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Quality control with time‐domain NMR
Abstract
Cette etude detaille les applications de la RMN dans le domaine temps au controle qualite ainsi qu'a la Recherche et Developpement dans l'agro-alimentaire. Des normes internationales comme le contenu en graisse solide SFC et la determination de la teneur en huile et humidite sont evoquees. En outre, des applications plus pointues comme la determination des distributions de taille de gouttelettes dans des emulsions H/E et E/H sont presentees et comparees aux autres techniques d'analyse.
... The determination of the flavour oil concentration in delivery systems is a crucial aspect in both the development of new systems as well as in the quality control of industrially produced systems since the oil loading directly determines the performance of the final product. Non-subjective procedures and analytical instrumentation are therefore mandatory in the framework of good manufacturing practice, GMP [4]. A common technique for the determination of oil loading is time-domain NMR (TD-NMR). ...
... A common technique for the determination of oil loading is time-domain NMR (TD-NMR). Compared to classical analytical methods, for example solvent extraction, NMR provides several advantages, as the method is non-invasive, usually fast and requires minimal sample pre-treatment [4][5][6]. This technique is widely used in the food industry on relatively inexpensive benchtop NMR spectrometers for the assessment of the phase composition of lipid-based food products [7,8]. ...
... Samples were thermostatted at 308C for 30 min before the actual measurement and this temperature was kept constant throughout the measurement. The contribution of protons associated with the flavour oil to a TD-NMR signal can be separated from the solid matrix by means of a spin-echo sequence [4]. A 908 pulse length of 6.4 ms and a 1808 pulse length of 12.8 ms was applied, with a 90-1808 interpulse spacing t of 3.5 ms. ...
The determination of the flavour content of a newly developed encapsulation system based on yeast was attempted using time-domain NMR (TD-NMR) and compared to thermo gravimetric analysis (TGA). Flavour content as measured by TD-NMR is systematically higher than by TGA. The constant discrepancy between the two techniques is attributed to the presence of the phospholipidic membrane inside the yeast. These phospholipids also contribute to the NMR signal as was revealed by high field NMR studies under magic angle spinning conditions. The signal obtained for the empty yeast matched the extra-contribution to the signal of the flavoured yeast encapsulation system. A classical glassy encapsulation system was used as a comparison to highlight further the presence of the phospholipids in the yeast system. A two step procedure is proposed to correct the reading of the flavoured yeast for the contribution of the yeast cells themselves.
Practical applications: TD-NMR is routinely used for the determination of the liquid content encapsulated in a solid matrix, where the liquid can be any oil, including lipids, or flavour and fragrance oils. As shown in the present study, in order to obtain accurate values of the oil loading, the nature of the carrier material of the encapsulation system must be taken into account. For example, with the conventional TD-NMR method, flavour loading in encapsulation systems in yeast cells is systematically overestimated since the phospholipid bilayer contributes to the NMR signal of the flavour oil. With the two-step procedure presented in this article, by subtracting the baseline value obtained for empty yeast cells, accurate loading values for yeast cell carriers can be determined. The modified testing approach is highly accurate and widely applicable to a variety of liquids including flavours, perfumes or nutritive fish oils encapsulated in solid delivery systems.
... Meanwhile, time-domain nuclear magnetic resonance (TD-NMR) has aroused widespread interest for its use as a convenient method to quantitate lipid since it was introduced approximately 35 years ago (Todt et al., 2001). Compared with ordinary NMR, TD-NMR is faster, easier to use and less expensive. ...
... Compared with ordinary NMR, TD-NMR is faster, easier to use and less expensive. TD-NMR is based on the different relaxation times of hydrogen nuclei in different phases of the sample analyzed (Todt et al., 2001). The solids such as carbohydrate and protein exhibit the shortest relaxation times in the order of microseconds, whereas the relaxation times for bound water, free water and lipid are a few hundreds of microseconds, seconds and a few hundreds of milliseconds, respectively (Todt et al., 2006;Kenar, 2007). ...
... Lipid content can be determined after appropriate calibration. Lipid determination for seeds and seed residues with TD-NMR is recognized as International Standards Methods (ISO/CD 10632 for Oilseed Residues, 1993;ISO 10565 for Oilseeds, 1995), and the application of TD-NMR has been widened to polymer, agricultural and food industries (Rugraff et al., 1996;Todt et al., 2001;Sorlanda et al., 2004;Hickey et al., 2006). However, the use of TD-NMR for lipid determination in microorganism especially in microalgae has received little attention. ...
