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Nuclear magnetic resonance (NMR) is a versatile technique that allows assessing the composition and structure of food samples. It provides information on molecular properties, which can be used for quantification of concentration and interactions of components within the food samples. Due to the fact that many foods are proton-rich (with protons originating from water, fat, carbohydrates, and proteins) and carbon-rich (originating from fat, carbohydrates, and proteins), 1H and 13C NMR have become the most common type of NMR in food analysis.1-3 NMR is used in a wide range of applications, included in the fields of food microbiology, food chemistry, food engineering and food packaging (see Table 1)4-23. Table 1 shows the multiple applications of NMR in food science. Analysis of food components is nowadays one of the main interests of authors. Water, proteins, and fat have been studied qualitatively, and in some cases, also quantitatively. Other aspects, such as processing, conformational analysis of certain molecules, and packaging, are also among the targets. In case of quality control, NMR is valued to certificate the quality of highly appreciated food products for consumers, for instance, olive oil. Within the field of food process engineering, two water-in-food issues widely studied with NMR techniques are the translation and location of water in food samples, as well as water-biopolymers interactions.24-27 Within all types of NMR, time domain nuclear magnetic resonance (TD-NMR) turns out to be a fast and accessible tool to study water populations present in food. Most of the TD-NMR studies on food samples use relaxometry methods. Spectral information seems to provide less information for water-related issues because water present in various physical environments does not give chemical differences (e.g., chemical shifts). The reason is that water is found in various physical environments, but chemical differences barely exist.26 The relaxometry analyses are based on differences in transverse relaxation times (the so-called T2, or its inverse R2 = 1/T2) of components. T2 values for water in food depend on the concentration of water in the food matrix, and usually range from microseconds to seconds. These T2 values can therefore be related to different populations of protons (1H) with various rotational mobilities, which can then be assigned to different groups of proton-bearing water populations contained in a proteinaceous sample.4, 26 The objective of this perspectives paper is, first, to collect studies on water binding to proteins and their interactions within proteinaceous food samples. Then, perspectives of future work on this topic are presented. In order to study water population within samples, Dekkers et al. (4) associated transverse relaxation times on the TD-NMR spectrum to proton-bearing components. As shown in Figure 1, the transverse decay curves were analysed with the Levenberge-Marquardt non-linear least squares algorithm. This algorithm fits a sum of exponential curves—the so-called components—to the decay, resulting in an amplitude A and transverse relaxation time T2 for each component. The longest relaxation time of the sample in the spectrum, which is shorter than that of pure water, would correspond to some relatively mobile water within interstices in the protein matrix. The fact that this relaxation time is lower than that of free water, in their conclusion, may be due to pore confinement and by fast proton exchange with dissolved components. When the concentration of soy protein isolate (SPI) rises, this water population disappears, which suggests stronger water-binding capacity of SPI at this concentration. The relaxation time of the averaged middle two components represented more than 90% of the signal intensity. This signal was assigned to absorbed water. The T2 of this water population decreases as a function of protein concentration, reflecting the decreasing mobility of this fraction. Finally, the component with the shortest relaxation time probably represents protein-bound protons. The intensity of this signal rises with concentration, which leads to think that it could represent the protein-bound proton population. The slight dispersion of relaxation rates of the middle fraction—which corresponds to second and third water populations, averaged on this spectrum—may be due to the heterogeneity within the individual phases. Another example of information that can be extracted from TD-NMR studies on water is the compared study of water-binding capacity (WBC) of different materials. Figure 2 shows the comparative study of four plant-based materials carried out by Peters et al.6. It can be observed that vital wheat gluten calibration curve increased more gradually than was found for SPI, pea protein isolate, and lupin protein concentrate. This behaviour might be explained as being related to isoelectric point of the proteins. The isoelectric point of gluten is around 7.5—whereas the value for the other proteins is around 4.5—which would lead gluten to less interact with water in these samples.28 Dekkers et al.5 focused on the WBC of phases in a blend of plant-based materials in order to better understand the rheological behaviour of that blend. The blend consisted of a phase-separated blend of an aqueous SPI phase and aqueous Wheat Gluten (WG) phase. The exact distribution of water over both phases determines the blend rheological properties. In past studies on rheology of biopolymer blends, the water distribution was often taken as a fit parameter. Now, NMR was used to determine the water distribution quantitatively, and the outcomes of NMR turned out to be fully in line with