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Background This literature review describes the evolution during baking of the three main components in dough (starch, proteins, and the aqueous phase) in order to understand what causes gas cells to open. To date, most of the literature has focused on the role played by proteins, gluten having received most attention in the last decades (strain hardening properties, ability to stretch without rupturing etc.). The possible role of a liquid lamella has more recently been proposed. While a number of articles directly evidence its existence, indirect results also provide proof of its presence. The role of starch in the mechanisms of gas cell stabilization/destabilization has been little considered. The multiple actions of starch described in this review may offer an explanation for this. Scope and approach The authors have set out to consider all phases and to understand how they may interact during baking in such a way as to lead eventually to gas cell wall rupture. Key findings and conclusions The four most likely situations are presented and discussed: • gluten with poor ability to stretch: rupture occurs too early during baking. • gluten with poor ability to stretch but assisted by a liquid lamella: rupture is delayed; extent of delay is dependent on starch's sorption of water. • gluten with good ability to stretch, starch granules soften early during baking but do not fuse (ideal situation): structure opens late in baking when loaf is able to sustain its own weight. • too many fusing starch granules: gas cell walls fail to rupture and loaf shrinks during cooling.

This review deals with the use of Nuclear Magnetic Resonance techniques to monitor the behavior of starch as well as the migration and distribution of water during the processing or storage of starchy matrices. The aim is to emphasize the potentials of NMR techniques for the quantitative characterization of water transfers in starch-water systems on different length scales. Relaxation and self-diffusion experiments using low-field NMR spectrometry provided important information on the relationship between water dynamics and the microscopic organization of starch granules at various temperatures and water contents. Some works dealt with the botanical origin of starch but also the impact of possible additives. Indeed, the investigation on model starch-based systems was recently expanded to more complex real systems, including dough, bread, cakes, spaghetti and lasagna. Two-dimensional (2D) cross correlation methods have also been developed to elucidate chemical and diffusional proton exchange phenomena, and to improve the interpretation of results obtained in 1D. Finally, magnetic resonance micro-imaging methods were developed to study or to quantify water intake into starch-based matrices.

The effects of starch origin on water migration and starch transformation were investigated using one- and two-dimensional Time-domain NMR (TD-NMR) methods. The quantification of T1 and especially of T2 relaxation times during thermal treatment enabled their interpretation relative to the sorption, gelatinization and retrogradation phenomena of starches in the presence of water, in a level close to that used for bread making (50%, wet basis). Comparison between native wheat, waxy corn and potato starches made possible to link relaxation variations to starch structure and properties as crystallinity, granule size, polymorphism, amylopectin content and water-binding capacity all along heating, cooling and storage processes.

International audience; This research aimed to study the effects of using a partial vacuum for bread baking on macromolecules and water distribution in gluten-free bread. Bread baking under partial vacuum results in greater oven rise and a larger gas fraction in the crumb. Because water's boiling point decreases under reduced pressure, it was expected that its distribution within the dough and its interactions with the others dough's constituents (mainly starch) would differ from those in bread baked under atmospheric pressure. Time-domain nuclear magnetic resonance was used, as it has the rare capacity to quantify both gelatinization and retrogradation of starch. Complementary rheological measurements made it possible to show that crumb Young's modulus was mostly influenced by the gas fraction whereas there was little change in starch gelatinization and retrogradation when dough was baked under partial vacuum. When insufficiently hydrated (48%), the volume of breads was practically the same whatever the baking process. Meanwhile, the nuclear magnetic resonance results suggested that amylose short-term crystallization (on cooling) is dependent on water content. In addition, crumb Young's modulus during storage at room temperature correlated with an increase in free induction decay signal intensity. © 2019 John Wiley & Sons, Ltd.

