Monique Axelos - Academia.edu (original) (raw)

Papers by Monique Axelos

Research paper thumbnail of SEC−MALLS and SANS Studies Applied to Solution Behavior of Linear α-Glucans

Macromolecules, 2000

Both size-exclusion chromatography coupled on-line with multiangle-laser-light-scattering (SEC−MA... more Both size-exclusion chromatography coupled on-line with multiangle-laser-light-scattering (SEC−MALLS) and small-angle neutron scattering (SANS) demonstrate that linear α-glucan chains adopt the conformation of random coils with a higher dimension in alkaline ...

Research paper thumbnail of Effect of galactomannans on the viscoelastic behaviour of pectin/calcium networks

Polymer Gels and Networks, 1996

Research paper thumbnail of Effect of heat treatment, final pH of acidification, and homogenization pressure on the texture properties of cream cheese

Dairy Science & Technology, 2014

Research paper thumbnail of Heavy metals binding by pectins: selectivity, quantification and characterisation

Progress in Biotechnology, 1996

Citrus and sugar-beet pectins with similar degrees of methylation were put in contact with divale... more Citrus and sugar-beet pectins with similar degrees of methylation were put in contact with divalent metal ions in presence of 0.1M NaNO3 or in pure water. pH studies and binding isotherms allowed to establish the same scale of selectivity for both pectins, decreasing as follows: Cu2+∼Pb2+≫Zn2+≥Cd2+∼Ni2+>Ca2+. Binding isotherms showed the same features for both pectins according to the ionic strength,

Research paper thumbnail of Surface and Interfacial Properties of Natural Hydrocolloid Emulsifiers

Research paper thumbnail of Interactions of pectins with multivalent cations: Phase diagrams and structural aspects

Progress in Biotechnology, 1996

... Sci., 13 (1954) 43. 27 JF Joanny and L. Leibler, J. Phys. ... Rev. Lett., 64 (1990) 1457. 35 ... more ... Sci., 13 (1954) 43. 27 JF Joanny and L. Leibler, J. Phys. ... Rev. Lett., 64 (1990) 1457. 35 MAV Axelos, MM Mestdagh, unplubished results 36 S. Cros, C. Garnier, MAV Axelos, A. Imberty, S. Perez, Biopolymers (1996) 37 BA Burton and DA Brant, Biopolymers, 22 (1983) 1769. ...

Research paper thumbnail of In Situ Investigations on Organic Foam Films Using Neutron and Synchrotron Radiation

Langmuir, 2005

We report on small-angle neutron scattering (SANS) and X-ray scattering (SAXS) investigations of ... more We report on small-angle neutron scattering (SANS) and X-ray scattering (SAXS) investigations of foam films stabilized by sodium dodecyl sulfate. Previous measurements on dry foams (Axelos, M. A. V.; Boué, B. Langmuir 2003, 19, 6598) have shown the presence of spikes in the two-dimensional scattering data which suggest that the incident beam is reflected on some film surfaces. The latter interpretation is confirmed by new neutron studies performed on ordered ("bamboo") foams which allow selection of single films. In the first case, we show that the spikes of the scattered intensity can be obtained by reflection on two parts of the foam, namely, the films and the Plateau borders. With synchrotron radiation, first observations of distinct interference fringes have allowed an accurate determination of the film thickness. A comparison with X-ray and neutron data is made, opening a general discussion about the capabilities of small-angle scattering techniques for studying the microscopic properties of foam films.

Research paper thumbnail of Foams As Viewed by Small-Angle Neutron Scattering

Research paper thumbnail of Self-Assembly of Fatty Acids and Hydroxyl Derivative Salts

Langmuir, 2008

We report the dispersions of a fatty acid and hydroxyl derivative salts in aqueous solutions that... more We report the dispersions of a fatty acid and hydroxyl derivative salts in aqueous solutions that were further used to produce foams and emulsions. The tetrabutyl-ammonium salts of palmitic acid, 12-hydroxy stearic acid, and omega-hydroxy palmitic acid formed isotropic solutions of micelles, whereas the ethanolamine salts of the same acids formed turbid birefringent lamellar solutions. The structure and dimension of those phases were confirmed by small-angle neutron scattering and NMR. Micelles exhibited a surprisingly small radius of about 20 A, even for hydroxyl fatty acids, suggesting the formation of hydrogen bonds between lipids in the core of the micelles. In the case of ethanolamine salts of palmitic and 12-hydroxy stearic acids, the lipids were arranged in bilayers, with a phase transition from gel to fluid upon heating, whereas for omega-hydroxy palmitic acid, monolayers formed in accordance with the bola shape of this lipid. Foams and emulsions produced from ethanolamine salt solutions were more stable than those obtained from tetrabutyl-ammonium salt solutions. We discuss these results in terms of counterion size, lipid molecular shape, and membrane curvature.

