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SUMMARYGlobal variations in the propagation of fundamental-mode and overtone surface waves provide unique constraints on the low-frequency source properties and structure of the Earth’s upper mantle, transition zone and mid mantle. We construct a reference data set of multimode dispersion measurements by reconciling large and diverse catalogues of Love-wave (49.65 million) and Rayleigh-wave dispersion (177.66 million) from eight groups worldwide. The reference data set summarizes measurements of dispersion of fundamental-mode surface waves and up to six overtone branches from 44 871 earthquakes recorded on 12 222 globally distributed seismographic stations. Dispersion curves are specified at a set of reference periods between 25 and 250 s to determine propagation-phase anomalies with respect to a reference Earth model. Our procedures for reconciling data sets include: (1) controlling quality and salvaging missing metadata; (2) identifying discrepant measurements and reasons for discrepancies; (3) equalizing geographic coverage by constructing summary rays for travel-time observations and (4) constructing phase velocity maps at various wavelengths with combination of data types to evaluate inter-dataset consistency. We retrieved missing station and earthquake metadata in several legacy compilations and codified scalable formats to facilitate reproducibility, easy storage and fast input/output on high-performance-computing systems. Outliers can be attributed to cycle skipping, station polarity issues or overtone interference at specific epicentral distances. By assessing inter-dataset consistency across similar paths, we empirically quantified uncertainties in traveltime measurements. More than 95 per cent measurements of fundamental-mode dispersion are internally consistent, but agreement deteriorates for overtones especially branches 5 and 6. Systematic discrepancies between raw phase anomalies from various techniques can be attributed to discrepant theoretical approximations, reference Earth models and processing schemes. Phase-velocity variations yielded by the inversion of the summary data set are highly correlated (R ≥ 0.8) with those from the quality-controlled contributing data sets. Long-wavelength variations in fundamental-mode dispersion (50–100 s) are largely independent of the measurement technique with high correlations extending up to degree ∼25. Agreement degrades with increasing branch number and period; highly correlated structure is found only up to degree ∼10 at longer periods (T > 150 s) and up to degree ∼8 for overtones. Only 2ζ azimuthal variations in phase velocity of fundamental-mode Rayleigh waves were required by the reference data set; maps of 2ζ azimuthal variations are highly consistent between catalogues ( R = 0.6–0.8). Reference data with uncertainties are useful for improving existing measurement techniques, validating models of interior structure, calculating teleseismic data corrections in local or multiscale investigations and developing a 3-D reference Earth model.

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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.

The effect of Cassia gum galactomannan on the thermal gelation of a whey protein isolate (WPI) at 80 °C has been monitored by rheological dynamic measurements at fixed frequency and the mechanical spectra of the gels have been recorded at 80 °C and after quenching to 20 °C. The mechanical spectra were analysed quantitatively by fitting a Cole–Cole model to the storage and loss compliance versus frequency data. The concentration of WPI was 110 g/l and that of Cassia gum varied from 0 to 11 g/l. At low concentration, the presence of the galactomannan enhanced the aggregation rate and the strength of the protein gel but did not modify intrinsically the gelation process and the structure of the system. At higher galactomannan concentrations, the gels displayed substantially lower moduli values and the shape of the mechanical spectra was modified. This was tentatively interpreted as the consequence of a depletion-induced liquid–liquid phase separation occurring during the course of the aggregation process, responsible for the downturn observed on the loss modulus versus time curves monitored at 80 °C.

This study reports an observation of submicrometer multilamellar vesicles (MLVs) prepared by simply freeze-thawing a phospholipid dispersion at full hydration that transformed into giant vesicles (GVs) and tubules (TUs) when confined between microscope glass slides. Cover slide cleaning and surface treatment did not hamper the formation of GVs or TUs. However, when small unilamellar vesicles (SUV) were prepared or when MLVs were not confined but rather freely moved between the glass slides or when the phospholipid was in its gel phase, neither GVs nor TUs were observed. Altogether, our results suggested that MLVs would play a role as a lipid reservoir and that the liquid flow between the glass slides induces the peeling of the external bilayers, yielding the formation of tubules and giant unilamellar vesicles.

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.