International audience; The behavior upon immersion in water of two types of starchy materials of biomedical relevance, amorphous potato starch and glycerol-plasticized potato starch, is analyzed in depth. Synchrotron X-ray scattering, specifically wide-angle X-ray scattering (WAXS), and magnetic resonance microimaging (MRμI) are used as very precise and nondestructive quantitative methods to monitor water transfers and structure changes in the samples, with refined spatial and kinetics results. The ingress of water in the cylinder-shaped samples can be inferred from both techniques, and from this, a diffusion mechanism is deduced for each sample type. Qualitatively, scattering and imaging give comparable results: plasticized samples are shown to behave close to a Fickian diffusion case, amorphous samples close to a case II. WAXS results also provide an in-depth knowledge of the crystalline structures associated to each step of the water ingress, and these are in turn correlated to water diffusion. To refine these observations, a recrystallized starch sample is also analyzed via WAXS. This study gives better insight into the structure of a material with a huge biomedical potential (as implants, for example), and for such applications, the behavior upon immersion in water is particularly relevant.

International audience; In foodstuffs, physico-chemical interactions and/or physical constraints between spores, inhibitors and food components may exist. Thus, the objective of this study was to investigate such interactions using a model emulsion as a microbial medium in order to improve bacterial spore control with better knowledge of the interactions in the formulation.Emulsions were prepared with hexadecane mixed with nutrient broth using sonication and were stabilized by Tween 80 and Span 80. The hexadecane ratio was either 35% (v/v) or 50% (v/v) and each emulsion was studied in the presence of organic acid (acetic, lactic or hexanoic) at two pH levels (5.5 and 6). Self-diffusion coefficients of emulsion components and the organic acids were measured by Pulsed Field Gradient-Nuclear Magnetic Resonance (PFG-NMR). The inhibition effect on the spore germination and cell growth of Bacillus weihenstephanensis KBAB4 was characterized by the measure of the probability of growth using the most probable number methodology, and the measure of the time taken for the cells to germinate and grow using a single cell Bioscreen® method and using flow cytometry. The inhibition of spore germination and growth in the model emulsion depended on the dispersed phase volume fraction and the pH value. The effect of the dispersed phase volume fraction was due to a combination of (i) the lipophilicity of the biocide, hexanoic acid, that may have had an impact on the distribution of organic acid between hexadecane and the aqueous phases and (ii) the antimicrobial activity of the emulsifier Tween 80 detected at the acidic pH value. The interface phenomena seemed to have a major influence. Future work will focus on the exploration of these phenomena at the interface.

Wheat starch-based model systems and wheat flour dough with the same water content (close to 45 %) were investigated upon heating (20–90 °C) using time-domain 1H NMR spectroscopy with the aim of assigning each spin–spin relaxation time (T 2) measured to a specific proton fraction. On the basis of the signal evolution according to Curie’s law for pure starch and pure water, temperature-associated changes for each T 2 value and their mass intensity were interpreted and assigned to water and/or biopolymer proton fractions related to the reversible swelling of starch or its gelatinization. The addition of 2 % (w/w) salt to model samples and dough induced few changes during the reversible swelling process but impacted on the measurements performed above 60 °C. Finally, studies performed on starch-based model systems improved understanding of the complex thermal processing of starch in dough by taking into account phenomena other than the starch swelling and gelatinization, such as gluten denaturation and changes in water–biopolymer interactions.

The dynamics of rigid dendrimer and flexible PEG probes in sodium caseinate dispersions and acid gels, including both translational diffusion and rotational diffusion, were studied by NMR. Above the onset of the close-packing limit (C ~ 10 g/100 g H2O), translational diffusion of the probe depended on its flexibility and on the fluctuations of the matrix chains. The PEG probe diffused more rapidly than the spherical dendrimer probe of corresponding hydrodynamic radius. The greater conformational flexibility of PEG facilitated its motion through the crowded casein matrix. Rotational diffusion was, however, substantially less hindered than the translational diffusion and depended on the local protein–probe friction which became high when the casein concentration increased. The coagulation of the matrix led to the formation of large voids, which resulted in an increase in the translational diffusion of the probes, whereas the rotational diffusion of the probes was retarded in the gel, which could be attributed to the immobilized environment surrounding the probe. Quantitative information from PFG-NMR and SEM micrographs have been combined for characterizing microstructural details in SC acid gels.

