Low-resolution Nuclear Magnetic Resonance Research Articles

Improved Methods for Characterizing Emulsions by Low-Resolution Nuclear Magnetic Resonance via Surface Relaxation and One-Dimensional Images

The use of nuclear magnetic resonance (NMR) is an appropriate tool for studying colloids in a non-invasive manner. Droplet size distributions and one-dimensional sample profiles are readily produced to characterize an emulsion, its stability, the size distribution of the dispersed phase, and rheological behavior with respect to parameters as temperature and/or water cut. Here, we present pulsed field Grgdient NMR methods that improve the performance as compared to existing methods. In particular, the so-called multi-echo approach is introduced to enhance the signal-to-noise ratio significantly making it possible to characterize emulsions in a minute or less. Thus, any evolution that takes place in the order of just a few minutes can be monitored. In addition to the multi-echo approach, an improved method for determining the droplet size distribution from a residual emulsion, i.e., in the presence of a bulk water phase, is presented.

Free fatty acids and their esters modulate isothermal crystallization of anhydrous milk fat

The effect of free fatty acids with different chain lengths or unsaturation degree on anhydrous milk fat (AMF) crystallization was evaluated. The impact of esterification was also studied using three triglycerides. Melted blends containing the additives at concentrations lower than 12wt.% were quenched at 25°C and isothermal crystallization was monitored by pulsed low-resolution nuclear magnetic resonance. In parallel, polarized light microscopy was used to observe the microstructure. Compounds based on long chain saturated fatty acids, i.e. palmitic, stearic, eicosanoic acids, tripalmitin and tristearin accelerated crystallization. Conversely, propanoic, hexanoic and oleic acids slowed down the process, while triacetin had no impact. Interestingly, above a critical concentration, the addition of palmitic, stearic or eicosanoic acids caused a transition from a one-step to two-step process. Gompertz model was used to fit the experimental data and to assess the influence of the molecular properties of the additives on the kinetic parameters.

Calibration of NMR Spectroscopy for Accurate Estimation of Oil Content in Sunflower, Safflower and Castor Seeds

Oil content analysis in oilseed crops requires methods that are non-destructive, accurate, fast, eco-friendly (without the use of solvent), inexpensive in terms of consumables, and easy to use. Pulsed low-resolution nuclear magnetic resonance (NMR) satisfies all these conditions. The objective of the present study was to develop an oil measurement method for seeds using NMR spectrometry. A bench-top pulsed NMR analyser was calibrated with respect to temperature. Six genotypes each of sunflower, safflower and castor were used for the analysis. Changes in sample conditioning temperature can lead to significant changes in the calibration graph. Based on the statistical parameters (correlation coefficient, variance and standard deviation) obtained, the best calibration was found for sunflower and safflower at 40°C and castor at 44°C among the temperature ranges tested.

Chicken Breast Meat Marinated with Increasing Levels of Sodium Bicarbonate

The aim of this study was to test the effect of different sodium bicarbonate concentrations on marination performances and meat quality properties. A total of 203 samples were obtained from an homogenous batch of 24 h post mortem chicken breast meat and were subjected to vacuum tumbling in a sodium chloride solution (1.0% wt/w in final product), containing 7 different sodium bicarbonate concentrations from 0 to 0.5%. Meat pH after marination linearly responded with about 0.17 pH unit increase per 0.1% unit addition of bicarbonate. The largest marinade uptake (11.4%) was observed in samples tumbled with 0.30% bicarbonate solution, while the uptake was levelled off, thereafter higher concentrations (0.40 and 0.50%). Cook loss showed a decreasing trend with the increase of bicarbonate level by estimating a 1.8% decrease for 0.10% of bicarbonate addition. Overall appearance of meat was not changed, while the use of sodium bicarbonate was able to improve meat texture by decreasing hardness and chewiness. By using low-resolution Nuclear Magnetic Resonance (LR-NMR) analysis, it was observed that water seemed to exert a plasticizing effect on some biopolymers, so that the total LR-NMR signal fluctuations were not always proportional to the water adsorption. Finally, water gain following marination does not correspond to an increase in the freezable water amount, as detected by differential scanning calorimetry. In conclusion, this study showed that sodium bicarbonate is a superior marinating agent and greater marination performances are obtained when using a concentration no higher than 0.3%.