Research paper thumbnail of Polysaccharide/Surfactant Complexes at the Air−Water Interface − Effect of the Charge Density on Interfacial and Foaming Behaviors

Langmuir, 2008

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively c... more The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces, was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide.

Research paper thumbnail of The stability mechanisms of an injectable calcium phosphate ceramic suspension

Journal of Materials Science: Materials in Medicine, 2010

Calcium phosphate ceramics are widely used as bone substitutes in dentistry and orthopedic applic... more 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.

Research paper thumbnail of Effect of high pressure homogenisation on methylcellulose as food emulsifier

Journal of Food Engineering, 2003

A new high pressure homogeniser going up to 350 MPa was used to produce fine emulsions stabilised... more 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.

Research paper thumbnail of β-Lactoglobulin aggregates in foam films: Correlation between foam films and foaming properties

Journal of Colloid and Interface Science, 2009

Single foam films made from aqueous protein solutions containing aggregates have been studied usi... more 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.

Research paper thumbnail of Foaming properties of protein/pectin electrostatic complexes and foam structure at nanoscale

Journal of Colloid and Interface Science, 2010

The foaming properties, foaming capacity and foam stability, of soluble complexes of pectin and a... more 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.

Research paper thumbnail of Self-similar assemblies of globular whey proteins at the air–water interface: Effect of the structure

Journal of Colloid and Interface Science, 2010

We investigated the structure of heat-induced assemblies of whey globular proteins using small an... more 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.

Research paper thumbnail of Oleosins of Arabidopsis thaliana :  Expression in Escherichia coli , Purification, and Functional Properties

Journal of Agricultural and Food Chemistry, 2004

The interfacial behavior of oleosins, the most abundant proteins from seeds oil bodies, was inves... more 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 -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 -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.

Research paper thumbnail of Detailed Physicochemical Characterization of the 2S Storage Protein from Rape ( Brassica napus L.)

Journal of Agricultural and Food Chemistry, 2004

Chromatographic, chemical, and spectroscopic techniques were used to characterize the physicochem... more Chromatographic, chemical, and spectroscopic techniques were used to characterize the physicochemical properties of napin purified by preparative chromatography. The molar extinction coefficient was determined ( ) 0.56), and static and dynamic light scattering measurements enabled the average molecular weight (M w ) 13919), the second virial coefficient (A 2 ) 23.95 × 10 -5 mol cm 3 g -2 ), and the hydrodynamic radius (R H ) 1.98 nm) to be determined. No conformational changes were observed by fluorescence and circular dichroism measurements in different buffers at pH 3, 4.6, 7, and 12, confirming the high pH stability of this protein. From MALDI-TOF analysis and after enzymatic digestion, it was found that this purified sample, extracted from the rapeseed variety Express, contained mainly isoform 2SS3_BRANA.

Research paper thumbnail of Chemical characterisation and gelling properties of cell wall polysaccharides from species of Ulva (Ulvales, Chlorophyta)

Research paper thumbnail of Modifications of the charges at the N-terminus of bovine β-casein: Consequences on its structure and its micellisation

Food Hydrocolloids, 2007

Due to the combination of flexibility and amphiphilicity, in solution b-casein (b-CN) acts as a s... more Due to the combination of flexibility and amphiphilicity, in solution b-casein (b-CN) acts as a surfactant molecule. It undergoes selfassociation 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 b-CN in its association behavior. b-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 b-CN has been obtained by heterologous expression in the prokaryotic host Escherichia coli. A mutant (MU A 2 ) form of b-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 b-CN have different behaviors in temperaturedependent 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 b-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 b-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 b-CN, which means that the mutation reinforces monomers interaction at the surface. r

Research paper thumbnail of Degradation of methylcellulose during ultra-high pressure homogenisation

Food Hydrocolloids, 2002

Initially developed for the dairy industry, the very high pressure homogenisation (.100 MPa) is n... more 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 ®ne 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 multiangle laser light scattering and refractive index detection (SEC/MALLS/RI). The strong elongational¯ow encountered by the polymer at the entrance of the valve of the high pressure homogeniser device may bring suf®cient energy to disrupt covalent bonds. Consequently, as shown by¯ow behaviour the thickening properties of this polymer were also reduced. q (J. Floury), desrumau@enitiaa-nantes.fr (A. Desrumaux), axelos@nantes.inra.fr (M.A.V. Axelos), jack.legrand@crttsn.univ-nantes.fr (J. Legrand).