The thermal, dynamic, and structural properties of wheat starch–water systems with different levels of water content (11, 35, 40, 42, 45, and 50%, wet basis) were investigated. 1H time domain nuclear magnetic resonance (TD-NMR) spectroscopy was used to interpret and quantify the water transfer and starch transformations in terms of water uptake, granule swelling, amylose leaching, and melting of starch polymers in relation to the different levels of water content. Complementary differential scanning calorimetry (DSC) experiments were performed to study the effects of water content on the degree of starch gelatinization. In particular, this twofold approach was applied to the first endotherm to study the mechanisms of gelatinization with a common heating range both in NMR and DSC. It was shown that the trend of the enthalpy changes in the first phase transition in starch–water (SW) mixtures was strongly correlated with the loss of solid content measured by NMR in the corresponding temperature range (55–70 °C). Based on the evolution of the relative amplitudes of T 2, structural transformations of starch were shown to occur in both crystalline and amorphous regions within SW samples, supporting the fact that the amorphous phase of starch also plays a significant role in the phase transition of granules during gelatinization. This dynamic and hydrothermal approach provided the first NMR-based interpretation of the first endotherm measured by DSC.

International audience; The temperature-dependent changes in wheat starch powder and wheat starch-water mixtures were monitored in real-time throughout the heating/cooling program using a classical one-dimensional T1 method and a novel bi-dimensional approach to correlate spin-lattice and spin-spin relaxation times (T1-T2) including acquisition of the FID signal. The influence of two controlling factors (i.e. water content (11%, 35-50%, wet basis) and temperature (20-90 °C and back to 20 °C)) on water distribution and starch transformation was investigated. Quantitative analysis of 2D T1-T2 maps greatly facilitated the interpretation of T1 relaxation times, which have been interpreted rather narrowly in the literature when classically measured in one-dimension. Application of the new IR-FID-CPMG sequence allowed distinction between different proton pools with different T1 relaxation times, particularly when the starch gelatinization occurred. The quantification of each T1 component permitted to assign the short T1 to slow cross relaxation phenomena, highlighting proton chemical and/or diffusional exchanges between water and starch.

Arabinoxylans (AXs) extracted from wheat flour were characterized by using three different techniques of NMR spectroscopy. Liquid-state 1H NMR and solid-state 13C NMR allowed the investigation of the fine structure of the three specific fractions of AXs representative of the structural heterogeneity of AX in wheat tissues. Three pure AX fractions exhibiting an arabinose to xylose ratio of 0.33, 0.53, and 0.73 were compared relative to their substitution feature and also to their assembly into thin films. Measurements of M2, i.e. the second moment of proton dipolar interactions between the polysaccharide chains, were achieved using time-domain (TD) 1H NMR at different water contents and temperatures. Transitions of the M2 values were observed at a certain temperature close to the glass transition temperature Tg values of AXs in films. Comparison of the different AX films containing various water contents pointed out stronger dipolar interactions for lowly substituted AX. This indicated that, in films, contiguous unsubstituted xylan chains can interact together through hydrogen bonding resulting in a compact structure with small nanopores because of the lower chain motions and the shorter average distances between the lowly substituted AX chains. Copyright © 2012 John Wiley & Sons, Ltd.

International audience; To mimic the lamellar organisation of polymers within cereal cell walls, films of arabinoxylan (AX) and beta-glucan (BC) were prepared and characterized using Time-Domain (TD) H-1 NMR at different water contents and temperatures of measurement. The glass transition temperature (T-g) of the films was measured using differential scanning calorimetry (DSC). The investigation of M-2, i.e. the second moment of proton dipolar interactions, and T-2, i.e. the water spin-spin relaxation times, as a function of temperature and water content emphasized the complementary mechanisms involving the mobility of the polysaccharide chains both below and above the glass transition temperature, and the mobility of water molecules in interactions with the hydroxyl groups of the polysaccharides. In spite of the complexity of these mechanisms, we found that BC films featured higher M-2 values than AX films, which is consistent with higher proton intra- and inter-molecular dipolar interactions. These results, which are in agreement with the higher T-g obtained for BC films, were assigned to the smaller nanopores in the BC films which reduce the kinetics of the exchange between water molecules. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; In order to mimic the first steps of lignification, pectin/synthetic lignin (dehydrogenation polymers (DHPs)) interactions were investigated using reconstructing approaches. In artificially lignified bacterial cellulose(BC)/pectin composites, DHP nodules display a more dispersed distribution than in BC mats. Occurrence of covalent linkages between pectin and DHP was investigated by solid state NMR. Non-covalent bonds seem to govern the associative behaviour and stability of the complexes. Studied by small angle neutron scattering, a compaction process of DHP/pectin clusters occurs during polymerization and phase separation of the two polymers was shown at the nanometer scale.