Laplace inversion of low‐resolution NMR relaxometry data using sparse representation methods

Low-resolution nuclear magnetic resonance (LR-NMR) relaxometry is a powerful tool that can be harnessed for characterizing constituents in complex materials. Conversion of the relaxation signal into a continuous distribution of relaxation components is an ill-posed inverse Laplace transform problem. The most common numerical method implemented today for dealing with this kind of problem is based on L2-norm regularization. However, sparse representation methods via L1 regularization and convex optimization are a relatively new approach for effective analysis and processing of digital images and signals. In this article, a numerical optimization method for analyzing LR-NMR data by including non-negativity constraints and L1 regularization and by applying a convex optimization solver PDCO, a primal-dual interior method for convex objectives, that allows general linear constraints to be treated as linear operators is presented. The integrated approach includes validation of analyses by simulations, testing repeatability of experiments, and validation of the model and its statistical assumptions. The proposed method provides better resolved and more accurate solutions when compared with those suggested by existing tools. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 72–88, 2013.

Bringing it all together

Bringing it all together

Simple mobile single-sided NMR apparatus with a relatively homogeneous B0 distribution

This work presents a simple design for a mobile single-sided nuclear magnetic resonance (NMR) apparatus with a relatively homogeneous static magnetic field ( B 0) distribution. In the proposed design, the B 0 magnetic field of the apparatus is synthesized using only two permanent magnet blocks, i.e., a cube (main) magnet and a small shim magnet placed above the main magnet. The magnetic flux of the shim magnet partially cancels out that of the main magnet, subsequently creating a smooth B 0 profile above the shim magnet where low-resolution NMR experiments are performed. Compared with many previously published designs, this straightforward design simplifies the construction of the apparatus and simultaneously generates a B 0 field parallel to the apparatus surface, allowing the use of a simple loop-type radiofrequency (RF) coil. Additionally, an apparatus prototype is constructed according to the proposed design. Weighing only 1.8 kg, the constructed apparatus has a compact structure and can be held in the palm of a hand. The apparatus generates a B 0 strength of about 0.0746 T. Within a B 0 field deviation of 3 mT, the region with a relatively homogeneous B 0 distribution extends to about 11 mm above the shim magnet. The proposed apparatus can detect a clear Hahn echo or Carr–Purcell–Meiboom–Gill (CPMG) echoes of a pencil eraser block or a bottle of oil placed on the apparatus in 5 s with signal averaging using an RF transmitter power of only 19 W; the detection range of the apparatus exceeds 6 mm. The strength of the residual static magnetic field gradient of the apparatus is roughly estimated at 0.58 T/m. Applying different CPMG echo spacings in this residual static gradient leads to various transverse relaxation time ( T 2) contrasts for liquids with distinct viscosities such as water and oil. Two nondestructive inspection applications of the apparatus, including correlating the concentrations of magnetic nanoparticle solutions with their measured transverse relaxation rates ( R 2) and monitoring the outgassing from an opened bottle of oxygen-supersaturated water by measuring its longitudinal relaxation rate ( R 1), are also demonstrated.

Caking characteristics and sensory attributes of ramen soup powder evaluated using a low-resolution proton NMR technique

A low-resolution proton nuclear magnetic resonance (NMR) technique was used to characterize the quality of ramen soup powder during storage. The caking behavior of ramen soup powders was observed during 20 weeks of storage at different temperatures (30, 37, 45, and 55 °C) by monitoring changes in spin–spin relaxation times ( T 2) using a CPMG (Carr–Purcell–Meiboom–Gill) pulse sequence. Water in ramen soup powder was classified into two fractions based on two spin–spin relaxation times, T 21 and T 22, and their respective proton intensities, A 1 and A 2. Increases in T 21 and T 22 were observed during storage at 37, 45, and 55 °C, which indicated that the molecular mobility of water in ramen soup powder increased. The changes in A 1 and A 2 suggested that there was a redistribution of water from a lesser “bound” water state to more mobile state during storage. T 21 and A 1 were critical factors for explaining the caking characteristic of ramen soup powder during storage. Also, the results showed that sensory attributes of ramen soup powder deteriorated during storage, indicating that caking could accompany changes in organoleptic qualities and that these changes could be detected by monitoring changes in NMR parameters.