A new and efficient method for the preparation in one step of water-soluble cellulose acetate sulfate derivatives (CAS) is reported. Acetylation and sulfation were carried out simultaneously, using a mixture of acetic anhydride and sulfuric acid in glacial acetic acid. The reaction time and the amount of acetic anhydride were optimized and the method provided water-soluble esters, with a degree of acetylation in the range 1.6 and 2.4 and a degree of sulfation of 0.3. This method has been successfully applied to pure cellulose and to cellulose-enriched materials obtained from agricultural by-products. The product exhibited a high viscosity in aqueous solution suggesting interesting rheological properties.

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.

The EPS produced by Propionibacterium acidi-propionici DSM 4900 has been investigated on a biochemical and a rheological basis. The EPS was mainly composed of galactose, mannose, and glucosamine, with traces of glucose, galactosamine and phosphate. It could be fractionated by anion-exchange chromatography into a major (78%) acidic fraction and a minor neutral component. Viscosity determinations in the absence and presence of salt showed a polyelectrolyte behavior and an intrinsic viscosity of 22 dl/g in 0.01 M NaCl. EPS solutions displayed a shear-thinning behavior with limiting zero-shear viscosity (η0). Variations of the specific limiting viscosity (ηsp0) as a function of concentration indicated three concentration regimes with c ∗ =0.2 and c ∗∗ =2 g / l . At relatively low concentration (4–18 g/l), G′ and G″ showed variations with limiting slopes of 2 and 1, respectively, at low frequency and a crossover of these two moduli at high frequency. Master curves of the flow curves as well as of the viscoelastic functions could be built. At the lowest concentrations, the Cox–Merz rule was obeyed while at the highest ones the superposition of |η ∗ (ω)| and η( γ ) curves was obtained only at low frequencies. All these rheological determinations show that aqueous solutions of EPS behave as entangled polymer solutions. The polysaccharide does not display gelling properties and could be used as a highly viscous thickener.

International audience; Mutagenesis experiments suggest that Asp79 in cellulase Cel6A (E2) from Thermobifida fusca has a catalytic role, in spite of the fact that this residue is more than 13 Å from the scissile bond in models of the enzyme–substrate complex built upon the crystal structure of the protein. This suggests that there is a substantial conformational shift in the protein upon substrate binding. Molecular mechanics simulations were used to investigate possible alternate conformations of the protein bound to a tetrasaccharide substrate, primarily involving shifts of the loop containing Asp79, and to model the role of water in the active site complex for both the native conformation and alternative low-energy conformations. Several alternative conformations of reasonable energy have been identified, including one in which the overall energy of the enzyme–substrate complex in solution is lower than that of the conformation in the crystal structure. This conformation was found to be stable in molecular dynamics simulations with a cellotetraose substrate and water. In simulations of the substrate complexed with the native protein conformation, the sugar ring in the –1 binding site was observed to make a spontaneous transition from the 4C1 conformation to a twist-boat conformer, consistent with generally accepted glycosidase mechanisms. Also, from these simulations Tyr73 and Arg78 were found to have important roles in the active site. Based on the results of these various MD simulations, a new catalytic mechanism is proposed. Using this mechanism, predictions about the effects of changes in Arg78 were made which were confirmed by site-directed mutagenesis.

In food matrices, where starch is often used as a gelling or texturing agent, the occurrence of amylose-aroma complexes and their effect on the release of aroma compounds are difficult to determine. Indeed, thick or gelled systems are known to reduce the diffusion rate of flavor molecules, resulting in an increase of retention. Moreover, interactions between aroma compounds and matrix components might increase the retention of aroma compounds. The complexing behavior of three aroma compounds with amylose was studied by DSC and X-ray diffraction to determine the relative importance of these two factors. Their interaction properties were different: two of them formed complexes, and the third did not. These aroma compounds were added in food matrices containing different starches that induced different textures. Their retention was studied by static headspace analysis. The retention of aroma compounds appeared to depend on the amylose/amylopectin ratio of starch, both from the formation of complexes and by a viscosity effect.