A specific strain of Chlorella protothecoides has been studied in heterotrophic fermentation for increasing cell growth rate and lipid content for biodiesel production. For optimizing the process of fermentation to reduce costs of alga-based biodiesel production, rapid determination of lipid content in microalgal cells is critical. Nile Red (NR) staining and time-domain nuclear magnetic resonance (TD-NMR) have been investigated to quantitate the lipid content in C. protothecoides. Both methods were found feasible and simpler than gravimetric methods that are commonly employed. The TD-NMR method showed better agreement (R(2)=0.9973) with the measured values from lipid extraction experiments than the NR staining method (R(2)=0.9067). Additionally, the smaller standard deviations of the samples (< or =0.36) analyzed by TD-NMR revealed that the method is accurate and reproducible. The application of TD-NMR for lipid quantitation in C. protothecoides opens up the possibility of determining lipid content in algal fermentation precisely and quickly.
... An alternative technique for lipid analysis is offered by Time-Domain Nuclear Magnetic Resonance (TD-NMR). This is widely employed in food characterization to quantify the solid fat, water and oil contents of foodstuffs based on well-known international standard methods (see references in Todt et al., 2001). TD-NMR works by applying a sequence of radiofrequency fields to a sample placed in a magnet to excite the molecule nuclei's magnetic moments and record their return to equilibrium after the radiofrequency pulse is switched off. ...
... The NMR-signal amplitudes or the differences in these relaxation constants are correlated to the physicochemical properties of the samples. For example, the relaxation behaviors of liquid and solid fat components differ, allowing their respective content values to be calculated (Todt et al., 2001). The main advantages of the TD-NMR technique over Soxhlet extraction lie in the former's speed and solvent-free nature. ...
Time-Domain Nuclear Magnetic Resonance (TD-NMR) was used to quantify the lipid contents of 48 different organic waste substrates. Results obtained from TD-NMR were compared to those from Soxhlet extraction, currently the prevalent method for organic waste characterization, especially in the field of anaerobic digestion. Two calibration methods were tested. The first was a self-calibration process using pure oils (NMR1) which showed good repeatability compared to Soxhlet extraction with a better coefficient of variation (5%). Analyses of volatile fatty acids (VFA) and long-chain fatty acids (LCFA) by chromatography were carried out to understand why the NMR1 method produced underestimations for some samples. Statistical analysis showed that the presence of saturated fatty acids had a significant effect on differences between the Soxhlet and NMR1 methods. The second calibration method applied chemometrics to TD-NMR raw data (NMR2), taking Soxhlet extraction values as references. It provided a good prediction of lipid content and avoided the lengthy calibration procedure usually required for this type of study. Last, the NMR2 method was shown to be highly suited to the quantification of lipids in organic waste, demonstrating better repeatability than the classic Soxhlet method.
... The fast and non-invasive methods to determine oil content in oilseeds were the first applications of time domain nuclear magnetic resonance (TD-NMR) in plant science, and they have since been used in germplasm evaluation and plant breeding programs [1]. The analyses of oilseeds, with low moisture content, are performed by measuring the intensity of free induction decay (FID) after a radiofrequency (rf) pulse. ...
... The CWFP regime is obtained when Tp is shorter than T2 and T2* (T2 >> Tp < T2*). In the CWFP regime ( Figure 6B,C) FID and echo signals are overlapped and the interaction is constructive (B) or destructive (C), depending on the precession angle = 0Tp (0 is the frequency offset from resonance), flip angle θ, and T1 and T2 relaxation times according to Equation (1). For Tp = 0.3 ms, θ = π/2, and = (2n+1) = 8.333 kHz, the interaction is constructive, yielding a CWFP signal with maximum amplitude ( Figure 6B). ...
Time domain nuclear magnetic resonance (TD–NMR) has been widely applied in plant science in the last four decades. Several TD–NMR instruments and methods have been developed for laboratory, green-house, and field studies. This mini-review focuses on the recent TD–NMR pulse sequences applied in plant science. One of the sequences measures the transverse relaxation time (T2) with minimal sample heating, using a lower refocusing flip angle and consequently lower specific absorption rate than that of conventional CPMG. Other sequences are based on a continuous wave free precession (CWFP) regime used to enhance the signal-to-noise ratio, to measure longitudinal (T1) and transverse relaxation time in a single shot experiment, and as alternative 2D pulse sequences to obtain T1–T2 and diffusion-T1 correlation maps. This review also presents some applications of these sequences in plant science.
