Time-domain Nuclear Magnetic Resonance Research Articles

Physicochemical and sensorial properties of tomato leathers at different drying conditions.

Tomato leather as a healthy alternative to traditional fruit leathers was formulated. A tray dryer with changing temperature (50, 60, and 70°C) and relative humidity (5%, 10%, and 20%) was used to achieve the best product in terms of color, water distribution, lycopene content, mechanical, and sensorial properties. Color change was the highest at 70°C due to the Maillard reaction. Lycopene content was also the highest at 70°C. Time domain-NMR relaxometry showed that water distribution of all samples was homogeneous and similar to each other. Processing conditions affected mechanical properties significantly. The highest tensile strength was observed at 70°C, possibly due to the denatured proteins. Sensory analysis indicated better flavor development at 70°C, whereas overall acceptability of samples was higher at 50°C. The results of this study showed the main processing parameters of tomato leather with a minimal amount of ingredients, with acceptable mechanical and sensorial properties. PRACTICAL APPLICATION: Tomato leather was produced by using minimal amount of ingredients. Taste of the leather was found acceptable, as a salty snack food. Therefore, this product can be produced economically and it has a high potential to be consumed as an alternative to conventional fruit leathers.

Understand and characterize draining of acid milk gels using Magnetic Resonance Imaging and Time Domain-Nuclear Magnetic Resonance

Understand and characterize draining of acid milk gels using Magnetic Resonance Imaging and Time Domain-Nuclear Magnetic Resonance

Disaggregation and fibrillation during sol-gel transition of alginate hydrogels

The rheological and morphological characteristics of Ca-crosslinked alginate hydrogels with two different M/G ratios, α-L-guluronate (G)-rich and β-D-mannuronate (M)-rich, each with one alginic acid concentration, were investigated. It was found that the stiffness and elasticity of alginate hydrogels are derived from the thickness and density of the fibril network structures. In aqueous alginate solution, ball-like aggregates of alginates are present. Time-resolved small-angle X-ray scattering and time-domain nuclear magnetic resonance measurements suggest that the disaggregation of alginate aggregates and loose fibrillation occur in the early stage of the sol-gel transition. After these induction stage, direct gelation is finally caused by the formation of the egg-box junction. G-rich alginate hydrogel has a higher stiffness and a thicker and denser fibril network structure than M-rich alginate hydrogel. The former also exhibits faster and more significant changes in physical properties during the sol-gel transition.

Unravelling temperature-dependent molecular changes in hydrated wheat and maize starches using 1H time-domain NMR

This study proved that time-domain NMR (TD-NMR) experiments can accurately demonstrate the interaction between starch (wheat and maize) and water and the distribution of water molecules in starch-water systems during heating. Molecular properties in starch-water systems at 50% moisture content were monitored by Rhim and Kessemeier – Radiofrequency Optimized Solid-Echo (RK-ROSE) and Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences at frequent (2 °C intervals) measurements during heating (55–80 °C). Starch-like and water-like phases were obtained by RK-ROSE and CPMG pulse sequences, respectively. The second moment, M2, along with the relaxation times of the populations, associated with fast-decaying protons, provided information on the crystal structure state during heating and the extent of gelatinisation. The relaxation times of the most abundant population from the CPMG signal decreased during heating due to strong interactions between starch and water. Temperature of stabilisation of this population aligned with the associated findings from the differential scanning calorimetry and rheological measurements.

Designing Sustainable Hydrophilic Interfaces via Feature Selection from Molecular Descriptors and Time-Domain Nuclear Magnetic Resonance Relaxation Curves.

