Films of arabinoxylans and β-glucans extracted from cereal grains: Molecular motions by TD-NMR

Polysaccharide-water interactions: NMR and DVS data

The data provided here relate to the research paper "Assessing the complementarity of TD-NMR, solid-state NMR and Dynamic Vapor Sorption in the characterization of polysaccharide-water interactions". The original data from TD-NMR, ss-NMR and DVS is provided in .dps, topspin and .xls formats respectively, allowing other authors to repeat our processing protocols using different parameters. We also include results obtained by varying the signal treatments. The analysis of these multimodal data have highlighted a variation in polysaccharide-water interactions depending on the type of assembly. These datasets are very useful for discriminating between water bound to polysaccharides and water absorbed or adsorbed into polysaccharide network, a key element in understanding interactions in these assemblies and an essential approach for developing tailor-made polysaccharides-based products.

Hydration and mechanical properties of arabinoxylan, (1,3;1,4)-β-glucan, and cellulose multilayer films simulating the cell wall of wheat endosperm

The cell walls of wheat endosperm, which play a pivotal role in seed germination, exhibit a laminated structure primarily composed of polysaccharides. In this study, composite multilayer films were prepared using arabinoxylan (AX), (1,3;1,4)-β-D-glucan (MLG), and cellulose nanofibers (CNFs), and the effect of polymer blend structure on cell wall hydration and mechanical properties was investigated. Atomic force microscopy and X-ray diffraction indicated that the network structure of MLG/CNF exhibits a higher degree of continuity and uniformity compared to that of AX/CNF. Mechanically, the extensive linkages between MLG and CNFs chains enhance the mechanical properties of the films. Moreover, water diffusion experiments and TD-NMR analysis revealed that water molecules diffuse faster in the network structure formed by AX. We propose a structural model of the endosperm cell wall, in which the CNFs polymer blend coated with MLG serves as the framework, and the AX network fills the gaps between them, providing diffusion channels for water molecules.

Determining whether granule structural or surface features govern the wheat starch digestion, a kinetic analysis

Deciphering the determinants of starch digestion from multiple interrelated properties is a challenge that can benefit from multifactorial data analysis. The present study investigated the digestion kinetic parameters (rate, final extent) of size-fractions from four commercial wheat starches with different amylose contents. Each size-fraction was isolated and characterized comprehensively using a large range of analytic techniques (FACE, XRD, CP-MAS NMR, time-domain NMR, DSC…). A statistical clustering analysis applied on the results revealed that the mobility of water and starch protons measured by time-domain NMR was consistently related to the macromolecular composition of the glucan chains and to the ultrastructure of the granule. The final extent of starch digestion was determined by the granule structural features. The digestion rate coefficient dependencies, on the other hand, changed significantly with the range of granule size, i.e. the accessible surface for initial binding of α-amylase. The study particularly showed the molecular order and the chains mobility predominantly limiting or accelerating the digestion rate depending on the accessible surface. This result confirmed the need to differentiate between the surface and the inner-granule related mechanisms in starch digestion studies.

Characteristics of the composite film of arabinoxylan and starch granules in simulated wheat endosperm

We found that cell wall components of wheat grains differed significantly across different grain-filling stages; specifically, we observed significant differences in water content and water migration rate (p < 0.05). A composite film of arabinoxylan and starch granules was prepared to simulate wheat endosperm structure. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), and thermogravimetric analysis (TGA) showed that the crystallinity and structural stability of the film increased with increasing starch content. Water diffusion experiments of the films revealed that the water diffusion rate gradually decreased with increasing starch content. Therefore, the water mobility of the starch endosperm was lower than that of the aleurone layer. These findings provide a basis for further studies in the context of wheat grain water regulation.

The use of time domain 1 H NMR to study proton dynamics in starch-rich foods: A review

Starch is a major contributor to the carbohydrate portion of our diet. When it is present with water, it undergoes several transformations during heating and/or cooling making it an essential structure-forming component in starch-rich food systems (e.g., bread and cake). Time domain proton nuclear magnetic resonance (TD ¹ H NMR) is a useful technique to study starch-water interactions by evaluation of molecular mobility and water distribution. The data obtained correspond to changes in starch structure and the state of water during or resulting from processing. When this technique was first applied to starch(-rich) foods, significant challenges were encountered during data interpretation of complex food systems (e.g., cake or biscuit) due to the presence of multiple constituents (proteins, carbohydrates, lipids, etc.). This article discusses the principles of TD ¹ H NMR and the tools applied that improved characterization and interpretation of TD NMR data. More in particular, the major differences in proton distribution of various dough and cooked/baked food systems are examined. The application of variable-temperature TD ¹ H NMR is also discussed as it demonstrates exceptional ability to elucidate the molecular dynamics of starch transitions (e.g., gelatinization, gelation) in dough/batter systems during heating/cooling. In conclusion, TD NMR is considered a valuable tool to understand the behavior of starch and water that relate to the characteristics and/or quality of starchy food products. Such insights are crucial for food product optimization and development in response to the needs of the food industry.