water distributions as predicted by rheology. The authors calculated a theoretical R2 value of water distributions in SPI-WG blends, then compared these values with experimental R2 values of the blends. They observed that experimental R2 values were lower than the calculated R2 values, which would mean that water was more mobile than expected. This could be explained by the fact that water was not evenly distributed among the SPI and WG phases. Peters et al.8 studied a dairy material for its WBC as well. They compared measurements of WBC on whey protein pellets by weighing the pellet obtained after centrifuging a dispersion with TD-NMR measurements. Previously, it was assumed that the interstitial water (water between particles) can be neglected, implying that all water was absorbed by dry matter in the pellet. However, this assumption turns out to be inaccurate to measure WBC. As a matter of fact, TD-NMR did allow differentiation between water inside and between the particles, which leads to a more accurate assessment of different populations of water inside the food sample. Figure 3 shows how TD-NMR can be potentially useful to study WBC in food samples. As stated in the introduction, a need exists for developing a new category of product, being dense protein food products. Partly as healthy foods,29 partly as products that can replace products from animal origin. A key element of interest is to better understand the sensory properties of those products. High-protein foods are often associated with hard and dry texture. Furthermore, plant-based products are often less juicy than the animal-based ones. TD-NMR is an attractive tool to investigate water binding in dense protein products. It allows to differentiate the different water populations in a product as well as to quantify them. Thus, a simple but versatile tool is available to compare differences in water binding of various products. We can therefore imagine that future research will focus TD-NMR studies on a broad range of samples, including plant-based food samples. For this purpose, both classic ingredients (soybean, lupin, wheat gluten) as well as novel plant-based ingredients (rapeseed, sunflower, pea, faba bean) will be studied. The first objective will be to identify water populations within the samples and their dependence with certain parameters, such as dry matter content, pH, or amount of added salt. Certain stages of processing, such as heating or shearing, can be included as well. A further step would be to compare the relative TD-NMR signals to carry out semi-quantification. Finally, we will aim to quantify these water populations in absolute units. The second objective will be the study of the biopolymers, which constitute the food matrix, these include fat, proteins, and carbohydrates as well as the interactions amongst them. Fat content determination is nowadays labour-intensive and invasive, thus a faster and non-invasive alternative is highly desirable. Both identification and quantification of these biopolymers will be aimed.
5Molecular mobility changes after high-temperature, short-time pasteurization: An extended time-domain nuclear magnetic resonance screening of ewe milk
Molecular mobility changes after high-temperature, short-time pasteurization: An extended time-domain nuclear magnetic resonance screening of ewe milk
Read more17Physical characterization of high methoxyl pectin and sunflower oil wax emulsions: A low-field 1 H NMR relaxometry study.
Pectin-wax-based emulsion systems could be used to form edible films and coatings with desired water permeability characteristics. Pectin is often used in food industry due to its gelling and viscosity increasing properties. Physical properties of pectin are highly dependent on its esterification degree. Waxes are commonly used as edible coatings to enhance the water barrier properties of food products. This study focuses on preparing emulsions with sunflower oil wax (SFW) and high methoxyl pectin (HMP) at different concentrations for any possible edible film or coating formulations. Sunflower oil (SFO) was added as the dispersed oil phase to these emulsions. Characterization of the emulsions was performed by using particle size, rheology, and time domain nuclear magnetic resonance (NMR) relaxometry measurements. Effects of HMP concentration and the presence of SFO in the emulsion formulations were explored. Mean particle size values were recorded between 1 and 3µm. Rheology measurements showed that increasing HMP concentrations and presence of SFO in emulsions resulted in more pseudoplastic behavior. NMR transverse relaxation times (T2 ) were measured to detect the differences between the emulsions. Relaxation spectrum analysis was also conducted for a detailed understanding of the transverse relaxations. Addition of SFO and higher HMP concentrations decreased the T 2 values of the emulsion systems (P<0.05). However, T2 decreasing effect of SFO was compensated at 10% (w/w) HMP concentration showing that SFO was well dispersed in this particular emulsion formulation. Changes in the rheological behavior and relaxation times provided insight on the formation and stability of the emulsions. PRACTICAL APPLICATION: Findings of this study can be utilized and integrated to produce edible films and coatings with different water permeability characteristics. This study showed that NMR relaxometry parameters were also effective in monitoring and determining the physical characteristics of the pectin-wax-based emulsion systems as other conventional techniques including rheology and particle size measurements. Our NMR relaxometry findings were in correlation with the flow behavior and particle size results of the investigated emulsion systems.