Surface modification using hydrophilic polymer coatings is a sustainable approach for preventing membrane clogging due to foulant adhesion to water treatment membranes and reducing membrane-replacement frequency. Typically, both molecular descriptors and time-domain nuclear magnetic resonance (TD-NMR) data, which reveal physicochemical properties and polymer-chain dynamics, respectively, are required to predict the properties and understand the mechanisms of hydrophilic polymer coatings. However, studies on the selection of essential components from high-dimensional data and their application to the prediction of surface properties are scarce. Therefore, we developed a method for selecting features from combined high-dimensional molecular descriptors and TD-NMR data. The molecular descriptors of the monomers present in polyethylene terephthalate films were calculated using RDKit, an open-source chemoinformatics toolkit, and TD-NMR spectroscopy was performed over a wide time range using five-pulse sequences to investigate the mobility of the polymer chains. The model that analyzed the data using the random forest algorithm, after reducing the features using gradient boosting machine-based recursive feature elimination, achieved the highest prediction accuracy. The proposed method enables the extraction of important elements from both descriptors of surface properties and can contribute to the development of new sustainable materials and material-specific informatics methodologies encompassing multiple information modalities.

Rapid Measurement of Magnetic Particle Concentrations in Wildland–Urban Interface Fire Ashes and Runoff Using Compact NMR

Wildfires are increasing in size, frequency, and intensity, releasing increased amounts of contaminants, including magnetic particles, into the surrounding environment. The aim of this paper is to develop a sensing method for the detection and quantification of magnetic particles (MPs) in fire ash and fire runoff using a compact Time-Domain Nuclear Magnetic Resonance (TD-NMR) system. The system is made up of custom NMR electronics with a compact and rugged permanent magnet array designed to enable future deployment as an in situ sensor. A signal-to-noise ratio of 25 dB was measured for a single scan, and sufficient data can be acquired in one minute. A linear relationship with an R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 0.9699 was established between transverse relaxation rates and MP concentrations in ash samples. This was validated by testing known dilutions of pure magnetite particles and showing that they fit within the same linear curve. The developed approach was then applied to detect MPs in surface water, where changes in the relaxation rates as high as 400% were observed before and after a wildfire event. MPs were removed from the surface water using a magnetic particle separator to confirm that observed changes were solely due to the presence of MPs. The compact NMR system can be used as a simple and rapid approach to track and quantify the concentrations of magnetic particles released from fire ashes and also from other sources such as discharges from coal ash and other combustion ashes.

Time domain NMR evaluation of thermal and thermochemical aging of nitrile rubber on crosslinking and mechanical properties

This study investigates the impact of aging on nitrile rubber (NBR) compositions under thermal and thermochemical aging conditions. The effects of aging were assessed using the 1H Double Quantum Time Domain NMR (DQ-NMR) technique, providing molecular-scale insights into average cross-link density, spatial heterogeneity, and network inelastic defects. The aging's influence on the macroscopic mechanical properties of NBR, including hardness, elongation, and stress at break, known to be closely related to cross-linking, was examined. It was observed that temperature-induced aging affected NBR differently based on the acrylonitrile content and solvent absorption capacity. 1H Double Quantum Time Domain NMR provided evidence of increasing heterogeneous cross-linking, which created a denser network structure. The changes in mechanical properties during aging were consistent with the NMR analyses, providing valuable insights for understanding, customizing, and predicting the service life of a specific O-Ring based NBR formulation.

Behavior of endo-xylanases on wheat milling products in relation with variable solid loading conditions

To investigate the incubation conditions encountered by enzymes in cereal-based product transformation processes, this study aims to provide comprehensive information on the effect of low (18 %) to high (72 %) solid loading on the behavior of bacterial and fungal xylanases towards wheat grain fractions, i.e. white flour, ground whole grain and bran. Both enzymes are effective from 30 % water content. A water content of 50 % appears as the threshold for optimal arabinoxylan solubilisation. The specificity of enzymes was influenced by low hydration conditions, particularly in wheat bran, which contains arabinoxylan with diverse structures. Especially the bacterial xylanase became more tolerant to arabinose substitution as the water content decreased. Time Domain-NMR measurements revealed four water mobility domains in all the fractions. The water populations corresponding to 7.5 nm to 15 nm pores were found to be the most restrictive for enzyme activity. These results define the water content limits for the optimal xylanase action in cereal products.

