Corinne Rondeau-Mouro

Structural features and potential texturising properties of lemon and maize cellulose microfibrils

Abstract 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.

Solid-state 13C NMR spectroscopy studies of xylans in the cell wall of Palmaria palmata (L. Kuntze, Rhodophyta).

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 13C NMR spectroscopy. The liquid-like MAS and CPMAS 13C NMR spectra of the rehydrated algal powder revealed the presence of beta-(1-->4)/beta-(1-->3)-linked D-xylan with chemical shifts close to those observed in the solution 13C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13C 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 rho) 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.

Studies of xylan interactions and cross-linking to synthetic lignins formed by bulk and end-wise polymerization: a model study of lignin carbohydrate complex formation

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 α carbon of the lignin monomer were confirmed by 13C NMR and xylanase-based fractionation. The underlying phenomena were further investigated by examining the interactions between GAX and DHP in sorption experiments. GAX 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.

Local Evolution of Seed Flotation in Arabidopsis

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.

Hydration and mechanical properties of arabinoxylans and β-D-glucans films.

Arabinoxylans (AX) and (1→3)(1→4)-β-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 (Deff) of AX and BG films were determined from 0 to 95% relative humidity (RH) at 20°C. Deff was influenced by the water content, and the structure of polysaccharides. Higher Deff 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 M2 and water T2 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.

Coupling lipophilization and amylose complexation to encapsulate chlorogenic acid

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 α(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.

Water mobility within arabinoxylan and β-glucan films studied by NMR and dynamic vapour sorption

BACKGROUND The main purpose of this research was to determine the impact of the structure and organisation of polysaccharides on the hydration properties of the cell walls of cereal grains. In order to remodel the lamellar assembly of arabinoxylan (AX) and (1 → 3)(1 → 4)-β-D-glucan (BG) within the endosperm cell walls, films were prepared and analysed using dynamic vapour sorption and time domain nuclear magnetic resonance spectroscopy. RESULTS The water diffusivities within the AX and BG films were measured at 20 °C by observing the water sorption kinetics within a mathematical model based on Ficks second law. The evolution of spin-spin relaxation times of water protons measured by increasing the temperature is explained by the additional contributions of motion of the protons of polysaccharides and/or rapid chemical exchanges of protons between water and hydroxyl groups of polysaccharides. CONCLUSION The difference between patterns of water behaviour within the AX and BG films can be related to the difference in their nanostructures. The smaller nanopores of the BG films cause their nanostructure to be more compact.

Study of triacylglycerol polymorphs by nuclear magnetic resonance: effects of temperature and chain length on relaxation parameters.

It is very important to monitor the characteristics of triacylglycerol crystal network in fats, as these crystals have an impact on many food properties such as texture, sensory taste, and extended shelf life. Although time‐domain NMR (TD‐NMR) is now the reference technique to determine the solid fat index in food, the entire possibilities of this technique are not used. Some NMR studies have been performed to determine its power for the discrimination of polymorphism. In this study, extended investigations proved that TD‐NMR could evaluate triacylglycerol (TA) polymorphism, independently from temperature and chain length. Study of the dipolar interactions through second moment M2, which is characteristic of proton mobility in solid‐state samples, provided a new understanding of the structural organization of crystal molecules. Proton spin–lattice relaxation, which has been proved to be a true probe of polymorphism, has provided information on crystal networks. Combination of the two techniques revealed two very interesting kinds of results, i.e. the presence of a minimum spin–lattice relaxation time T1 for tristearin α, which is a characteristic of a dynamic molecular process, and differences in behavior between long and short chain lengths, both at a molecular and a crystal level. Copyright

Distribution and mobility of phosphates and sodium ions in cheese by solid-state 31P and double-quantum filtered 23Na NMR spectroscopy

The feasibility of solid‐state magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) spectroscopy and 23Na NMR spectroscopy to investigate both phosphates and Na+ ions distribution in semi‐hard cheeses in a non‐destructive way was studied. Two semi‐hard cheeses of known composition were made with two different salt contents. 31P Single‐pulse excitation and cross‐polarization MAS experiments allowed, for the first time, the identification and quantification of soluble and insoluble phosphates in the cheeses. The presence of a relatively ‘mobile’ fraction of colloidal phosphates was evidenced. The detection by 23Na single‐quantum NMR experiments of all the sodium ions in the cheeses was validated. The presence of a fraction of ‘bound’ sodium ions was evidenced by 23Na double‐quantum filtered NMR experiments. We demonstrated that NMR is a suitable tool to investigate both phosphates and Na+ ions distributions in cheeses. The impact of the sodium content on the various phosphorus forms distribution was discussed and results demonstrated that NMR would be an important tool for the cheese industry for the processes controls. Copyright

Multiscale characterization of arabinoxylan and β-glucan composite films

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.