Read more361H NMR Relaxation Study to Evaluate the Crystalline State of Active Pharmaceutical Ingredients Containing Solid Dosage Forms Using Time Domain NMR
1H NMR Relaxation Study to Evaluate the Crystalline State of Active Pharmaceutical Ingredients Containing Solid Dosage Forms Using Time Domain NMR
Read more9Quantitative evaluation of adsorption behavior of carboxymethylcellulose on carbon nanotubes by time-domain NMR with the aim of obtaining stable dispersions
Quantitative evaluation of adsorption behavior of carboxymethylcellulose on carbon nanotubes by time-domain NMR with the aim of obtaining stable dispersions
Read more24Interfacial moduli at large strains and stability of emulsions stabilised by plant proteins at high bulk shear rates
For several commercial plant-protein stabilisers, we investigated how surface shear and dilatational properties affect dynamic emulsion stability under high bulk shear conditions. Potato protein isolates Potato-1 (rich in patatin) and Potato-2 (rich in protease inhibitors) showed a stiffer, more solid-like response than soy and pea protein isolates in large amplitude oscillatory surface shear. Soy protein isolates had the weakest interfaces and showed a more liquid-like behaviour. Potato-2 had the highest stiffness and most brittle interface in large amplitude oscillatory dilatational deformations. It also showed more significant softening, evident from both the shear and dilatational Lissajous plots. Only the Potato-1-stabilised emulsion was stable against coalescence at high bulk shear (although that emulsion was unstable against flocculation because of its low zeta potential). The low stiffness imparted to the interface by the pea and soy protein isolates was not suitable for preparing emulsions with high dynamic stability. In the linear regime, both Potato-1 and Potato-2 produced interfaces with similar surface shear moduli, and in dilatation, Potato-2 gave a higher modulus. The lower stability of the Potato-2 emulsions appears to be linked to the higher brittleness and stronger softening effect for increasing deformation amplitude. Both in surface shear and dilatation, the maximum linear strain for the Potato-1-stabilised interface is larger. The lower maximum linear strain and stronger softening effect at high deformations for Potato-2 may have resulted in more disruption of the interfacial microstructure, and this induced (partial) coalescence.
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1A straightforward method for disaccharide characterization by a simplified version of time domain nuclear magnetic resonance
The necessity of identifying and quantifying sugars in food processing is endless for maintaining food quality attributes such as color, taste, and texture, monitoring regulatory compliance, labeling packages, and maintaining authenticity. Despite available analytical methods for characterizing sugar molecules, the limitations of conventional methods drive researchers to seek more convenient alternatives. This study aimed to characterize common disaccharides such as saccharose, lactose, maltose, and trehalose using a simplified version of time domain nuclear magnetic resonance (TD-NMR), facilitating a quick, cost-effective, and user-friendly approach. In the transverse relaxometry, secondary peak(s) were observed for all the disaccharides with a main peak. Although they have similar molecular formulas and weights, lactose exhibited the longest relaxation time for the secondary peak, followed by trehalose, saccharose, and maltose. This behavior was assumed due to the interaction of sugar molecules with water. The increasing concentration of disaccharide in the solution displayed the leftward shifting of peaks. Maltose showed two secondary peaks, which were not observed in other sugar samples. This TD-NMR showed potential to distinguish disaccharides from unknown powders and solutions by analyzing either the relaxation time of the secondary peak or the ratio of the secondary to the total peak. Moreover, quantification is possible from the standard curves of relaxation time and the combined surface area of the main and secondary peaks with the corresponding sugar concentration. However, it shows challenges in discrimination between α- and β-isomers.
Read more228Investigation on water status and distribution in broccoli and the effects of drying on water status using NMR and MRI methods
Investigation on water status and distribution in broccoli and the effects of drying on water status using NMR and MRI methods
Read moreResearch on Soluble Protein Surface Hydrophobicity of Biomaterial Solution from Soy Protein Isolate - Polysaccharide System
The work attempts to study the surface hydrophobicity (S0) of soy protein isolate（SPI）-guar gum(GG) systems for biomaterial. Effect of four factors on the S0 values of the mixtures were studied. A response surface analysis was carried out using the Box-Behnken Design (BBD)method in order to determine the effects and interactions of pH (6.0, 8.0, 10.0), salt(0.05, 0.15, 0.25M), guar gum(0.10, 0.30, 0.50% w/v) and SPI concentrations (3, 4, 5% w/v) on the S0 values of mixtures. The datas were fitted into second order quadratic model. Salt concentration, pH and SPI concentration, interactions between pH and salt concentration, pH and GG concentration, pH and SPI concentration, GG and SPI concentrations were significant(P<0.05).
