a gel, which can be explained by changes in the probability of crosslinks. Syneresis appeared at relatively low concentrations of calcium.

Water-soluble polysaccharides (12·2% of the algal dry weight) were extracted from marine green seaweed ( Ulva spp.) which proliferate along the Brittany shores of France. They were composed of 18·4% rhamnose, 4·4% glucose, 1·9% xylose, 0·9% mannose, 0·9% galactose, 15·2% uronic acid, 15·8% sulphate and 23·7% ash based on the extract dry weight. These polysaccharides, formed a weak gel (about 3 Pa) at a concentration of 1·6% (w/v) in deionized water. The elastic modulus increased to about 160 Pa when boric acid (15–33 m m ) was added and reached 250 Pa when both boric acid (7 m m ) and calcium chloride (7 m m ) were present. Adjusting the pH to 7·5 or higher by sodium tetraborate, phosphate or Tris-HCl buffers was detrimental to the gel. These results demonstrate that the poorly exploited biomass of Ulva spp. is a source of gelling polysaccharides of potential economical value. Mechanisms for gel formation which unusually involve both boron and calcium ions are proposed and will be studied further.

The different susceptibilities to acid hydrolysis of the glycosidic linkages in a pectin backbone were used to isolate fractions corresponding to the “smooth”, homo-d-galacturonic regions. Pectins from apple, beet, and citrus were de-esterified, and the resulting pectic acids were hydrolysed in 0.1 M HCl at 80°C for up to 72 h. The intrinsic viscosities of the hydrolysates decreased, and two stages could be distinguished. Up to 10 h, there was a fast decrease, corresponding to the cleavage of the more susceptible linkages between l-rhamnose and galacturonic acid residues, followed by a slower stage, corresponding to cleavage of the linkages between galacturonic acid residues. During the course of the reaction, some galacturonic acid and most of the neutral sugars were solubilised, giving two fractions on Sepharose CL-6B. A minor fraction, composed mostly of galacturonic acid and rhamnose, with rhamnose-galacturonic acid ratios of 1:1.5, 1:2.9, and 1:2.1 for apple, beet, and citrus, respectively, eluted at Kav 0.8, and a major fraction, composed essentially of l-arabinose and d-galactose, eluted at the total volume. The acid-insoluble materials represented 84, 66, and 90% of the original pectic acids for apple, beet, and citrus, respectively. They were progressively freed of neutral sugars; after hydrolysis for 72 h, almost pure polygalacturonates (more than 98 mol% galacturonic acid), representing the homogalacturonic regions, were obtained. The molecular weights of these 72-h acid-insoluble materials from apple, beet, and citrus were similar (respectively, 21000, 19000, and 24000), corresponding to lengths of the homgalacturonic regions estimated to be a minimum of 72–100 galacturonic acid residues.

International audience; Calcium phosphate ceramics are widely used as bone substitutes in dentistry and orthopedic applications. For minimally invasive surgery an injectable calcium phosphate ceramic suspension (ICPCS) was developed. It consists in a biopolymer (hydroxypropylmethylcellulose: HPMC) as matrix and bioactive calcium phosphate ceramics (biphasic calcium phosphate: BCP) as fillers. The stability of the suspension is essential to this generation of "ready to use" injectable biomaterial. But, during storage, the particles settle down. The engineering sciences have long been interested in models describing the settling (or sedimentation) of particles in viscous fluids. Our work is dedicated to the comprehension of the effect of the formulation on the stability of calcium phosphate suspension before and after steam sterilization. The rheological characterization revealed the macromolecular behavior of the suspending medium. The investigations of settling kinetics showed the influence of the BCP particle size and the HPMC concentration on the settling velocity and sediment compactness before and after sterilization. To decrease the sedimentation process, the granule size has to be smaller and the polymer concentration has to increase. A much lower sedimentation velocity, as compared to Stokes law, is observed and interpreted in terms of interactions between the polymer network in solution and the particles. This experimentation highlights the granules spacer property of hydrophilic macromolecules that is a key issue for interconnection control, one of the better ways to improve osteoconduction and bioactivity.

International audience; The foaming properties, foaming capacity and foam stability, of soluble complexes of pectin and a globular protein, napin, have been investigated with a “Foamscan” apparatus. Complementary, we also used SANS with a recent method consisting in an analogy between the SANS by foams and the neutron reflectivity of films to measure in situ film thickness of foams. The effect of ionic strength, of protein concentration and of charge density of the pectin has been analysed. Whereas the foam stability is improved for samples containing soluble complexes, no effect has been noticed on the foam film thickness, which is almost around 315 Å whatever the samples. These results let us specify the role of each specie in the mixture: free proteins contribute to the foaming capacity, provided the initial free protein content in the bulk is sufficient to allow the foam formation, and soluble complexes slow down the drainage by their presence in the Plateau borders, which finally results in the stabilisation of foams.