The structure of acacia gum molecules was determined using size exclusion chromatography coupled to multi-angle laser light scattering, refractometry and viscosimetry. Results revealed the presence of many molecular species, including large aggregates, the arabino-galactan protein fraction (AraGP), the arabino-galactan fraction (AraG) and the glyco-protein fraction (GP). The M w of the two major fractions AraGP and AraG were 2.3 10 6 and 2.7 10 5 g mol −1 , respectively. The [ η ], R g and R h of the acacia gum sample were 0.23 dl g −1 , 14.2 and 11.9 nm, respectively. From the determination of R g / R h ratio (1.2) or the exponent ν (0.55) of the power-law relationship between R g and M w , it was tentatively suggested that acacia gum molecules displayed a random coil shape. Flow behaviour and viscoelastic properties of acacia gum dispersions at pH 4.2 were determined using shear-controlled rheometers with cone-plate or coaxial cylinders measuring systems. Acacia gum dispersions at concentrations between 3 and 32 wt% showed shear-thinning flow behaviour at shear rates −1 . Time-dependent thickening flow behaviour was also demonstrated on 3 wt % acacia gum dispersions at shear rates −1 . The effect almost vanished at gum concentrations≥20 wt% but increased adding dodecan onto samples to prevent dehydration. The η a of acacia gum dispersions increased after ageing in the measuring devices and a stress overshoot was noticed during the measurement of η a . Acacia gum dispersions displayed structured liquid viscoelastic properties with a slope in the log–log plot of G′ and G″= f (frequency) traces equal to 1.4 and 0.8, respectively. After ageing, dispersions displayed solid-like mechanical properties with G′ above G″ over the entire range of frequencies selected. These unusual results were thought to be due to the known surface properties of acacia gum molecules, especially to the ability of the gum to form elastic films at air/water or oil/water interfaces. These features were confirmed using a dynamic drop tensiometer by measuring during 1 h the interfacial dilational modulus |ϵ| at air/water or dodecan/water interface. Our results indicated that an interplay could exist between bulk and surface rheological properties of acacia gum dispersions. Whether such a trend is only a characteristic of acacia gum or could be generalized to other surface active molecules remains to be studied.

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.

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.

X-ray crystallinity of amylose and amylopectin films with 0, 10 and 30% of glycerol and stored at RH 0, 54 and 91% were studied. Films prepared of water cast dilute solutions and dried at 70°C were thin and transparent. Each fresh amylose film showed B-type crystalline structures, and depending on the glycerol and water contents the amount of crystallinity varied from 6 to 32%. No changes in the crystallinity of the amylose films were observed during storage of two months. The fresh amylopectin films were completely amorphous. After storage for two months at the highest humidity the amylopectin film with 30% glycerol showed crystalline structure (19%), but all other amylopectin films remained amorphous during ageing. The crystal formation in the highly plasticised amylopectin film was suggested to be due to its rubbery state under the storage conditions. Amylose films were stable in water unlike amylopectin films that dispersed fast in water. About 35% of the amylose films were resistant to α-amylase, whereas amylopectin films were hydrolysed wholly. Also when treated with hydrochloric acid the amylopectin films dissolved totally and fast, while one week was needed to dissolve about 50% of the amylose films. It was concluded that even if part of the amylose films were amorphous, also these amorphous regions were more resistant to hydrolysis than the amorphous amylopectin structures.

Secondary structural changes of glycinin during film and gel formation were studied by infrared spectroscopy. Two complementary data treatments—i.e., principal component analysis and two-dimensional correlation spectroscopy—were applied to the infrared spectra in order to determine the time evolution of conformational changes. Kinetic curves, assessed by taking scores of the first principal components into account, revealed more pronounced changes in the case of film formation. The development of aggregates in film and gel, through intermolecular β-sheets, was identified by an increase of the absorbance band at around 1620 cm−1. Two-dimensional infrared correlation spectroscopy made it possible to observe a decrease in both α-helices and disordered structures prior to the appearance of aggregates. Changes in intramolecular β-sheets took place in a second step. The more drastic changes observed in the case of film formation were believed to result from dehydration and aggregation coupled phenomena.

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.

Cellulose-enriched residues from wheat bran can be transformed in bioplastics after esterification of the cellulose by lauroyl chloride. Before the esterification reaction, an activation step with a swelling of the sample in dilute acid and subsequent drying was required. This activation had a marked influence on the amount of esterified product and its degree of substitution. Using pure cellulose as well as cellulose-enriched agricultural residues, we have shown that the cellulose was totally recovered after this pretreatment and that partial hydrolysis of cellulose chains occurred during the drying step, which probably improved the accessibility to chemical reagents. The possible role of sulfuric acid as catalyst for the esterification reaction of the cellulose by lauroyl chloride was discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1933–1940, 1999

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.