Highly crystalline amylose complexes with menthone (1) and linalool (2) were analysed by wide-angle X-ray diffraction and solid-state nuclear magnetic resonance (NMR). The complexes, after partial water desorption in a controlled atmosphere ( a w = 0.75), displayed a typical V–isopropanol structure, showing the presence of ligand inside or between the helices in the crystalline domains. Sequential washing of the powdered complexes with ethanol before and after desorption permitted probing the intra- and inter-helical inclusions. High resolution magic angle spinning (HRMAS) recordings were used to compare the chemical shifts of free and bound aroma which allowed a proposal that some hydrogen bonding is involved in the amylose complexing. Moreover, it showed that free aroma was completely removed by ethanol washing. Using cross polarization magic angle spinning (CPMAS) and X-ray scattering experiments, it was demonstrated that the V–isopropanol type was retained for linalool whatever the treatment used. On the contrary, the measurement shifts toward the V–6I amylose hydrate (V–h) type for menthone after ethanol washing before the desorption step, reflecting the disappearance of inter-helical associations between menthone and amylose. The stability of the complex prepared with linalool shows that this ligand is more strongly associated to amylose helices. The discrepancies observed in the chemical shifts attributed to carbons C1 and C4 in CPMAS spectra of V–isopropanol and V–h forms could be attributed either to a deformation of the single helix (with possible inclusion of the ligand inside) or to the presence of the ligand between helices (only water molecules are present in the V–h form).

The chemical structure and interactions of the cell wall polysaccharides from the red edible seaweed Palmaria palmata were studied by liquid-like magic-angle-spinning (MAS) and cross-polarization MAS (CPMAS) solid-state 13 C NMR spectroscopy. The liquid-like MAS and CPMAS 13 C NMR spectra of the rehydrated algal powder revealed the presence of β-(1→4)/β-(1→3)-linked d -xylan with chemical shifts close to those observed in the solution 13 C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13 C NMR spectrum indicated that part of this cell wall polysaccharide is loosely held in the alga. The CPMAS NMR spectrum of the dry algal powder alcohol insoluble residue (AIR) showed broad peaks most of which corresponded to the mix-linked xylan. Hydration of AIR induced a marked increase in the signal resolution also in the CPMAS NMR spectra together with a shift of the C-3 and C-4 signals of the (1→3)- and (1→4)-linked xylose, respectively. Such modifications were present in the spectrum of hydrated (1→3)-linked xylan from the green seaweed Caulerpa taxifolia and absent in that of (1→4)-linked xylan from P. palmata . This result emphasizes the important role of (1→3) linkages on the mix-linked xylan hydration-induced conformational rearrangement. The mix-linked xylan signals were observed in the CPMAS NMR spectrum of hydrated residues obtained after extensive extractions by NaOH or strong chaotropic solutions indicating strong hydrogen bonds or covalent linkages. T 1 ρ relaxations were measured close or above 10 ms for the mix-linked xylan in the dry and hydrated state in AIR and indicated that the overall xylan chains likely remain rigid. Rehydration of the mix-linked xylan lead to a decrease in the motion of protons bounded to the C-1 and C-4 carbons of the (1→4)-linked xylose supporting the re-organization of the xylan chains under hydration involving junction-zones held by hydrogen bonds between adjacent (1→4)-linked xylose blocks. The CPMAS NMR spectrum of both dry and rehydrated residues obtained after NaOH and HCl extractions demonstrated the presence of cellulose and (1→4)-linked xylans. The structures of the different polysaccharides are discussed in relation to their interactions and putative functions on the cell wall mechanical properties in P. palmata .