International audience; We investigated the structure of heat-induced assemblies of whey globular proteins using small angle neutron scattering (SANS), static and dynamic light scattering (SLS and DLS), and cryogenic transmission electron microscopy (Cryo-TEM). Whey protein molecules self-assemble in fractal aggregates with a structure density depending on the electrostatic interactions. We determined the static and dynamic properties of interfacial layer formed by the protein assemblies, upon adsorption and spreading at the air-water interface using surface film balance and interfacial dilatational rheology. Upon spreading, all whey protein systems show a power-law scaling behavior of the surface pressure versus concentration in the semi-dilute surface concentration regime, with an exponent ranging from 5.5 to 9 depending on the electrostatic interactions and the aggregation state. The dilatational modulus derived from surface pressure isotherms shows a main peak at 6-8 mN/m, generally considered to be the onset of a conformational change in the monolayer, and a second peak or a shoulder at 15 mN/m. Long-time adsorption kinetics give similar results for both the native whey proteins and the corresponding self-similar assemblies, with a systematic effect of the ionic strength

Single foam films made from aqueous protein solutions containing aggregates have been studied using a thin film balance apparatus. When the solutions are free from non-aggregated proteins, the films are either fluid or gelified, depending on the aggregate size. When non-aggregated proteins are present, they adsorb at the film surfaces, acting as anchors for the aggregates, and ultimately leading to stable foam films if the amount of non-aggregated proteins is sufficient. In all cases, gel-like films are more stable than fluid films and there is a good correlation between foam and film stability.

International audience; We report on three-dimensional Monte Carlo simulations of dilute solutions of multiblock copolymers made of regularly spaced hydrophobic and hydrophilic blocks in the limit of long chains with a large number of blocks. Using a lattice model we investigate the effects of the ratio of hydrophobic to hydrophilic block lengths and impact of the quality of the solvent on the intramolecular structure of the copolymers. In poor solvent and for given block lengths the simulations show evidence for the existence of different kinds of intramolecular self-assemblies depending on solvent quality: Micelles, chains of micelles, tubes, and layered structures are revealed by both statistical properties and visualization. The form factor signature of the different structures has been identified and is discussed in connection with its experimental observability. The existence region of the different conformations in terms of energy and entropy is summarized in a phase diagram.

International audience; The present paper investigates the rheological properties of silated hydroxypropylmethylcellulose (Si-HPMC) biohydrogel used for biomaterials and tissue engineering applications. The general property of this modified cellulose ether is the occurrence of self-hardening due to silanol condensation subsequent to a decrease in pH (from 12.4 to nearly 7.4). The behavior of unsterilized and sterilized Si-HPMC solutions in diluted and concentrated domains is first described and compared. In addition, the influence of physiological parameters such as pH and temperature on the rate of the gelation process is studied. In dilute solution, the intrinsic viscosity ([eta]) of different pre-steam sterilization Si-HPMC solutions indicates that macromolecular chains occupy a larger hydrodynamic volume than the post-steam sterilization Si-HPMC solutions. Although the unsterilized Si-HPMC solutions demonstrate no detectable influence of pH upon the rheological behavior, a decrease in the limiting viscosities (eta(0)) of solutions with increasing pH is observed following steam sterilization. This effect can be explained by the formation of intra- and intermolecular associations during the sterilization stage originating from the temperature-induced phase separation. The formation of Si-HPMC hydrogels from injectable aqueous solution is studied after neutralization by different acid buffers leading to various final pHs. Gelation time (t(gel)) decreases when pH increases (t(gel) varies from 872 to 11s at pH 7.4 and 11.8, respectively). The same effect is observed by increasing the temperature from 20 to 45 degrees C. This is a consequence of the synergistic effect of the increased reaction rate and acid buffer diffusion. pH and temperature are important parameters in the gelation process and their influence is a key factor in controlling gelation time. By adapting the gel parameters one could propose hydrogels with cross-linking properties adapted to clinical applications by controlling the amount of pH of neutralization and temperature.

The influence of temperature on the equilibrium shear modulus of low-methoxyl pectin—calcium gels have been investigated in order to determine the standard breakdown enthalpy of the gel crosslinks and the activation energy of the polymer chain relaxation process.