Olive oil content prediction models based on image processing

An increase in olive oil content in harvested olives can be achieved by optimizing the harvest time. In order to determine optimal harvest time, prediction models were developed to determine oil content based on quality features derived from known image processing algorithms. Digital colour photographs were taken weekly of opposite sides of large samples of Picual and Souri olives during the ripening season. In addition, the fallout was collected and weighed weekly during the same period. Quality features such as size, shape, colour, and texture were derived from the photographic images of the olives. Low resolution nuclear magnetic resonance was used for rapid and accurate determination of the oil content of each photographed olive. The correlations between the various quality features and oil content were determined. Two prediction models based on linear regressions and artificial neural networks were developed to predict the quantity of oil. The sensitivity of the models to the quality characteristics, different proportions between training and testing sets, the topologies of the networks, and various transfer functions were analyzed. Based on factor analysis, the characteristics that most strongly affect oil quantity for both varieties were found to be colour, texture, size, and shape. The neural network models were more accurate than linear regression, resulting in average linear correlations of 0.81 and 0.87 to the oil quantity in Picual and Souri olives, respectively. Improved results were obtained when features from images of both sides of the olives were considered. It is recommended to develop a specific model for each olive variety.

A Convenient Low-Resolution NMR Method for the Determination of the Molecular Weight of Soybean Oil-Based Polymers

By studying a series of soybean oil-based polymers, using low-resolution nuclear magnetic resonance (NMR) spectroscopy, an easy method to estimate molecular weight (MW) was developed. The relationship between a polymer's MW and the instrument's response can be correlated in a linear relationship. Correlation constants ( R 2 ) of 0.988, when data were taken at −10°C, and 0.999, when the study was done at 0 °C, were observed. Overall, this method is simple and with instrument modification, could be applied to other types of polymers as well.

Two-dimensional longitudinal and transverse relaxation time correlation as a low-resolution nuclear magnetic resonance characterization of ancient ceramics

Longitudinal and transverse relaxation time correlation (T1-T2) is employed as a nuclear magnetic resonance noninvasive characterization tool for archeological ceramics. This paper is aimed at investigating whether the most relevant firing-induced changes in ceramics, including those involving pore space properties and paramagnetic mineral structures, could be used as markers of the firing process and therefore of ceramics themselves. Ancient ceramics are made up of naturally available clays, often rich in iron impurities, which undergo relevant modifications of pore distribution upon firing. The firing process also assists chemical and physical rearrangement of iron-bearing species, yielding mineral structures with different magnetic properties. That being so, T1-T2 maps are expected to show the interdependence between ceramic structure and firing technology. T1 and T2 distributions are basically proportional to pore-size distribution, but T2, which is also sensitive to magnetic susceptibility effects, may give information on the porous matrix composition as well. Such a methodology has first been employed on laboratory-prepared ceramic samples, with different paramagnetic compositions and controlled firing temperatures, in order to tackle the problem of model-ceramic selection. Then, the T1-T2 correlation approach has been used on medieval ceramic findings in order to get information about their thermal and compositional history. The information obtained by means of two-dimensional correlation maps proves coherent with archeological dating, thus illustrating the capabilities of this method.

Nuclear magnetic resonance characterization of metabolite disorder in orange trees caused by citrus sudden death disease

Citrus sudden death (CSD) is a new disease of sweet orange and mandarin trees grafted on Rangpur lime and Citrus volkameriana rootstocks. It was first seen in Brazil in 1999, and has since been detected in more than four million trees. The CSD causal agent is unknown and the current hypothesis involves a virus similar to Citrus tristeza virus or a new virus named Citrus sudden death-associated virus. CSD symptoms include generalized foliar discoloration, defoliation and root death, and, in most cases, it can cause tree death. One of the unique characteristics of CSD disease is the presence of a yellow stain in the rootstock bark near the bud union. This region also undergoes profound anatomical changes. In this study, we analyse the metabolic disorder caused by CSD in the bark of sweet orange grafted on Rangpur lime by nuclear magnetic resonance (NMR) spectroscopy and imaging. The imaging results show the presence of a large amount of non-functional phloem in the rootstock bark of affected plants. The spectroscopic analysis shows a high content of triacylglyceride and sucrose, which may be related to phloem blockage close to the bud union. We also propose that, without knowing the causal CSD agent, the determination of oil content in rootstock bark by low-resolution NMR can be used as a complementary method for CSD diagnosis, screening about 300 samples per hour.