International audience; Semiclatrate hydrate crystals of tetra-n-butyl ammonium bromide (TBAB) form at atmospheric pressure and a positive temperature. In suspension in water, they can be used as a heat transport medium or for gas separation. In terms of thermal energy storage and secondary refrigeration applications, TBAB hydrate slurries may be characterized by their flow properties under specific thermophysical conditions. The study presented here investigated one of these important properties, i.e. the crystal content, also called the solid fraction, that is usually estimated using the TBAB:H2O phase diagram. Our investigations revealed that Time-Domain Nuclear Magnetic Resonance (TD-NMR) relaxometry was remarkably sensitive to the solid content of TBAB:H2O hydrate slurries. Non-invasive and non-destructive measurements performed in real time demonstrated the power of NMR relaxometry to identify and quantify TBAB hydrates. Most importantly, NMR both measured and quantified type A and B hydrates, which no other technique can achieve without destroying the crystals or can only perform theoretically on the basis of a phase diagram, and thus without considering the possible conversion of type A to type B hydrates.

Composite films made with Arabinoxylans (AXs) (with high, middle and low level of substitution by arabinose) and (1 → 3)(1 → 4)-β- d -glucans (BGs) extracted from cereal cell walls have been prepared and analyzed using microscopy (SEM and LSCFM), DSC, mechanical tests and TD-NMR spectroscopy. The objectives were to correlate molecular and physico-chemical properties of films with mechanical and hydration properties of wheat cell walls. A phase separation phenomenon was observed for films made with highly substituted AXs and BGs at a ratio AX/BG of 60/40. This phase separation was correlated with lower dipolar interactions between polysaccharide chains and a decrease of ultimate strain and stress of films. Highly substituted AX and BG composite films exhibited very weak mechanical properties in agreement with weaker interactions between the polymer chains. This effect was supported by NMR results showing that interactions between AXs and BGs decreased with increased substitution of AXs in composite films. Lower dipolar interactions between polysaccharides favored the water mobility in relation with a higher specific surface area of polysaccharides in films but also higher distances between polysaccharide chains so larger nanopores in composite films made within highly substituted AXs. These multiscale characterizations agreed with the structural changes observed in wheat grain during its development.

Arabidopsis seeds rapidly release hydrophilic polysaccharides from the seed coat on imbibition. These form a heavy mucilage layer around the seed that makes it sink in water. Fourteen natural Arabidopsis variants from central Asia and Scandinavia were identified with seeds that have modified mucilage release and float. Four of these have a novel mucilage phenotype with almost none of the released mucilage adhering to the seed and the absence of cellulose microfibrils. Mucilage release was modified in the variants by ten independent causal mutations in four different loci. Seven distinct mutations affected one locus, coding the MUM2 β-D-galactosidase, and represent a striking example of allelic heterogeneity. The modification of mucilage release has thus evolved a number of times independently in two restricted geographical zones. All the natural mutants identified still accumulated mucilage polysaccharides in seed coat epidermal cells. Using nuclear magnetic resonance (NMR) relaxometry their production and retention was shown to reduce water mobility into internal seed tissues during imbibition, which would help to maintain seed buoyancy. Surprisingly, despite released mucilage being an excellent hydrogel it did not increase the rate of water uptake by internal seed tissues and is more likely to play a role in retaining water around the seed., Author Summary Seeds of the model plant Arabidopsis release sticky mucilage on imbibition that is constituted of complex polysaccharides. In this study, we have identified and characterised natural Arabidopsis variants that do not release mucilage and found that their seeds float. The accumulation of unreleased polysaccharides in the seed coat reduced water uptake rates on imbibition and would maintain buoyancy. We subsequently identified additional floating natural variants where mucilage is released, but is not attached to the seed, apparently due to defective cellulose production. The different variants arise from at least ten independent unique mutations and were collected from two discrete geographical areas. Arabidopsis seed flotation has thus evolved several times due to modifications in mucilage release. Released mucilage was found to retain water, but did not improve imbibition of internal seed tissues, indicating a role in maintaining seeds hydrated. These findings highlight the physical and potential physiological effects of mucilage production by the seed coat.