Correlation of low field nuclear magnetic resonance relaxation with composition and glass transition of hard candies

Hard candies produced from sucrose and doctoring agents such as glucose syrup (GS) and high fructose corn syrup (FS) have been investigated in terms of their final composition, glass transition temperature (Tg), degree of crystallinity, total soluble solids (TSS) content and water activity (aw). Time domain (TD) 1H NMR longitudinal relaxation time (T1) and second moment (M2) measurements have been used to understand the glassy state and crystallization characteristics for different hard candy formulations. The investigated candies include sucrose as the main sugar component. Different levels of doctoring agents have been mixed with sucrose to obtain products with different characteristics. It has been shown that addition of any doctoring agent to sucrose formulations decreases the Tg of the system significantly (p≤ 0.05). Furthermore, GS or FS addition also induce significant changes in TSS and aw. T1 and M2 results are almost parallel to each other, both reaching the highest values for the highest sucrose concentration (p≤ 0.05). The results demonstrate that the glass transition and crystallization characteristics of hard candy formulations can be monitored and analyzed by TD NMR relaxometry, alternative to other frequently used conventional methods including differential scanning calorimetry (DSC) and X-ray diffraction.

Study of the surface, rheological and morphological characteristics of isotactic polypropylene microplastics aged in a photothermal oxidation chamber

The aim of this study was to investigate, in addition to degradation processes, the rheological, crystalline, and molecular dynamics changes in isotactic polypropylene microplastics with average sizes of 0.5 and 2 mm, aged in a photothermal oxidation chamber for 166 days. In addition to commonly used techniques in microplastics research, time-domain nuclear magnetic resonance (TD-NMR) in fast field cycling and fixed field modes, was employed for the first time in the study of these materials, providing non-destructive information that supports other results. Concurrently with X-ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), rheometry, Fourier-transform infrared spectroscopy (FTIR), surface wettability, and scanning electron microscopy (SEM) techniques, two antagonistic phenomena were observed over the aging period. One associated with the surface degradation of microplastics and increased molecular mobility, and the other related to morphological changes in the internal layers, leading to increased rigidity. These phenomena occur slightly differently depending on the average particle size. Through multivariate data analysis with principal component analysis (PCA) and hierarchical cluster analysis (HCA), it was possible to determine that the degradation process intensifies after 62 days of simultaneous exposure to ultraviolet radiation, temperature, and oxidizing atmosphere. The obtained data highlight that even synthetic polymers with long degradation periods can undergo, in the form of microplastics, initial morphological changes in just 15 days and degradation processes within a few months of exposure to weathering conditions.

Effect of Adding Bentonite to Porous Silica via the Sol-Gel Method.

The control of specific surface area and pore size of porous materials is essential for applications such as optics, medicine, and food technology. Here, the interspace between nanomaterials such as nanoparticles and nanosheets was studied. Nanoparticle-nanosheet interspaces were formed by incorporating bentonite nanosheets to the preparation of porous silica by the sol-gel method. The product had micropore and mesopores, which originated from internanoparticle space and nanoparticle-nanosheet spaces, respectively. These two types of pores had not only different sizes but also different aspect ratios. Time-domain nuclear magnetic resonance evaluation of the bentonite dispersion revealed that the dispersion state of bentonite in water prior to composite fabrication affected the formation of the pore structure. The pore size distribution could be easily changed by adding two-dimensional and flexible nanosheets owing to the change in the physical properties of the product. The silica-bentonite composite had a significantly larger specific surface area and pore volume than porous silica without bentonite. Water vapor adsorption measurements showed that the composite exhibited a larger maximum adsorption in comparison to porous silica. Therefore, a large improvement in the physical properties can be achieved by combining nanomaterials with different geometries.