... Time domain nuclear magnetic resonance spectroscopy (TD-NMR) has been widely used to obtain qualitative and quantitative information about food composition, structure and dynamic, in short experimental time, in non-destructive and non-invasive way, using minimal sample preparation and minimal or no chemical waste Duynhoven et al., 2010;Marcone et al., 2013;Todt et al., 2001). These analyses are based either on the measurements of free induction decay (FID) and echo amplitudes, or on the measurements of longitudinal (T 1 ) and transverse (T 2 ) relaxation time Duynhoven et al., 2010). ...
... The first commercial TD-NMR spectrometer was developed to replace cumbersome dilatometry methods for determination of solid fat content in fat and oil industry (Duynhoven et al., 2010). Nowadays, TD-NMR methods are widely used in agri-food industries in order to determine oil, fat and moisture content, solid fat content in fat blends, shelf-life stability, droplet size distribution in emulsions among several other applications Duynhoven et al., 2010;Marcone et al., 2012;Todt et al., 2001;Corrêa et al., 2009;Pereira et al., 2013;Santos et al., 2014). TD-NMR has also been used to study mass transport phenomenon in food products based on the attenuation of echo signal that is proportion to the analyte self-diffusion in the presence of static or pulsed magnetic field gradients Duynhoven et al., 2010). ...
... NMR spectroscopy has become an indispensable technique that can relate meso-and microstructural parameters to consumer-related features, such as shelf life and mouth feel [2]. Relatively low-cost and easy-to-handle benchtop NMR systems [3] have been developed, which operate at low magnetic fields, typically 0.47 T (20 MHz for 1 H) and this poses intrinsic limitations to sensitivity and resolution. Nevertheless, these systems have gained a considerable position in the food industry laboratories, where NMR is now routinely used for the assessment of water [4][5][6][7] and oil [8,9] droplet size distributions in food emulsions. ...
... In our implementation of the G-Var method, the calibration procedure is divided into three fully automated steps, as presented in Fig. 2. Application of a steady gradient during a PFG experiment is frequently used to narrow the echoes and obtain more reproducible fits [3]. Hence, we also implemented a steady gradient in the G-Var procedure (step 1 in Fig. 2). ...
The determination of water and oil droplet size distributions in food emulsions by low-field NMR has the advantage of a simple and non-perturbing sample preparation. Furthermore, NMR performs very well with respect to precision. The current implementation on most benchtop NMR spectrometers deploys a variation of gradient duration and requires continuous corrections for gradient imbalances, thus making the whole procedure a time-consuming one. By using variation of gradient strength and further stretching the capability of commercial benchtop NMR spectrometers, both water and oil droplet sizes can be measured in a more rapid manner, typically two to three times faster. The measured droplet size distributions are equivalent to those assessed by the current (slow) method, for both O/W and W/O emulsions. Furthermore, the rapid method shows a good performance with respect to precision. In addition, the method is able to determine droplet sizes in samples with much smaller amounts of dispersed phase.
... Recently, some rapid and non-destructive detection technologies , such as near infrared technique, X-ray, fluorescence , and acoustic technique, have been developed to replace them (Scotter 1997; Butz et al. 2005; Valous et al. 2009). Low field nuclear magnetic resonance (LF NMR) is also a powerful non-invasive method used in food quality control (Todt et al. 2001Todt et al. , 2006a Guthausen et al. 2006; Ghosh and Tombokan 2009). The first application of LF NMR was for solid fat content measurement on fat compositions at the year of 1970 (Todt et al. 2006b), which is well known as an international standard method (American Oil Chemists' Society 1993). ...
... The first application of LF NMR was for solid fat content measurement on fat compositions at the year of 1970 (Todt et al. 2006b), which is well known as an international standard method (American Oil Chemists' Society 1993). Due to the technical development of hardware and pulse sequences, more and more standard applications such as water, oil (or fat), and droplet size measurements have been developed (American Oil Chemists' Society 1995; Todt et al. 2001). The use of LF NMR on-line (or in situ) and the rapid measurements it generates guarantee real-time cereal food processing control (Ghosh and Tombokan 2009 ). ...