The use of ion-exchange chromatography and 31 P nuclear magnetic resonance ( 31 P NMR) to analyse the composition and the chain length of phosphate emulsifying salts were studied, as well as the impact of these salts in dairy products. Ion chromatography was more appropriate than 31 P NMR to study polyphosphate composition in complex environments, whereas interactions between phosphate species and dairy components were elucidated by 31 P NMR. Phosphate species interacting with calcium, as well as the percentage of chelated calcium, were identified using 31 P NMR. Thus, ion chromatography and solid-sate 31 P NMR could be used as complementary methods to study compositions of polyphosphate blends and their interactions with dairy matrices.

Article WOS:000320486000005; Arabinoxylans (AX) and (1 -> 3)(1 -> 4)-beta-D-glucans (BG) are the main components of the cell walls in the endosperm of wheat grain. The relative occurrence of these two polysaccharides and the fine structure of the AX are highly variable within the endosperm. Films of AX and BG were used as models of the cell wall to study the impact of polymer structure on the hydration and mechanical properties of the cell walls. Effective moisture diffusivities (D-eff) of AX and BG films were determined from 0 to 95% relative humidity (RH) at 20 degrees C. D-eff was influenced by the water content, and the structure of polysaccharides. Higher D-eff was obtained for films made with highly substituted AX compared to values obtained for films made with BG or lowly substituted AX. Proton dipolar second moments M-2 and water T-2 relaxation times measured by TD-NMR, indicated that the highly branched AX films exhibited a higher nano-porosity, favoring water motions within films. Results from! traction tests showed significant different mechanical properties between the AX and BG films. BG films exhibited much higher extensibility than AX films. Strength and extensibility of AX films decreased with increasing arabinose to xylose ratio. Our results show that the water motions and the mechanical properties of AX and BG films can be linked to the polysaccharide chains interactions that modulate the nanostructure of films.

International audience; The self-diffusion coefficients of different molecular weight PEGs (Polyethylene glycol) and casein particles were measured, using a pulsed-gradient nuclear magnetic resonance technique (PFG-NMR), in native phosphocaseinate (NPC) and sodium caseinate (SC) dispersions where caseins are not structured into micelles. The dependence of the PEG self-diffusion coefficient on the PEG size, casein concentration, the size and the mobility of casein obstacle particles are reported. Wide differences in the PEG diffusion coefficients were found according to the casein particle structure. The greatest reduction in diffusion coefficients was found in sodium caseinate suspensions. Moreover, sodium caseinate aggregates were found to diffuse more slowly than casein micelles for casein concentrations >9 g/100 g H2O. Experimental PEG and casein diffusion findings were analyzed using two appropriate diffusion models: the Rouse model and the Speedy model, respectively. According to the Speedy model, caseins behave as hard spheres below the close packing limit (10 g/100 g H2O for SC (Farrer & Lips, 1999) and 15 g/100 g H2O for NPC (Bouchoux et al., 2009)) and as soft particles above this limit. Our results provided a consistent picture of the effects of diffusant mass, the dynamics of the host material and of the importance of the casein structure in determining the diffusion behavior of probes in these systems.

Chlorogenic acid (5-caffeoylquinic acid) is a hydrophilic phenolic compound with antioxidant properties. Because of its high polarity, these properties may be altered when formulated in oil-based food. There is therefore an interest in trying to protect the natural antioxidant by molecular encapsulation. Amylose, the linear fraction of starch with essentially alpha(1-4) linkages, is well known for its ability to form semi-crystalline complexes with a variety of small ligands. Monoacyl lipids, as well as smaller ligands such as alcohols or flavor compounds, are able to induce the formation of left-handed amylose single helices. In contrast, chlorogenic acid is a bulky molecule whose topology requires the amylose helix to be distorted, which could prevent amylose complexation. An innovative strategy has been developed to overcome this problem by grafting an aliphatic chain onto chlorogenic acid then trapping this chain in the helical cavity. The lipophilization reaction was used to obtain a palmitoyl chlorogenic acid derivative and the amylose-palmitoyl chlorogenic acid assemblies were studied by X-ray diffraction, differential scanning calorimetry and NMR to elucidate the interaction. The results showed that such interactions between amylose and palmitoyl chlorogenic acid are effective. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; Chitosan particles were functionalized with ferulic acid (FA) and ethyl ferulate (EF) as substrates using laccase from Myceliophtora thermophyla as biocatalyst. The reactions were performed with chitosan particles under an eco-friendly procedure, in a heterogeneous system at 30 degrees C, in phosphate buffer (50 mM, pH 7.5).The FA-chitosan derivative presented an intense yellow-orange color stable while the EF-chitosan derivative was colorless. The spectroscopic analyses indicated that the reaction products bound covalently to the free amino groups of chitosan exhibiting a novel absorbance band in the UV/Vis spectra between 300 and 350 nm, at C-2 region by the duplication of C-2 signal in the C-13 NMR spectrum, via Schiff base bond (N=C) exhibiting novel bands in the FT-IR spectrum at 1640 and 1620 cm(-1). Additionally, antioxidant capacities of chitosan derivatives showed that the chitosan derivatives presented improved antioxidant properties, especially for FA-chitosan derivative (EC50 were 0.52 +/- 0.04, 0.20 +/- 0.02 mg/ml for DPPH center dot and ABTS(center dot+) scavenging, respectively). (C) 2011 Elsevier Ltd. All rights reserved.