High-Throughput, Nondestructive, and Biosafe Method to Accurately Quantify Water Content in Human Fecal Samples by Benchtop 1H TD-NMR Analysis for Downstream Bioanalytical and Clinical Uses.

Water or moisture content in human stool samples is an important parameter for bioanalytical and clinical purposes. For bioanalytical use, accurate quantitation of water content in stool can provide the extent of dilution within the stool sample which can further be used for absolute quantitation of various stool based biomarkers. For clinical use, water or moisture content in stool is an important indicator of gastrointestinal health, and its accurate determination can enable quantitative assessment of the Bristol Stool Form Scale. In general, accurate determination of water content of stool samples is cumbersome, low-throughput process and is prone to harmful stool pathogens biocontamination, sample cross-contamination using techniques such as gravimetry and karl fischer titration. Here, we report a novel user-friendly high-throughput method to quantitatively and accurately measure the overall water content in human fecal samples nondestructively and biocontained in a closed tube using benchtop a 1H time domain nuclear magnetic resonance analyzer. We used gravimetry and measurement of various bile acid metabolites in stool to verify the accuracy and robustness of the water content measurement using this technique.

Elm wood (Ulmus rubra) vacuum drying at 40 °C studied by time domain nuclear magnetic resonance (TD-NMR)

Abstract The time domain nuclear magnetic resonance (TD-NMR) technique was employed to distinguish various water states, and the moisture migration during Elm wood (Ulmus rubra) heartwood vacuum drying was quantitatively analyzed. The transverse relaxation time (T2) was employed to establish the correlation between drying time and moisture migration. Additionally, the longitudinal relaxation time (T1) was utilized to identify two types of water states within the cell wall: OH bound water (B-water) and more freely bound water (C-water). Meanwhile, the changes in these two types of bound water during the drying were investigated. The results demonstrated an exponential decrease in the content of OH bound water and more freely bound water with drying time. OH bound water within the cell wall predominated, with only a small portion of more freely bound water experiencing migration loss when the moisture content (MC) dropped below 20 %. Furthermore, OH bound water exhibited higher migration rate compared to more freely bound water at 10–20 % MC, while the motion of OH bound water molecules became highly restricted and stronger binding to cell walls than more freely bound water at a MC level of below 10 %. These findings yield a theoretical foundation and empirical support for optimizing drying methods.

Determination of nuclear magnetic resonance surface relaxivity for the macropore system from wood cell lumen

To determine the surface relaxivity of pores plays a vital role in the application of time-domain nuclear magnetic resonance (TD-NMR) technology to porous structure characterization for wood. Currently, the surface relaxivity of pores is calibrated using a standard sample with a pore size of the same order as the wood pore system. However, the uniformly distributed pore size of standard sample is unfit to accurately indicate the complexity of porous structure of wood, which significantly affects the accuracy of test results. By integrating the TD-NMR technology with mercury intrusion porosimetry (MIP), the surface relaxivity of macropores in the lumen of wood cells is calibrated in this study using the tested sample, so as to avoid the error in measurement as caused by existing method. Data processing is performed using several mathematical methods including interpolation arithmetic and least square principle. Notably, the node segmentation method is applied to identify the T2 boundary of pores in cell lumen and to classify the porous structure of cell lumen into different pore systems. The approach proposed in this study is demonstrated to be effective in improving the accuracy of TD-NMR technology for characterizing the porous structure of wood. Also, it contributes a potential solution to accounting for the porous structure of wood based on the phenomenon of pore relaxation, which can improve the understanding of wood pore conformation.

Quality control of hazelnut-based spreads: 1H TD-NMR transverse relaxation

Hazelnut-based spreads are very popular, and they are available in a variety of compositions and prices. They, therefore, require detailed quality control and reliable fraud detection regarding the substitution of high-cost cocoa butter. Transverse relaxation measured via 1H time domain NMR (TD-NMR) is an approach that is compatible with industrial quality control but allows an in-depth insight into the materials. When transverse relaxation is measured as a function of temperature in a moderate range T ϵ [253, 353] K, the melting of cocoa butter and palm oil can be studied. The observations can be taken as a basis for quality control as the prices of these two components are significantly different. Fats introduce different qualities to the spreads in addition. This paper describes the experimental procedure and the findings on a spread sample basis with a considerable span width regarding the ingredients of commercially available hazelnut-based spreads.