Research paper thumbnail of SEC−MALLS and SANS Studies Applied to Solution Behavior of Linear α-Glucans

Macromolecules, 2000

Both size-exclusion chromatography coupled on-line with multiangle-laser-light-scattering (SEC−MA... more Both size-exclusion chromatography coupled on-line with multiangle-laser-light-scattering (SEC−MALLS) and small-angle neutron scattering (SANS) demonstrate that linear α-glucan chains adopt the conformation of random coils with a higher dimension in alkaline ...

Research paper thumbnail of Effect of galactomannans on the viscoelastic behaviour of pectin/calcium networks

Polymer Gels and Networks, 1996

Research paper thumbnail of Effect of heat treatment, final pH of acidification, and homogenization pressure on the texture properties of cream cheese

Dairy Science & Technology, 2014

Research paper thumbnail of Heavy metals binding by pectins: selectivity, quantification and characterisation

Progress in Biotechnology, 1996

Citrus and sugar-beet pectins with similar degrees of methylation were put in contact with divale... more Citrus and sugar-beet pectins with similar degrees of methylation were put in contact with divalent metal ions in presence of 0.1M NaNO3 or in pure water. pH studies and binding isotherms allowed to establish the same scale of selectivity for both pectins, decreasing as follows: Cu2+∼Pb2+≫Zn2+≥Cd2+∼Ni2+>Ca2+. Binding isotherms showed the same features for both pectins according to the ionic strength,

Research paper thumbnail of Surface and Interfacial Properties of Natural Hydrocolloid Emulsifiers

Research paper thumbnail of Interactions of pectins with multivalent cations: Phase diagrams and structural aspects

Progress in Biotechnology, 1996

... Sci., 13 (1954) 43. 27 JF Joanny and L. Leibler, J. Phys. ... Rev. Lett., 64 (1990) 1457. 35 ... more ... Sci., 13 (1954) 43. 27 JF Joanny and L. Leibler, J. Phys. ... Rev. Lett., 64 (1990) 1457. 35 MAV Axelos, MM Mestdagh, unplubished results 36 S. Cros, C. Garnier, MAV Axelos, A. Imberty, S. Perez, Biopolymers (1996) 37 BA Burton and DA Brant, Biopolymers, 22 (1983) 1769. ...

Research paper thumbnail of In Situ Investigations on Organic Foam Films Using Neutron and Synchrotron Radiation

Langmuir, 2005

We report on small-angle neutron scattering (SANS) and X-ray scattering (SAXS) investigations of ... more We report on small-angle neutron scattering (SANS) and X-ray scattering (SAXS) investigations of foam films stabilized by sodium dodecyl sulfate. Previous measurements on dry foams (Axelos, M. A. V.; Boué, B. Langmuir 2003, 19, 6598) have shown the presence of spikes in the two-dimensional scattering data which suggest that the incident beam is reflected on some film surfaces. The latter interpretation is confirmed by new neutron studies performed on ordered ("bamboo") foams which allow selection of single films. In the first case, we show that the spikes of the scattered intensity can be obtained by reflection on two parts of the foam, namely, the films and the Plateau borders. With synchrotron radiation, first observations of distinct interference fringes have allowed an accurate determination of the film thickness. A comparison with X-ray and neutron data is made, opening a general discussion about the capabilities of small-angle scattering techniques for studying the microscopic properties of foam films.

Research paper thumbnail of Foams As Viewed by Small-Angle Neutron Scattering

Research paper thumbnail of Self-Assembly of Fatty Acids and Hydroxyl Derivative Salts

Langmuir, 2008

We report the dispersions of a fatty acid and hydroxyl derivative salts in aqueous solutions that... more We report the dispersions of a fatty acid and hydroxyl derivative salts in aqueous solutions that were further used to produce foams and emulsions. The tetrabutyl-ammonium salts of palmitic acid, 12-hydroxy stearic acid, and omega-hydroxy palmitic acid formed isotropic solutions of micelles, whereas the ethanolamine salts of the same acids formed turbid birefringent lamellar solutions. The structure and dimension of those phases were confirmed by small-angle neutron scattering and NMR. Micelles exhibited a surprisingly small radius of about 20 A, even for hydroxyl fatty acids, suggesting the formation of hydrogen bonds between lipids in the core of the micelles. In the case of ethanolamine salts of palmitic and 12-hydroxy stearic acids, the lipids were arranged in bilayers, with a phase transition from gel to fluid upon heating, whereas for omega-hydroxy palmitic acid, monolayers formed in accordance with the bola shape of this lipid. Foams and emulsions produced from ethanolamine salt solutions were more stable than those obtained from tetrabutyl-ammonium salt solutions. We discuss these results in terms of counterion size, lipid molecular shape, and membrane curvature.