International audience; Chemometric analyses of 13C CPMAS NMR spectra (without signal curve-fitting) recorded on celluloses from various origins and by varying the contact time of the cross-polarization process, indicated a direct relation between the crystallinity of cellulose and the PCA scores. The complex exponential increase of CPMAS signals was shown to be directly dependent on the cellulose crystallinity. Estimation of a crystallinity index was possible using the proton spin diffusion time values estimated by adjustment of the experimental NMR spectra obtained while cross-polarization built-up. Calculation of the corresponding lateral dimensions of cellulose crystallites has been carried out taking into account a variable thickness of the microfibrils surface layer. Using a multilinear regression method with a constraint of positivity (MLRC), modeling of the observed spectra of celluloses from various origins has been considered as a linear combination of available NMR spectra of pure forms (Iβ, Iα and amorphous forms). The concentration of these pure forms allowed a crystallinity index to be calculated as well as estimating the proportion of the cellulose Iβ allomorph. The proposed procedures based on chemometrics are rapid, robust, even on impure samples. They need no assumption about samples and very few manipulations of the NMR signals (no curve-fitting

International audience; The impact of homogalacturonans deficiency on the cell wall porosity of Arabidopsis thaliana QUA1 mutant was investigated using NMR measurements of protons mobility interpreted in terms of pore size variations at nanometer and micrometer scales. Isolation and purification of wild type and mutant stems and calli cell walls permitted to exacerbate the putative impact of the mutation on cellulose-hemicelluloses assembly in highly and poorly organised cell walls, respectively. NMR relaxation measurements of water and exchangeable biopolymer protons and self-diffusion processes of polyethylene glycol in walls informed about the porosity network density and heterogeneity. The role of pectins and proteins as well as the growth status of the cells on the wall porosity regulation are discussed.

International audience; Dystrophin is the genetically deficient protein in Duchenne Muscular Dystrophy. Its C- and N-terminal ends interact with cytoskeletal and membrane proteins, establishing a link between the cytoskeleton and the extracellular matrix. In a previous study, we showed that there is an interaction between the second repeat of the rod domain and membrane phospholipids, which places tryptophan residues in close contact with the membrane. Here, we examine the binding of the dystrophin repeat-2 to small unilamellar vesicles with varying composition. We find that the protein binds predominantly to di-oleyl-phosphatidylserine. The binding as a function of increasing mol% of DOPS appears to be cooperative due to reduction of dimensionality, greatly enhanced in the absence of salts, and partly modulated by pH. Substituting small by large unilamellar vesicles induces a 30-fold lower affinity of the protein for the membrane phospholipids. However, modifying the packing of the acyl chains by introducing lipids such as phosphatidylethanolamine and cholesterol to the vesicle leads to an approximately 7-fold increase in affinity. Taken together, these results show that the binding involves electrostatic forces in addition to hydrophobic ones.