Quantitative evaluation of adsorption behavior of carboxymethylcellulose on carbon nanotubes by time-domain NMR with the aim of obtaining stable dispersions

This study applied time domain NMR (TD‐NMR) to investigate the effect of carboxymethylcellulose (CMC) adsorption on the dispersion of carbon nanotubes (CNTs) in water. In many aqueous dispersions, the relaxation time measured by TD‐NMR is dominated by bound water on the particle surface. In contrast, since CMC molecules are adsorbed on the hydrophobic surface of CNTs, we proposed a model where relaxation times of hydration water of CMC adsorbed on CNTs, hydration water of free CMC, and bulk water are dynamically averaged in the TD‐NMR measurement. In this study, conversely, we presented the procedure to calculate the fraction of CMC adsorbed on CNTs from the measured relaxation time. Since the adsorbed layer of CMC can stabilize CNTs, the amount of adsorbed CMC is expected to be closely related to the dispersion state of CNTs. TD‐NMR measurements of CNT slurrys with different CMC concentrations showed that the adsorption ratio reached almost 100% (adsorption saturation) when the CMC concentration became larger than that of CNTs. At the adsorption saturation, it was confirmed that the CNT slurry exhibited the lowest apparent viscosity, and the model electrode showed the highest electro-conductivity. In addition, we demonstrated that the adsorption ratio is helpful to assess the dispersion state of CNTs and to optimize the dispersion process. The current study showed that TD‐NMR is very useful for quantitative evaluation of sterically stabilized dispersions because it can evaluate the adsorption rate of adsorbed polymers without dilution.

Multi-scale investigation of the heat-induced transformation of starch in model dough and starch systems

Our study investigated the impacts of starch botanical origin (tapioca versus wheat starch) and gluten addition on the water distribution and hydrothermal changes of starch in model dough systems compared to their pure starch counterparts. In it, we employed a combination of time-domain nuclear magnetic resonance (TD-NMR), wide angle X-ray diffraction (WAXD), solid state nuclear magnetic resonance (ssNMR) at variable temperature (VT) and differential scanning calorimetry (DSC) measurements. The results showed that at intermediate hydration levels, water ingress into starch granules, increase in glucan chain mobility, and dissociation of double helices (DH) of amylopectin occurred at lower temperatures than crystallite loss of order and melting. The inhibitory effect of gluten on wheat starch hydrothermal changes was explained by a higher water adsorption capacity of gluten compared to starch at this hydration level (50%, wb). However this effect was shown to be influenced by starch botanical origin, tapioca-based systems showing no hindrance effect of gluten on starch-water interaction. The study also provides additional evidence for the sensitivity and detection scales of the different techniques at 50% water content.

Water migration mechanism during internal curing of cement composites with cellulose microfibers

This study aimed to investigate the internal curing mechanism of cement composites containing cellulose microfibers (CMFs) derived from kenaf stalk bast. The primary test variable was the CMF content, which controlled the amount of water absorbed by the CMFs, thereby facilitating internal curing. The evolution of proton signals from time-domain nuclear magnetic resonance (NMR) was analyzed for the solid phases and various mobile water components during the curing process. The NMR results showed strong correlation with the thermal decomposition and degree of hydration, as determined by thermogravimetry and quantitative X-ray diffraction, respectively. The higher CMF content led to a delayed onset of hydration at early age. Moreover, the internal curing process was supported by the delay in the detection time of the solid-phase signal and an increase in signal intensities of the interlayer water and solid components, indicating the formation of hydrated phases. These insights clarify the significant role of CMFs in enhancing internal curing effects in cement composites.