Research paper thumbnail of Polysaccharide/Surfactant Complexes at the Air−Water Interface − Effect of the Charge Density on Interfacial and Foaming Behaviors

Langmuir, 2008

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively c... more The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces, was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide.

Research paper thumbnail of The stability mechanisms of an injectable calcium phosphate ceramic suspension

Journal of Materials Science: Materials in Medicine, 2010

Calcium phosphate ceramics are widely used as bone substitutes in dentistry and orthopedic applic... more 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.

Research paper thumbnail of Effect of high pressure homogenisation on methylcellulose as food emulsifier

Journal of Food Engineering, 2003

A new high pressure homogeniser going up to 350 MPa was used to produce fine emulsions stabilised... more 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.

Research paper thumbnail of β-Lactoglobulin aggregates in foam films: Correlation between foam films and foaming properties

Journal of Colloid and Interface Science, 2009

Single foam films made from aqueous protein solutions containing aggregates have been studied usi... more 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.

Research paper thumbnail of Foaming properties of protein/pectin electrostatic complexes and foam structure at nanoscale

Journal of Colloid and Interface Science, 2010

The foaming properties, foaming capacity and foam stability, of soluble complexes of pectin and a... more 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.

Research paper thumbnail of Self-similar assemblies of globular whey proteins at the air–water interface: Effect of the structure

Journal of Colloid and Interface Science, 2010

We investigated the structure of heat-induced assemblies of whey globular proteins using small an... more 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.

Research paper thumbnail of Oleosins of Arabidopsis thaliana :  Expression in Escherichia coli , Purification, and Functional Properties

Journal of Agricultural and Food Chemistry, 2004

The interfacial behavior of oleosins, the most abundant proteins from seeds oil bodies, was inves... more 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 -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 -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.

Research paper thumbnail of Detailed Physicochemical Characterization of the 2S Storage Protein from Rape ( Brassica napus L.)

Journal of Agricultural and Food Chemistry, 2004

Chromatographic, chemical, and spectroscopic techniques were used to characterize the physicochem... more Chromatographic, chemical, and spectroscopic techniques were used to characterize the physicochemical properties of napin purified by preparative chromatography. The molar extinction coefficient was determined ( ) 0.56), and static and dynamic light scattering measurements enabled the average molecular weight (M w ) 13919), the second virial coefficient (A 2 ) 23.95 × 10 -5 mol cm 3 g -2 ), and the hydrodynamic radius (R H ) 1.98 nm) to be determined. No conformational changes were observed by fluorescence and circular dichroism measurements in different buffers at pH 3, 4.6, 7, and 12, confirming the high pH stability of this protein. From MALDI-TOF analysis and after enzymatic digestion, it was found that this purified sample, extracted from the rapeseed variety Express, contained mainly isoform 2SS3_BRANA.

Research paper thumbnail of Chemical characterisation and gelling properties of cell wall polysaccharides from species of Ulva (Ulvales, Chlorophyta)

Research paper thumbnail of Modifications of the charges at the N-terminus of bovine β-casein: Consequences on its structure and its micellisation

Food Hydrocolloids, 2007

Due to the combination of flexibility and amphiphilicity, in solution b-casein (b-CN) acts as a s... more Due to the combination of flexibility and amphiphilicity, in solution b-casein (b-CN) acts as a surfactant molecule. It undergoes selfassociation 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 b-CN in its association behavior. b-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 b-CN has been obtained by heterologous expression in the prokaryotic host Escherichia coli. A mutant (MU A 2 ) form of b-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 b-CN have different behaviors in temperaturedependent 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 b-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 b-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 b-CN, which means that the mutation reinforces monomers interaction at the surface. r

Research paper thumbnail of Degradation of methylcellulose during ultra-high pressure homogenisation

Food Hydrocolloids, 2002

Initially developed for the dairy industry, the very high pressure homogenisation (.100 MPa) is n... more 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 ®ne 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 multiangle laser light scattering and refractive index detection (SEC/MALLS/RI). The strong elongational¯ow encountered by the polymer at the entrance of the valve of the high pressure homogeniser device may bring suf®cient energy to disrupt covalent bonds. Consequently, as shown by¯ow behaviour the thickening properties of this polymer were also reduced. q (J. Floury), desrumau@enitiaa-nantes.fr (A. Desrumaux), axelos@nantes.inra.fr (M.A.V. Axelos), jack.legrand@crttsn.univ-nantes.fr (J. Legrand).