In order to understand the role of sucrose synthase (SuSy) in carbon partitioning, metabolic fluxes were analyzed in maize root tips of a double mutant of SuSy genes, sh1 sus1 and the corresponding wild type, W22. [U-(14)C]-glucose pulse labeling experiments permitted the quantification of unidirectional fluxes into sucrose, starch and cell wall polysaccharides. Isotopic steady-state labeling with [1-(13)C]-, [2-(13)C]- or [U-(13)C]-glucose followed by the quantification by (1)H-NMR and (13)C-NMR of enrichments in carbohydrates and amino acids was also performed to determine 29 fluxes through central metabolism using computer-aided modeling. As a consequence of the suppression of SUS1 and SH1 isozymes, maize root tips diameter was significantly decreased and respiratory metabolism reduced by 30%. Our result clearly established that, in maize root tips, starch is produced from ADP-Glc synthesized in the plastid and not in the cytosol by sucrose synthase. Unexpectedly, the flux of cell wall synthesis was increased in the double mutant. This observation indicates that, in maize root tips, SH1 and SUS1 are not specific providers for cellulose biosynthesis.

International audience; The mechanism of lignin carbohydrate complex formation by addition of polysaccharides on quinone methide (QM) generated during lignin polymerisation was investigated using a model approach. Dehydrogenation polymers (DHPs, lignin model compounds) were synthesized from coniferyl alcohol in the presence of a glucuronoarabinoxylan (GAX) extracted from oat spelts, by Zutropfverfahren (ZT) and Zulaufverfahren (ZL) methods. The methods ZT and ZL differed in their distribution of QM over the reaction period but generated roughly the same QM amount. Steric exclusion chromatography of the ZT and ZL reaction products showed that only the ZT reaction produced high molar mass compounds. Covalent linkages in the ZT reaction involving ether bonds between GAX moiety and alpha carbon of the lignin monomer were confirmed by C-13 NMR and xylanase-based fractionation. The underlying phenomena were further investigated by examining the interactions between GAX and DHP in sorption experiments. GA! X and DHPs were shown to interact to form hydrophobic aggregates. In the ZT process, slow addition permitted polymer reorganisation which led to dehydration around the lignin-like growing chains thereby limiting the addition of water on the quinone methide formed during polymerisation and thus favoured lignin-carbohydrate complex (LCC) formation.

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International audience; The organisation of sugar beet and potato cell walls was studied using alkaline extractions following a response surface methodology, simultaneously with solid-state C-13 NMR spectroscopy. The influence of two extraction parameters: NaOH concentration (0.05, 0.275, 0.5 M) and temperature (40, 65, 90 degrees C) on the composition (neutral and acidic sugars) of the residues recovered was established. Treatments of increasing harshness progressively washed off non-cellulosic polysaccharides from the cell walls. Alkaline treatments applied to sugar beet cell wall material (SB-CWM) revealed the presence of diverse pectin populations. The existence of distinct pectin populations in potato cell wall material (P-CWM) was less outstanding. Solid-state C-13 NMR applied to SB-CWM and P-CWM and residues after treatment by 0.275 M NaOH at 65 degrees C revealed two fractions of pectic arabinan and galactan side chains. One fraction was highly mobile, whereas the other one displayed restricted mobility.

Cellulose microfibrils extracted from lemon and maize were studied by solid state NMR, Wide Angle X-ray Scattering, Fourier Transform Infrared Spectroscopy and Transmission Electron Microscopy. Some structural characteristics such as the allomorphic composition, the degree of crystallinity and the lateral or longitudinal crystal size were determined. These depended on the processing conditions, especially grinding, and determined the texturising properties of the microfibrils for liquid food product. Hydrolysed tunicin and Avicel were also studied as reference systems in terms of crystallinity and texturising properties in water. Lemon cellulose was shown to have a higher crystallinity or crystal size and a better texturising behaviour than maize microfibrils. Nevertheless, lemon microfibrils are more sensitive to grinding which decreases systematically the crystallinity and increases the amount of Iβ allomorph. Solid state NMR was also used to probe the mobility of the different regions of microfibrils by measuring T 1ρ which was well correlated to crystallinity. The presence of both surface and internal amorphous areas was discussed with respect to the NMR and X-ray scattering data. Some possible hypotheses for discrepancies observed between lemon and maize microfibrils in terms of texturising properties are expressed. Finally, these various properties were studied in the presence of polysaccharides such as carboxymethyl cellulose, scleroglucan or xanthan.