Read more2A nuclear magnetic resonance advance. Imaging fluorinated anesthetics in the brain.
A nuclear magnetic resonance advance. Imaging fluorinated anesthetics in the brain.
36Rapid and simple determination of [formula omitted] relaxation times in time-domain NMR by Continuous Wave Free Precession sequence
Rapid and simple determination of [formula omitted] relaxation times in time-domain NMR by Continuous Wave Free Precession sequence
Read more15Optimizing foam quality characteristics of model food using Taguchi‐based fuzzy logic method
In this study, the effects of soy protein isolate (SPI) concentration (0%, 50%, and 100%), sonication time (10, 20, and 30 min), and whipping time (5, 10, and 15 min) on the quality characteristics of the model food foam were investigated and optimized. In order to maximize both foaming capacity (FC) and foam stability (FS), it was aimed to select the optimum process parameters using a Taguchi‐based fuzzy logic method (TBFLM). The experiments were performed according to Taguchi L9 (33) orthogonal design, and the effects of process parameters on foam quality characteristics were investigated by analysis of variance. Optimization results revealed that optimum FC and FS values were obtained with 50% SPI, 30 min sonication, and 10 min whipping. SPI concentration was the most effective factor for the responses in Taguchi single‐response optimization. However, the whipping time has the greatest impact on the multiperformance characteristics index, accounting for 78.93% of the contribution to fuzzy logic multiresponse optimization. The verification experiments revealed that the TBFLM is a useful method for improving foam quality characteristics.Practical applicationsFC and FS are the most important properties, which represent the quality characteristics of model food foams. The Taguchi method failed in multiresponse optimization in the model food application. A Taguchi‐based Fuzzy logic optimization method was successfully applied to optimize the quality characteristics of model food foam, and the optimal conditions were determined as soy protein isolate of 50%, sonication time of 30 min, and whipping time of 10 min. The contribution of whipping time to the multiperformance characteristics index was found to be the highest.
Read more3Comparison of the effect of soy protein isolate concentration on emulsion stability in the absence or presence of monoglyceride
Comparison of the effect of soy protein isolate concentration on emulsion stability in the absence or presence of monoglyceride
Read more8Effect of Nonprotein Components for Lipid Oxidation in Emulsions Stabilized by Plant Protein Extracts.
Plant protein ingredients are rich in non-protein components of which the antioxidant and pro-oxidant effects are expected to be considerable. In this paper, commercial soy and pea protein isolates and concentrates were selected by using their soluble fractions to prepare oil-in-water (O/W) emulsions. Emulsions stabilized with soy protein isolates were more prone to lipid oxidation than those with soy protein concentrate or pea protein isolate. Compositional analysis revealed that the soluble fraction of soy protein isolates contained higher concentrations of phenolic compounds and metals (iron and copper) but lower mineral and ash contents than those of soy protein concentrate and pea protein isolate. Correlating the composition to oxidation in emulsions highlighted the significant role of non-protein components, alongside the protein's oxidative state. These findings are relevant for the use of alternative proteins in food formulation, a practice often promoted as sustainable yet that may come with repercussions for oxidative stability.
Read more101Functional properties of fermented milk produced with plant proteins
Functional properties of fermented milk produced with plant proteins
12A method based on time domain nuclear magnetic resonance for the forensic differentiation of latex gloves
Latex gloves are employed by felons who want to avoid shedding fingermarks or biological traces, and are sometimes discarded on the crime scene or nearby. Comparison between the gloves found at the crime scene and those seized in the suspect's premises can provide useful information to investigators. This paper proposes the use of 1H time domain nuclear magnetic resonance (TD-NMR) as a method for performing such a comparison. Two parameters can be quantified by this technique: the proton weight fraction, which is correlated to the chemical nature and formulation of the material, and the relaxation time T2, which is a measure of polymer chain dynamics. Both these features can be ultimately associated to differences in raw materials, formulation and processing of the gloves, thereby offering a means to discriminate items which are indistinguishable by visual examination. TD-NMR, without sample preparation and preserving the integrity of the specimen, allows differentiating 88% of the possible pairs of samples in a population of 20 latex gloves. TD-NMR data are complementary to those coming from thermal analysis.
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