Absence of Slc39a14/Zip14 in mouse pancreatic beta cells results in hyperinsulinemia.

Zinc is an essential component of the insulin protein complex synthesized in β cells. The intracellular compartmentalization and distribution of zinc are controlled by 24 transmembrane zinc transporters belonging to the ZnT or Zrt/Irt-like protein (ZIP) family. Downregulation of SLC39A14/ZIP14 has been reported in pancreatic islets of patients with type 2 diabetes (T2D) as well as mouse models of high-fat diet (HFD)- or db/db-induced obesity. Our previous studies observed mild hyperinsulinemia in mice with whole body knockout of Slc39a14 (Zip14 KO). Based on our current secondary data analysis from an integrative single-cell RNA-seq dataset of human whole pancreatic tissue, SLC39A14 (coding ZIP14) is the only other zinc transporter expressed abundantly in human β cells besides well-known zinc transporter SLC30A8 (coding ZnT8). In the present work, using pancreatic β cell-specific knockout of Slc39a14 (β-Zip14 KO), we investigated the role of SLC39A14/ZIP14-mediated intracellular zinc trafficking in glucose-stimulated insulin secretion and subsequent metabolic responses. Glucose-stimulated insulin secretion, zinc concentrations, and cellular localization of ZIP14 were assessed using in vivo, ex vivo, and in vitro assays using β-Zip14 KO, isolated islets, and murine cell line MIN6. Metabolic evaluations were done on both chow- and HFD-fed mice using time-domain nuclear magnetic resonance and a comprehensive laboratory animal monitoring system. ZIP14 localizes on the endoplasmic reticulum regulating intracellular zinc trafficking in β cells and serves as a negative regulator of glucose-stimulated insulin secretion. Deletion of Zip14 resulted in greater glucose-stimulated insulin secretion, increased energy expenditure, and shifted energy metabolism toward fatty acid utilization. HFD caused β-Zip14 KO mice to develop greater islet hyperplasia, compensatory hyperinsulinemia, and mild insulin resistance and hyperglycemia. This study provided new insights into the contribution of metal transporter ZIP14-mediated intracellular zinc trafficking in glucose-stimulated insulin secretion and subsequent metabolic responses.NEW & NOTEWORTHY Metal transporter SLC39A14/ZIP14 is downregulated in pancreatic islets of patients with T2D and mouse models of HFD- or db/db-induced obesity. However, the function of ZIP14-mediated intracellular zinc trafficking in β cells is unknown. Our analyses revealed that SLC39A14 is the only Zn transporter expressed abundantly in human β cells besides SLC30A8. Within the β cells, ZIP14 is localized on the endoplasmic reticulum and serves as a negative regulator of insulin secretion, providing a potential therapeutic target for T2D.

Assessing the complementarity of time domain NMR, solid-state NMR and dynamic vapor sorption in the characterization of polysaccharide-water interactions

Characterizing the hygroscopic behavior of macromolecular assemblies is crucial for understanding biological processes as well as to develop tailor-made polysaccharides-based products. In this work, assemblies consisting of nanocelluloses (CNC or CNF) and/or glucomannan in different ratio were studied at different water activity levels, using a multi-analytical approach that combined Dynamic Vapor Sorption (DVS), Time-Domain Nuclear Magnetic Resonance (TD-NMR) and solid-state NMR (ss-NMR). The water retention capacity of the films, as a function of their composition, showed that an enrichment in konjac glucomannan in association with cellulose increased the water absorption capacity but decreased the water retention capacity. In addition, the combination of CNC and glucomannan appears to reduce the water absorption capacity of each polymer. Correlating the findings from the various methods allowed us to propose the use of TD-NMR data for predicting the water retention capacity. These results, summarized in a schematic representation, offer new insights into the organization of water molecules in polysaccharide assemblies in various humidity conditions.