Microparticulated whey proteins (MWP) in suspension or included in a globular protein network revealed that the degree of flocculation was important in the final structure of the material. The MWP dispersions developed an antithixotropic character when low shear rate was applied to the system even at low temperature. Similar results were obtained on globular protein solutions and could be interpreted in terms of an orthokinetic aggregation. MWP participated to the formation and reinforcement of heat-induced β -lactoglobulin (BLG) gels. The mechanical properties of mixed gels demonstrated synergestic effects at low MWP massic fraction (BLG:MWP ratio higher than 2:1). A possible interpretation would be that both interaction of MWP with the network and flocculation of the MWP inside the pores could occur. However, increasing the fraction of MWP induced heterogeneities in the protein network. In particular, micro-phase separation due to steric hindrance effects or thermodynamic incompatibility between the two components could occur and decrease viscoelastic properties of mixed gels.

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.

Starches of four types, from maize (normal, or chemically modified, waxy), wheat (unmodified) and rice (waxy, unmodified), have been investigated under different pasting conditions. The effect of the upper pasting temperature which is known to be of particular importance in the functional properties of starch in industrial processes has been specifically investigated. The rheological properties have been assessed from viscosity measurements (flow behaviour) at 60 °C. Gel properties upon cooling the paste were estimated through viscoelastic measurements in oscillatory shear. The main objective was to evaluate the effect of thermal treatment on the textural characteristics of a bechamel sauce, taken as a model of starch-based sauces, and prepared with the same starches in similar pasting conditions. Overall, the differences noticed in the flow and viscoelastic properties of the different starches were also found in the bechamel sauces formulated with the same starches.

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.

Sorption behaviour and calorimetric glass transition were measured on cast starch films plasticized with varying concentrations of different components (glycerol, sorbitol, lactic acid sodium, urea, ethylene glycol, diethylene glycol, PEG 200, glycerol diacetate). Precision analysis showed that the water level in samples conditioned at 57% relative humidity reached a minimum for a plasticizer content of 10–20% (dry basis). Starting from 14.8% of water (dry basis) as measured in the amorphous starch-water system, a minimum of 12.7 to 14.4% can be attained according to the type of plasticizer added. Glass transition, as determined on samples conditioned at a constant relative humidity (57%), depended on the type of plasticizer used, although general behaviour was broadly similar for all components except glycerol diacetate. Casting trials performed with this substance revealed an evident phase separation and Tg of starch did not appear really modified by its presence. For glycerol, sorbitol and lactic acid sodium, glass transition was measured with respect to plasticizer and water content. Couchman's relation was applied, which describes the Tg variation of the monophasic polymer—diluant system. The likelihood of phase separation for a high plasticizer level is considered.

Order-disorder transitions were investigated in native cassava starch at intermediate moisture contents (35 to 60% wt. water), using Differential Scanning Calorimetry (DSC) and dynamic Wide Angle X-ray Diffractometry (WAXS) with a synchrotron radiation source.

Five amylose preparations of different origins (cassava, potato, smooth seeded pea, wheat and maize), obtained from native starch granules by thymol complexation, were ultracentrifuged as the final decontamination step to remove a high molecular weight population contaminating the amylose solutions. The efficiency of this ultracentrifugation procedure was assessed by dynamic light scattering (DLS): decreases in apparent hydrodynamic radii, R? H , from 46·1–72·6 nm before ultracentrifugation to 16·1–29·3 nm after were observed. Amylose solutions were then characterised by size exclusion chromatography coupled on-line to multi-angle laser light scattering (SEC–MALLS). Under these conditions M? w of cassava, potato, smooth seeded pea, wheat and maize amyloses were, respectively, 1·05×10 6 , 7×10 5 , 6·2×10 5 , 5·1×10 5 and 3·4×10 5 g/mol. Using a specific optimisation algorithm, experimental molecular weight distributions (MWD) were fitted by two mathematical models of ‘Most Probable’ distribution and ‘log-normal’ distribution. The best fit was obtained for the second model, but fitted M? w were higher than experimental M? w . When a ‘Most Probable’ model was used, the fitted M? w were consistent with experimental M? w but with a lower quality of fit. Exponents c in the power law R G = KM c were between 0·6 and 0·7, indicating an extended linear random coil in the range of MW analysed (3×10 5 –9×10 6 g/mol). This procedure was also applied to the characterisation of different commercial amylose products.