High-throughput non-destructive nuclear magnetic resonance method to measure intramuscular fat content in beef

High intake of saturated fat from meats has been associated with cardiovascular disease, cancer, diabetes, and others diseases. In this paper, we are introducing a simple, high-throughput, and non-destructive low-resolution nuclear magnetic resonance method that has the potential to analyze the intramuscular fat content (IMF) in more than 1,000 beef portions per hour. The results can be used in nutritional fact labels, replacing the currently used average value. The method is based on longitudinal (T(1)) and transverse (T(2)) relaxation time information obtained by a continuous wave-free precession (CWFP) sequence. CWFP yields a higher correlation coefficient (r = 0.9) than the conventional Carr-Purcell-Meiboom-Gill (CPMG) method (r = -0.25) for IMF in beef and is just as fast and a simpler pulse sequence than CPMG. The method can also be applied to other meat products.

Low- and high-resolution nuclear magnetic resonance (NMR) characterisation of hyaluronan-based native and sulfated hydrogels

Hyaluronan-based hydrogels were synthesised using different crosslinking agents, such as 1,3-diaminopropane (1,3-DAP) and 1,6-diaminohexane (1,6-DAE). The hydrogels were sulfated to provide materials (Hyal-1,3-DAP, Hyal-1,6-DAE, HyalS-1,3-DAP and HyalS-1,6-DAE) that were characterised by both high- and low-resolution nuclear magnetic resonance (NMR) spectroscopy. The 13C NMR spectra of the materials were analysed to identify, characterise and study the crosslinking degree of the hydrogels. The crosslinking degree was also determined by potentiometric titration and the effectiveness of the two techniques was compared. Measurements of longitudinal relaxation times (spin–lattice) and of NOE enhancement were used to study the mobility of the hydrogels. Low-resolution NMR studies allowed the determination of the water transport properties in the hydrogels. In addition, the swelling degree for the various hydrogels was calculated as a function of the longitudinal and transversal relaxation times of the water molecules. Lastly, the self-diffusion coefficients of the water in interaction with the four polysaccharides were measured by the pulsed field gradient spin echo (PFGSE) sequence.

A low-resolution and high-resolution nuclear magnetic resonance integrated approach to investigate the physical structure and metabolic profile of Mozzarella di Bufala Campana cheese

A low-resolution and high-resolution nuclear magnetic resonance (NMR) protocol to characterise the traditional Italian cheese Mozzarella di Bufala Campana is reported. Low-resolution relaxometry was used for the study of the state and distribution of water in different structural elements of cheese resulting from the stretching process. High-resolution NMR allowed definition of the “chemical fingerprint”, the cheese complex matrix profile of low molecular weight metabolites extracted from Mozzarella. Both low-resolution and high-resolution NMR seem to provide useful parameters that could be used for monitoring the evolution of PDO (protected destination of origin) Mozzarella di Bufala Campana cheese.

Influence of the season on the relationships between NMR transverse relaxation data and water‐holding capacity of turkey breast meat

AbstractIn the last few years the poultry industry has seen a significant deterioration in meat quality properties during the summer season. The objective of this study was to evaluate the seasonal effect (summer and winter) on turkey meat quality assessed by both conventional and low‐resolution nuclear magnetic resonance (LR‐NMR) analysis. Eighty‐eight breast muscle samples (35 winter and 53 summer) from BUT‐Big 6 turkeys belonging to 16 different flocks, were randomly collected from a commercial processing plant. The samples were analysed for transverse relaxation times (T2) by LR‐NMR and for initial pH (15 min post mortem), ultimate pH (24 h post mortem) and pH after cooking, temperature at 15 min post mortem, water‐holding capacity (WHC, drip loss, filter paper press wetness and cooking loss) at 24 h post mortem, colour of raw and cooked meat and chemical composition (moisture, lipids and proteins). The results indicate that, during the summer season, turkey breast meat undergoes a relevant WHC decrease. Cluster analysis of the raw LR‐NMR data evidenced the presence of two groups corresponding to samples harvested in each different season. Correlations between the LR‐NMR signal and the conventional parameters measuring WHC were obtained by a recently proposed type of principal component regression (PCR) termed relative standard deviation PCR. Copyright © 2004 Society of Chemical Industry

Characterisation of different treated whey protein concentrates by means of low-resolution nuclear magnetic resonance