ResumeLes pectines sont des polymeres glucidiques largement presents dans les parois vegetales dont aucune definition claire n'existe. Elles sont etudiees par des biochimistes, des biologistes, des pathologistes, des physicochimistes, des technologues avec des approches ou des methodes differentes. Il existe un certain nombre de difficultes qui sont rencontrees quelle que soit l'approche choisie. Ces difficultes sont dues a trois facteurs principaux: (1) les pectines sont des polymeres portant des charges electriques qui influent notablement sur la solubilite, ses degradations chimiques, les chromatographies et le comportement en solution (2) les pectines sont des polysaccharides dont la determination de la composition monomerique et l'analyse structurale sont rendues difficiles par le caractere heteropolymerique et (3) l'etape d'extraction, necessaire pour pouvoir les etudier, rend obligatoire certaines precautions de maniere a minimiser les artefacts. Tous ces aspects seront discutes.

International audience; Silated hydroxypropylmethylcellulose (Si-HPMC) is a modified biopolymer used in biomaterial's domain. A hydroxypropylmethylcellulose (HPMC) was functionalised with silane groups. The macromolecular solution of Si-HPMC (pH 12.9) generates an elastic state at physiological pH (~7.4). In this work we present the gel formation of Si-HPMC resulting from the condensation of silanol groups. The crosslinked hydrogel was characterized using rheological techniques. With the scalar percolation model the gelation time was determined as a function of Si-HPMC concentration at 37 °C.

International audience; This paper describes the rheological properties of silated hydroxypropylmethylcellulose (HPMC-Si) used in biomaterials domain as a three-dimensional synthetic matrix for tissue engineering. The HPMC-Si is an HPMC grafted with 3-glycidoxypropyltrimethoxysilane (GPTMS). HPMC and HPMC-Si were studied. It is shown that although silanization reduces the hydrodynamic volume in dilute solution, it does not affect significantly the rheological behavior of the concentrated solutions. The HPMC-Si viscous solution (pH 12.8) cross-links by decreasing the pH using an acid buffer, since HPMC-Si solution transforms into an elastic state. The kinetics of cross-linking and final elastic properties is influenced by several parameters such as polymer concentration, pH and temperature. pH and temperature play an important role in the silanol condensation, mainly responsible for network formation. The study of the gelation process revealed the dependence of the final concentration of HPMC-Si hydrogel on cross-linking kinetics and viscoelastic properties. The percolation theory was applied to determine gel point and to discuss the dependence of storage (G') and loss (G'') moduli on frequency. Results showed that both G' and G'' exhibit a power-law behavior with an exponent (0.68) which extends over the entire frequency range. This method is the only one to characterize the time where a liquid viscous phase shifts to hydrogel with elastic properties. In this case it was about 23 min for a final pH of 7.4.

International audience; Our paper aims at determining the respective part of protein aggregates and non-aggregated proteins in the foam formation and stability of P-lactoglobulin. We report results on fractal aggregates formed at neutral pH and strong ionic strength (aggregates size from 30 to 190 nm). Pure aggregates and mixtures of non-aggregated/aggregated proteins at varying ratios were used. The capacity of aggregates to form and stabilize foams has been studied in relation with their ability to absorb at air/water interfaces. Our results show that protein aggregates are not able by themselves to improve the foaming properties but participate to a better foam stabilization in the presence of non-aggregated proteins. Non-aggregated proteins appear to be necessary to produce stable foams. We have shown that the amount and the size of aggregates had an influence on the drainage rate.

Pectins with degree of methylation lower than 50% are able to gel in presence of divalent ions such as calcium. A phase diagram of a sodium pectinate (DM=28%) in wate, pH 7.4, and 20°C was established, evidencing three phases: sol, gel, and syneresis. From rheological experiments, the calcium concentration at the sol-gel transition was determined, [Ca2+]t/[COO−] ≈ 0.168, for a polymer concentration of 5.8 g/l and it was shown that this transition was accurately described by the scalar percolation theory. Under the same conditions, potentiometric studies showed that the binding of calcium ions seemed to be independent from physical state (sol or gel). Furthermore, this calcium binding decreased only slightly with the amount of added calcium, whereas the sodium one decreased sharply in the same time. By following the evolution of the 23Na NMR longitudinal relaxation time, and abrupt increase was found around [Ca2+]t[COO−]=0.182, which was close to the results of the rheological study.

20. International Symposium on Ceramics in Medicine du 24-26 octobre 2007; Nantes, FRANCE; International audience; Injectable calcium phosphate (CaP) biomaterial is considered as an injectable bone substitute (IBS). It was developed to minimize invasive surgery in various applications in orthopedic and dental surgery. The IBS considered of a polymer solution mixed with biphasic calcium phosphate (BCP) ceramic particles. Two particle sizes of BCP (40-80 and 80-200μm) were used and the weight ratio was 40%. This study investigated the influence of polymer solution on the BCP particles stability. Effects of particles size and limiting viscosity of polymer on the sedimentation were studied. The polymer concentration and particles size can be adapted to provide the best stability and storage of IBS.