Une etude de la structure par diffusion des neutrons aux petits angles et de la rheologie de solutions natives et de gels de β-lactoglobuline a pH 9 et faible force ionique a ete realisee. Les proprietes rheologiques des solutions se caracterisent par un comportement antithixotrope et viscoelastique. Dans le cas des agregats et des gels obtenus apres traitement thermique, un pic de correlation est observe qui varie comme C 0,5 . Il decroit avec l'augmentation de la force ionique. La dilution des agregats entraine la perte des correlations et met en evidence une structure interne des agregats identique a celle des gels. Les gels a faible force ionique manifestent un comportement viscoelastique de type liquide. A forte force ionique, les agregats presenteraient des structures auto-similaires entre 400 et 40 A, les dimensions fractales mesurees sont de 1,3 a faible concentration et 1,75 a plus forte concentration. Cette dimension fractale est inchangee apres dilution des agregats formes en milieu concentre.

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.

International audience; The gelation process of two polysaccharides, amy lose and alginate, has been investigated by means of ultrasonic spectroscopy. This method allows an immediate analysis of the acoustic wave propagating through the medium by means of Fast Fourier Transform of the signals. Measurements were performed within the frequency range 15–100 MHz. The absorption and the velocity of the ultrasonic wave can therefore be obtained as a function of time over a given frequency range. The results were compared to classical rheological measurements in oscillatory shear at a low strain amplitude and, in case of amylose, to turbidity variations. In the course of amy lose gelation, variations in the absorption of the ultrasonic signal paralleled those of turbidity in the medium and took place at a much earlier stage than the one at which the increase in G′ and G″ can be detected. In the case of alginate, absorption variations paralleled more closely those of the viscoelastic parameters G′ and G″. The differences can be interpreted in relation to the mechanisms of gelation. Amylose gelation takes place through a phase separation. Ultrasound appears extremely sensitive to such changes in the material. The method shows the first steps in the phase separation phenomenon. This suggests that variations in the ultrasonic absorption can be taken as a means to detect the earlier steps of the gelation process of starchy materials. Gelation of alginate is a calcium-mediated process, in which case, ultrasounds provide similar information as rheological measurements.

Wheat flours differing in their lipid and non-prolamin protein (NPP) contents were obtained by chloroform or Lubrol PX extraction. Starch was hand-washed out of the flour, and the resulting glutens were studied by dynamic rheology and electron spin resonance spectroscopy (ESR) spin probing and spin labeling. Compared to control gluten, the storage modulus of NPP-including lipoprotein-depleted gluten is unchanged, and the loss modulus is not significantly different. The mobility of spin probes differing in size in the gluten aqueous phase suggests the existence of at least two compartments : a network with a mesh size of about 0.8 nm and larger water pockets. These compartments are present in all glutens. The spectra resulting from ESR spin labeling experiments are composite, reflecting the contribution of at least two types of polypeptides differing in flexibility. The population of mobile spin labels linked to the lysine residues is much larger in control gluten compared to NPP depleted gluten, indicating the lysine residues of these proteins are in a less flexible environment. On the contrary, only a slight difference is observed between the various samples when cysteine residues are labeled. These results suggest that NPP and lipids behave only as fillers in the prolamin network.

Vh-type crystals were prepared by precipitation in pure alcohol of amylose solutions in dimethyl sulfoxide (DMSO). The respective influences of amylose chain length and final equilibrium relative humidity (E.R.H.) on the nature of transitions induced by moisture exchanges were studied extensively using X-ray diffraction. The nature and kinetics of observed transitions depend on amylose chain length. If the Va form is always observed upon dehydration, A, B or mixtures of A and B forms are obtained according to the amylose chain length when rehydrating over higher water activities. Other specific transitions occurred when the Vh material was preliminary crystallized in mixture of ethanol and water (80/20,v/v). Some results suggest that these transitions occur through a transient disappearance of crystallinity and subsequent reorganization. Such mechanisms would be more conceivable than a solid state conversion from a single helical conformation (Vh type) to a double one (A and B types). Polymorphe, durch Feuchtigkeitsaustausch induzierte Ubergange von Amylose-Ethanol-Kristallkomplexen. Durch Fallung in reinem Alkohol von Losungen von Amylose in Dimethylsulfoxid (DMSO) wurden Kristalle des Vh-Typs dargestellt. Die besonderen Einflusse der Amylosekettenlange und der abschliesenden Gleichgewichts-Relativ-Feuchtigkeit (E.R.H.) der durch Feuchtigkeitsaustausch induzierten Ubergange wurden unter Verwendung der Rontgenbeugung umfassend untersucht. Die Art und die Kinetik der beobachteten Ubergange sind von der Amylosenkettenlange abhangig. Wenn die Va-Form immer nach der Dehydrierung beobachtet wird, werden A, B oder Mischungen aus A-und B-Form erhalten entsprechend der Amylosekettenlange, wenn sie uber hohere Wasseraktivitaten rehydratisiert werden. Andere spezifische Ubergange treten auf, wenn das Vh-Material zuvor in einer Mischung aus Ethanol und Wasser (80/20, v/v) kristallisiert worden war. Einige Erlebnisse lassen vermuten, das diese Ubergange durch ein vorubergehendes Verschwinden der Kristallinitat mit nachfolgender Reorganisation auftreten. Derartige Mechanismen waren eher denkbar als eine Konversion im festen Zustand von einer einzigen helikalen Konformation (Vh-Typ) in eine doppelte A- und B-Typen).