Abstract In order to slow down the evolution and to minimise the extent of syneresis in dairy products the effect of new process steps and recipes on the structure of the final products were studied. The objective of this paper was to detect structural changes with regard to the water-immobilisation of differently treated whey protein concentrates (WPC) by means of nuclear magnetic resonance (NMR). The first measurements with pure WPC show obvious variations for the differently treated samples and the original native sample (a). (b) Denatured and (c) denatured and additionally sheared WPCs show not only an observably higher viscosity, but also shorter relaxation times. The fraction of the immobilised phase is about twice as high as in native WPC samples. These data reveal an improved water-holding capacity. (d) WPC samples mixed with cream and afterwards emulsified show a different behaviour with regard to their water-holding capacity during the evolution of the shearing process. The results suggest that for each treatment and/or change of the recipe the optimal shearing time has to be determined in order to achieve minimal relaxation times. These are obviously correlated with the highest water-holding capacity. The presented data indicate that NMR measurements are a useful technique to detect and analyse changes of the mobility of water and to identify fractions of differently bound/immobilised water phases of WPCs in dependence on the corresponding pre-treatment and recipe, respectively.

Characterisation of the water-holding capacity of fresh cheese samples by means of low resolution nuclear magnetic resonance

New process steps in the production of fresh cheese were introduced and varied in order to reduce the undesirable phenomenon of syneresis without adding milk-foreign additives. Native and modified whey protein concentrates (WPC) with approx. 12% protein were used as ingredients in the production of fresh cheese spreads. During production the fresh cheese samples were submitted to an extra flow-induced mechanical stress. The aim of the present study is to detect changes of the water-holding capacity of different treated fresh cheese by means of the non-destructive low resolution nuclear magnetic resonance (LR NMR). Furthermore, a newly developed measuring method based on NMR, the so-called wash-out-test, was implemented in order to simulate syneresis of fresh cheese. The obtained data were correlated with the results of the viscosity and the firmness of the samples. Syneresis data were determined by decanting experiments as a function of the storage duration. The present study shows that the shearing procedure during processing has an influence on the viscosity of the final product, its firmness and the syneresis behaviour of the fresh cheese samples. The main result is that good syneresis properties seem to be correlated with a softer mechanical consistency of the products. The presented data indicate that NMR measurements and, especially, wash-out-tests are useful techniques to characterise the water-holding capacity (WHC) and the structure of differently treated fresh cheese samples. Based on this knowledge concerning the microscopic and macroscopic material behaviour, it is possible to improve the production processing and the final, consumer-relevant properties of fresh cheese products.

Continuous wave free precession: Practical analytical tool for low-resolution nuclear magnetic resonance measurements

The use of continuous wave free precession (CWFP) as a practical analytical tool for quantitative determinations in low-resolution nuclear magnetic resonance (LRNMR) is examined. The requirements of this technique are shown to be no more demanding than those prevailing in free-induction decay or spin-echo measurements. It is shown that the substantial gain in signal to noise ratio for a given acquisition time permitted by CWFP, can be exploited with advantage in practically any application of LRNMR. This applies not only to homogeneous low viscosity liquid samples but also to multi-component systems where differences in relaxation times of each component permit a separation of the individual contributions. As an example, the use of CWFP for fast quantitative determination of oil and moisture in various seeds is presented.

Stray Field Nuclear Magnetic Resonance of Soil Water

Development, characterization, and preliminary results of a recent technique capable of local measurements of pore-size distribution by a spatially resolved low resolution nuclear magnetic resonance (NMR) technique are described. Potential environmental uses include studying the change in pore-size distribution caused by surface compaction, which influences surface runoff, and obtaining information on the physical state of non-aqueous compounds in porous materials, which should aid the selection of appropriate soil remediation methods. Stray field (STRAFI) imaging is an NMR technique that allows distortion-free imaging of materials with short NMR relaxation times. The sample is placed in the strong axial fringe field gradient of a superconducting NMR magnet. We report on a new, unique, large 5-cm-diameter STRAFI probe, and its use for three preliminary test cases: water in ceramics of known pore size, paraffin wax and oil in sandstone rock, and water in soil at different matric potentials. The imaging is confined to one dimension with a spatial resolution of the order of 100 microm for protons. The optimum position for imaging occurs at 2.62 T and a gradient of 12.1 T/m. Water relaxation decay curves can be measured at any position in the 8-cm-long sample. These curves are decomposed into a series of terms each corresponding to a different pore size. Preliminary results show continuum fits to decay curves for a soil drained to three different matric potentials. Such information will be useful for interpreting water retention curves and will lead to understanding of the behavior of fluids in the vadose zone.