International audience; We report on small angle neutron and X-ray scattering experiments on single common black films in ordered bamboo foams stabilized by sodium dodecyl sulfate and dodecanol. We observed anisotropic scattering perpendicular to the film. The integrated signal exhibits clear Kiessig fringes over a wide range of diffusion vector q. We were able to fit our data by a single layer (neutron with contrast matching water/SDS) or a "three slabs" (X-ray) reflectivity. We also discuss about the wide range of reflected angle, despite the narrow distribution of incident angles. Though thermal surface fluctuations may induce off-specular reflectivity, we show here a simple geometrical explanation of the phenomenon. This angle distribution is indeed compatible with the curvature of the film.

International audience; The sol-gel transition of biopolymer mixtures has been investigated by rheological and ultrasonic measurements. A scaling analysis of the data was performed for both types of measurements. A gel time was determined from rheology for the pure pectin samples, and the data could be fitted to a universal scaling form near the transition point. Its critical exponents are in good agreement with the predictions of scalar percolation theory. In addition, the ultrasonic signal of the pectin samples close to the transition was analyzed in terms of a high-frequency scaling approach for the attenuation and the velocity. For the alginate samples and the mixtures, for which the gel point cannot be determined reliably from rheology, the ultrasonic measurements were analyzed using the same scaling form as for the pectin sample, thus providing a method for estimating the gel point, even in the absence of rheological data.

Measurement of the intensity (I(MAX)) and/or wavelength (lambda(MAX)) of the maximum in the tryptophan (TRP) emission spectrum using front-face fluorescence spectroscopy (FFFS) can be used to provide information about the molecular environment of proteins in nondiluted emulsions. Many protein-stabilized emulsions in the food industry are flocculated, and therefore, we examined the influence of droplet flocculation on FFFS. Stock oil-in-water emulsions stabilized by bovine serum albumin were prepared by high-pressure valve homogenization (30 wt % n-hexadecane, 0.35 wt % BSA, pH 7). These emulsions were used to create model systems with different degrees of droplet flocculation, either by changing the pH, adding surfactant, or adding xanthan. Emulsions (21 wt % n-hexadecane, 0.22 wt % BSA) with different pH (5 and 7) and molar ratios of Tween 20 to BSA (R = 0-131) were prepared by dilution of the stock emulsion. As the surfactant concentration was increased, the protein was displaced from the droplet surfaces, which caused an increase in both I(MAX) and lambda(MAX), because of the change in TRP environment. The dependence of I(MAX) and lambda(MAX) on surfactant concentration followed a similar pattern in emulsions that were initially flocculated (pH 5) and nonflocculated (pH 7). Relatively small changes in FFFS emission spectra were observed in emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7) with different levels of depletion flocculation induced by adding xanthan. These results suggested that droplet flocculation did not have a major impact on FFFS. This study shows that FFFS is a powerful technique for nondestructively providing information about the molecular environment of proteins in concentrated and flocculated protein-stabilized emulsions. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.

We report on the interaction, in solution, between a wheat lipid transfer protein (LTP1) and three telechelic polymers, constituted by a polyethylene oxide (PEO) unit of 20, 32 or 35 kDa and end-capped with either palmitic or stearic alkyl chains. These polymers were used as models of the plant polymers, cutin and suberin, which are constituted by esterified hydroxyl-fatty acids. Steady state fluorescence measurement reveal that the protein can bind all these telechelic polymers with a stoichiometry of one polymer per protein, that is, two alkyl chains. This suggests that LTP1 can interconnect alkyl polymers in solution forming macromolecular assemblies. These aggregates were further studied in the case of PEO 32 kDa end-capped with palmitic alkyl chains at the air/water interface by using surface pressure measurements and Brewster angle microscopy (BAM). The presence of domains revealed that aggregates were surface active but were removed from the interface at high surface pressure. This is consistent with the fact that the bound protein masks the alkyl chains making the hydrophobically modified polymer more soluble. Altogether, these results provide evidence that LTP1 could link in a non-covalent way several oligomers in solution and at an interface forming aggregates of macromolecular complexes.

Two alkali-soluble polysaccharide fractions from the cell wall of Ulva ‘rigida’ were determined to be β-1,4-linked glucoxylans and a β–1,4-linked glucuronan by chemical and NMR spectroscopic analysis. The 13C NMR spectrum of water-soluble xyloglucuronorhamnan sulfate from Ulva ‘rigida’ referred to as ulvan is reported and the 13C and 1H NMR chemical shifts of its major repeating unit, the aldobiuronic acid β-D-GlcA-(1,4)-L-Rha, are given. The composition and gelling properties of ulvan from Ulva species from ‘green tides’ are also reported. The thermoreversible gel required both calcium and borate ions and the shear storage modulus G’ was ion concentration dependent. The mechanism of gelation and the associations of the different Ulva cell wall soluble polysaccharides are discussed.