We present a rheological study of the gel transition in silica gels resulting from the hydrolysis condensation of a silicon alkoxide. The complex shear modulus is measured in a large frequency range (10 -2 -10 2 rad/s). The exponents for the viscosity s=0.7±0.1, for the elasticity t=2.0±0.1, for the dynamic crossover frequency z=2.9±0.2, and for the scaling-frequency power law Δ=0.72±0.03 are in agreement with the scalar percolation model in a restricted region around the gelation time (3%). Beyond, there is a crossover to a vectorial percolation regime characterized by a much higher elasticity exponent t'=3.6±0.1

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 flux and crystallization are major problems for cryopreservation. The gel approach relies on the concept that a biological gel network might sufficiently entrap fluid within its pores, so as to maintain it osmotically inactive under the stresses usually encountered in the course of cryopreservation and limit the extent of crystallization. It could even induce vitrification. The effects of some cryosolvents on the structure of denatured collagen gels were studied as a function of temperature by hydraulic conductivity measurements and electron microscopy observations, so as to explore the porosity and fluid behavior of the gels. Gels formed in the presence of methanol exhibit a large increase in pore size as gelation temperature drops, whereas almost no variation is detected with ethylene glycol, where the porosity is finer. Gels in the presence of ethylene glycol display a larger fluid content, smaller flow rates, and better pressure resistance than those in the presence of methanol. Electron micrographs confirm the variations in gel structures depending on the cryosolvent and the temperature. Rheological measurements also support these observations. Upon rapid cooling, vitrification occurs only in gels with ethylene glycol. Ethylene glycol seems to have a specific interaction with denatured collagen gels which induces a finer network better adapted for trapping fluid osmotically inactive in the course of cryopreservation.

The aim of this work was to study the structural features of aqueous starch gels as a function of their amylose:amylopectin ratio, r . Structural characteristics of amylose-amylopectin gels were studied using uniaxial compression measurements, mild acid hydrolysis, α-amylolysis, X-ray diffractometry and hot water solubility. Two families of gels were isolated according to the amylose:amylopectin ratio ( r ). Mixed gels had similar behaviour either to pure amylopectin gels for r r . Amylopectin-rich gels were fairly well degraded both chemically (60 to 100%) and enzymically (∼ 50%), but had poor mechanical properties and solubility behaviour. Amylose-rich gels however were slightly degraded (∼ 20% in all cases), but exhibited good mechanical and thermal resistances. Results were explained in terms of supra-molecular organization, suggesting a phase-separated structure with a continuous matrix of one polymer embedding microdomains of the second polymer. Polymer composition of each phase was determined by the ratio r , and the particular value of r = 0·43 was interpreted as the inversion point between the two types of gel.

Single crystals of amylose complexed with isopropanol or acetone were prepared by adding these precipitants to a metastable aqueous solution of amylose. With both precipitants, similar micrometre sized platelet crystals were obtained. They gave indistinguishable electron diffraction diagrams which could be indexed in an orthorhombic unit cell, with a = 28.26 A, b = 29.30 A, c = 8.01 A and in a space group P2(1)2(1)2(1) or P2(1)2(1)2. Within the unit cell, the amylose chains are organized in antiparallel pairs of parallel 6(5) amylose helices occupying 70% of the cell content, the remaining 30% consisting of isopropanol/acetone and water, with an estimate of 10 isopropanol/acetone molecules for 52 water molecules per unit cell. If the crystals are suspended in pure isopropanol at various temperatures or in pure methanol at room temperature, they undergo a de-solvation process that ultimately converts them into VH amylose. De-solvation with isopropanol left the crystals intact whereas with methanol, they became cracked during the shrinkage. An explanation is proposed for such difference.