Glass Transition in Rice Pasta as Observed by Combined Neutron Scattering and Time-Domain NMR

Experimental protocols aiming at the characterisation of glass transition often suffer from ambiguity. The ambition of the present study is to describe the glass transition in a complex, micro heterogeneous system, the dry rice pasta, in a most unambiguous manner, minimising the influence of technique-specific bias. To this end, we apply an unprecedented combination of experimental techniques. Apart from the usually used NMR and DSC, we employ, in a concurrent manner, neutron transmission, diffraction, and Compton scattering. This enables us to investigate the glass transition over a range of spatio-temporal scales that stretches over seven orders of magnitude. The results obtained by neutron diffraction and DSC reveal that dry rice pasta is almost entirely amorphous. Moreover, the glass transition is evidenced by neutron transmission and diffraction data and manifested as a significant decrease of the average sample number density in the temperature range between 40 and 60 °C. At the microscopic level, our NMR, neutron transmission and Compton scattering results provide evidence of changes in the secondary structure of the starch within the dry rice pasta accompanying the glass transition, whereby the long-range order provided by the polymer structure within the starch present in the dry rice pasta is partially lost.

Effects of lamellar organization and arabinoxylan substitution rate on the properties of films simulating wheat grain aleurone cell wall

Herein, we evaluated the properties of alternate arabinoxylan (AX)/(1→3) (1→4)-β-D-glucan (BG) multilayer films. AX was extracted from wheat at three growth stages and single-component and alternate overlapping multilayer films were prepared. The physical properties, water diffusion rate, and water mobility of multilayer films during water absorption and desorption were studied. There were significant differences in the AX content and arabinose-to-xylose ratio at different growth stages. The LAX/BG multilayer films showed excellent thermal stability and mechanical properties with an increase in the relative humidity. The AX multilayer films with a low substitution rate showed a better water-binding capacity, whereas water molecules in films with a high substitution rate showed higher mobility. Therefore, a low substitution rate AX and AX/BG composite structure can improve the thermodynamic properties of multilayer films, but limit water mobility. We provide new insights on the physicochemical properties and water-regulation effects of wheat cell wall.

Variation in cell wall structure and composition of wheat grain based on geography and regulatory effect of cell wall on water mobility

Wheat grain from 12 different regions in China was used to study variations in the cell wall structure and chemical composition based on geography. The mobility and migration rate of water in wheat grain during moisture absorption and drying were determined under different relative humidity conditions. Depending on the geography, variations were noted in the thickness and component content of the wheat grain cell wall. Cell wall thickness was positively correlated with the total arabinoxylan (TAX) content. Cell wall thickness and TAX content of the aleurone layer were positively correlated with altitude and negatively correlated with longitude. The water migration rate decreased with the increase of cell wall thickness and TAX content. Nuclear magnetic resonance (NMR) results revealed that grains with thick aleurone cell wall showed increased molecular mobility of water. These findings lay the foundation for further study of water regulation in wheat cell wall.

Two dimensional IR-FID-CPMG acquisition and adaptation of a maximum entropy reconstruction

By acquiring the FID signal in two-dimensional TD-NMR spectroscopy, it is possible to characterize mixtures or complex samples composed of solid and liquid phases. We have developed a new sequence for this purpose, called IR-FID-CPMG, making it possible to correlate spin-lattice T1 and spin-spin T2 relaxation times, including both liquid and solid phases in samples. We demonstrate here the potential of a new algorithm for the 2D inverse Laplace transformation of IR-FID-CPMG data based on an adapted reconstruction of the maximum entropy method, combining the standard decreasing exponential decay function with an additional term drawn from Abragam's FID function. The results show that the proposed IR-FID-CPMG sequence and its related inversion model allow accurate characterization and quantification of both solid and liquid phases in multiphasic and compartmentalized systems. Moreover, it permits to distinguish between solid phases having different T1 relaxation times or to highlight cross-relaxation phenomena.

Characterization of Oat (Avena nuda L.) β-Glucan Cryogelation Process by Low-Field NMR

Low-field nuclear magnetic resonance (LF-NMR) is a useful method in studying the water distribution and mobility in heterogeneous systems. This technique was used to characterize water in an oat β-glucan aqueous system during cryogelation by repeated freeze-thaw treatments. The results indicated that microphase separation occurred during cryogelation, and three water components were determined in the cryostructure. The spin-spin relaxation time was analyzed on the basis of chemical exchange and diffusion exchange theory. The location of each water component was identified in the porous microstructure of the cryogel. The pore size measured from the SEM image is in accordance with that estimated from relaxation time. The formation of cryogel is confirmed by rheological method. The results suggested that the cryogelation process of the polysaccharide could be monitored by LF-NMR through the evolution of spin-spin relaxation characteristics.

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.

An unconventional approach for improving the integrity and mechanical properties of xylan type hemicellulose based films

Inclusion of the salt KAcO into hemicellulose based polymeric films results in improved film formation and mechanical properties. Considering this beneficial effect of KAcO, its separation during the hemicellulose isolation process is not always a necessity for film production.