The apparent viscosity of three test meals containing 6% of different guar gums was measured in the gastric, duodenal and jejunal contents and related with the gastrointestinal myoelectric activity and transit time in pigs. The motility index (mV/min) and the spike burst frequency (number of spike bursts/min) were closely related to the digesta viscosity: they were significantly increased by most viscous contents in stomach and small intestine. This effect was associated with an increase in the orocecal transit time of liquids and solids.

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.

Amylose is known to dissolve in water at temperatures above 130°C. The literature unanimously reports that, provided the polymer content exceeds about 1%, any solution will form a gel upon cooling. The phenomenon is attributed to liquid-liquid phase separation followed by crystallization. In the present work, gels were prepared using carefully controlled thermal histories in sealed glass tubes. The crucial parameter is the dissolution temperature T d , i.e., the maximum temperature at which the solution was heated. If T d

chap. 11; National audience

We present results of a small-angle neutron scattering (SANS) study of a globular protein mixed with a neutral (or charged) polysaccharide, and discuss how the structure is affected by shear. According to SANS measurements, the structures of these mixtures located in the one-phase region of the phase diagram were heterogeneous, the level of flocculated particles being greatly dependent on the polysaccharide and the solvent conditions used. Shearing these types of solutions at low shear rates induced a disruption of the liquid-like short-range order (when it existed) between proteins and a slight anisotropy of the particles indicative of some preferential alignment of proteins in the direction of flow.

Crystalline amylose complexes were prepared with decanal, 1-butanol, menthone and alpha-naphtol. Their crystalline structure and the related helical conformation, determined by wide angle X-ray diffraction (WAXD) and 13C CPMAS solid state NMR, were assigned to V6I, V6II, V6III and V8 types, respectively. It was possible to propose some hypotheses on the possible nature of interactions and especially intra-/inter-helical inclusion. Some shifts in the NMR C1 carbon signals were attributed to the presence of ligand in specific sites inside the structure for a same type of V6 helical conformation. Moreover, the crystallinity and polymorphic changes induced by desorption/rehydration were studied. A general increase of the carbon resonances sharpness upon rehydration has been observed, but also a V6II-V6I transition when decreasing the water content. Differential scanning calorimetry (DSC) experiments were also performed to approach the thermostability of the four types of complex and also the way they form again after melting/cooling sequences.

"Mealiness" is a frequent texture defect in tomato. Currently, this sensory descriptor is not measured by instruments, and it is often described as the result of a defect in the adhesion and rigidity of the cell walls. We have sought to identify the characteristics linked to "mealiness" based on two tomato cultivars (Cameron and Quest), which were collected over several weeks during the production period. The present study used measurement of the compression force during the mechanical destructuring of the pericarps, characterisation through image analysis of the particles generated by crushing, characterisation of the composition and the chemical structure of preparations enriched in cell walls using chemical and biochemical methods, as well as mid-infrared and NMR spectroscopy., défaut de texture fréquemment rencontré dans les fruits. Ce descripteur sensoriel n’est actuellement pas mesuré par des méthodes instrumentales et il est souvent décrit comme résultant d’un défaut d’adhésion et de rigidité des parois cellulaires. Des caractéristiques liées à la « farinosité » ont été recherchées à partir de deux variétés de tomate (Cameron, Quest ) collectées sur plusieurs semaines pendant leur période de production. Ces travaux ont fait appel à la mesure de force de compression lors de la déstructuration mécanique des péricarpes, à la caractérisation par analyse d’image des particules générées par le broyage, à la caractérisation de la composition et de la structure chimique de préparations enrichies en parois par des méthodes chimiques et biochimiques ainsi que par la spectroscopie moyen infrarouge et RMN.

Mealiness, mechanical breakdown and cell wall chemical structure of a mealy (cv ‘Cameron’) and a juicy (cv ‘Quest’) tomato ( Lycopersicon esculentum Mill.) variety were studied over several weeks during the harvest period. A set-up was designed to break tomato pericarp tissue while measuring the rupture energy. For ‘Cameron’, the rupture energy was high and decreased over the harvest period. For ‘Quest’, the rupture energy was low and did not vary throughout the study. The particles in the pulp after breakdown were characterized by image analysis. For ‘Cameron’, intact cells were always recovered from the pulp. Many cell fragments were obtained in the case of ‘Quest’. At the end of the harvest period, ‘Quest’ had a higher content of intact cells. The chemical composition and structure of cell walls in pericarp tissue were determined by biochemical analysis, mid-infrared and solid-state NMR spectroscopy. Cell walls of ‘Cameron’ pericarp tissue were richer in neutral sugars and uronic acid than those of ‘Quest’. The pectin content of ‘Cameron’ samples decreased over the harvest week and was compensated for by protein. ‘Quest’ was richer in mobile arabinan pectic side-chains than ‘Cameron’. Mealiness was correlated with rupture energy, size of recovered particles and mid-infrared data. The data are discussed with regard to cell adhesion and rigidity.

The structure of heat-set systems of the globular protein bovine serum albumin (BSA) was investigated at pH 7 in different salt conditions (NaCl or CaCl(2)) using light scattering. Cross-correlation dynamic light scattering was used to correct for multiple scattering from turbid samples. After heat treatment, aggregates are formed whose size increases as the protein concentration increases. Beyond a critical concentration that decreases with increasing salt concentration, gels are formed. The heterogeneity and the reduced turbidity of the gels were found to increase with increasing salt concentration and to decrease with increasing protein concentration. The structure of the gels is determined by the strength of the repulsive electrostatic interactions between the aggregated proteins. The results obtained in NaCl are similar to those reported in previous studies for other globular proteins. CaCl(2) was found to be much more efficient in reducing electrostatic interactions than NaCl at the same ionic strength.

Heat-induced gelation of globular protein (bovine serum albumin (BSA) and β-Lactoglobulin) mixed with low methoxyl pectin (LM pectin) was studied by rheology and confocal laser scanning microscopy coupled with texture image analysis using the co-occurrence method. Properties of individual biopolymers were also described. The difference between the two globular proteins in the mixture was also evaluated. The structure of BSA gels, characterized by light scattering, depended strongly on NaCl or CaCl₂ content. In the mixture, a competition between protein gelation and phase separation kinetics was evidenced. The control of the kinetics depends on intrinsic and extrinsic factors and especially on the nature and content of added salt. Increasing LM pectin concentration results in a more pronounced phase separation. Depending on biopolymer concentrations and the nature of salt in the medium, protein gels is weakened or strengthened by the presence of the polysaccharide. In presence of calcium, both biopolymers have a specific affinity for this cation that is traduced, for LM pectin, by its ability to form a gel. In the mixture, a composite gel is formed. Depending on NaCl content, gelation of the system is governed either by protein or LM pectin gelation. From all the results obtained, a schematic interpretation of mechanism implied in the formation of mixed gels during the heating process was proposed based on phase separation and gelation of biopolymers.; La gélification thermique de protéines globulaires (albumine de sérum bovin (SAB) et β-Lactoglobuline) en mélange avec la pectine faiblement méthylée (pectine LM) a été étudiée par rhéologie et microscopie confocale à balayage laser couplée à une analyse d'image par la méthode de co-occurrences. Les propriétés des biopolymères seuls ont également été décrites. La différence entre le comportement des deux protéines globulaires en mélange a également été étudiée. La structure des gels de SAB, caractérisée par diffusion de la lumière, varie fortement selon la teneur en NaCl ou CaCl₂. Dans les mélanges, une compétition entre les cinétiques de gélification protéique et de séparation de phase est observée. Celle-ci est fortement dépendante des facteurs intrinsèques et extrinsèques du système, et en particulier de la teneur et la nature des sels ajoutés (NaCl et/ou CaCl₂). L'augmentation de concentration en pectine se traduit par une séparation de phase plus marquée. Selon les conditions de concentrations en biopolymères et la nature des sels dans le milieu, le gel de protéine est affaibli ou renforcé par la présence du polyoside. En présence de calcium, les deux biopolymères présentent une affinité spécifique pour ce cation qui se traduit, pour les pectines LM, par leur capacité à gélifier. En mélange, un gel composite est alors formé. Selon la teneur en NaCl, la gélification du mélange est gouvernée par celle des protéines ou celle des pectines LM. L'ensemble des résultats permet de proposer un schéma d'interprétation des mécanismes impliqués dans la formation des gels en mélange au cours du processus thermique basée sur la séparation de phase et la gélification des biopolymères.