The classification analysis and firmness prediction of sweet corn subjected to different treatments were investigated to develop
the potential application of low field nuclear magnetic resonance for food quality control. Principal component analysis (PCA)
was firstly used for exploiting the invisible changes of the internal characteristics of blanched sweet corn. Then, two classification
methods involving regression analysis in combination with linear discriminant analysis (LDA), which is based on data compression
technology (PCA and partial least squares, PLS), were compared. The PCA score plots clearly showed that the samples varied
according to the temperature of the treatment. For the goal of classification, the principal components extracted from the
PLS analysis were more useful than those obtained from PCA. Cross validation was helpful to determine the appropriate number
of principal components. In fact, it proved that PLS combined with LDA yielded the highest success classification rate (94.3%),
and PLS also performed well in firmness prediction of processed sweet corn.
KeywordsFood processing-Quality control-Classification-Prediction-PLS-Low field NMR
... The lipid content, polyunsaturated fatty acids (PUFA), and iodine value can be determined using NMR and the sensitivity of NMR improves as the magnetic field strength increases (Challagulla et al. 2016). The methylene peak found during the NMR analysis, commonly indicate the presence of lipid (generally TAGs) (Todt et al. 2001). Further, the analytical technique of GC-MS is also widely used in the characterization of the fatty acid alkyl ester and its amount in biofuel. ...
The demand for fossil fuels has resulted in their rapid depletion and rise in the fuel costs. Moreover, fossil fuels have serious negative impacts on the environment due to their harmful emissions leading to global warming. This has paved the way for research into finding a renewable alternative to fossil fuels and exploring potential biofuel feedstocks. Biofuels are non-toxic, renewable, and have properties that are similar to conventional fuels. Among the studied feed-stocks, microalgae serve as a viable biofuel feedstock due to a number of advantages over another plant-based feed-stocks. Algal biofuels can help to restore the former green environment by completely replacing fossil fuels. However, only large-scale production and commercialization can meet these requirements. Numerous studies have been conducted to screen algal species with higher lipid yield. Despite decades of intensive research, biofuels have not reached the target of replacing conventional fuels. This is due to the challenges at every stage of its production process, starting from large-scale cultivation to commercial release of product. Novel lipid recovery strategies can be employed to tackle these limitations. For example, hybrid liquid biphasic system can be used to decrease the production costs (Yong et al. in J Water Process Eng 38: 101665, 2020). The aim of the review is to summarize the up to date research in the field of algae biofuels and to bring the focus on characterization and commercialization of algal lipids as a source of alternate energy. Furthermore, strategies to improve lipid accumulation and challenges associated with existing technologies are also discussed.
... Nuclear magnetic resonance (NMR) is a simple, rapid, and nondestructive method for characterizing the quality of food (Santos, Pereira-Filho, and Colnago 2016;Todt et al. 2001;Todt et al. 2008). The general theory of NMR is based on the excitation of energy absorbed by a nucleus which is placed in a uniform magnetic field where radio frequency pulses at proper frequency are terminated simultaneously (Slichter 2013). ...
Adulteration of edible substances is a potent contemporary food safety issue. Perhaps the overt concern derives from the fact that adulterants pose serious ill effects on human health. Edible oils are one of the most adulterated food products. Perpetrators are adopting ways and means that effectively masks the presence of the adulterants from human organoleptic limits and traditional oil adulteration detection techniques. This review embodies a detailed account of chemical, biosensors, chromatography, spectroscopy, differential scanning calorimetry, non-thermal plasma, dielectric spectroscopy research carried out in the area of falsification assessment of edible oils for the past three decades and a collection of patented oil adulteration detection techniques. The detection techniques reviewed have some advantages and certain limitations, chemical tests are simple; biosensors and nuclear magnetic resonance are rapid but have a low sensitivity; chromatography and spectroscopy are highly accurate with a deterring price tag; dielectric spectroscopy is rapid can be portable and has on-line compatibility; however, the results are susceptible to variation of electric current frequency and intrinsic factors (moisture, temperature, structural composition). This review paper can be useful for scientists or for knowledge seekers eager to be abreast with edible oil adulteration detection techniques.
... The first applications of commercial TD-NMR instruments were in food quality control and the determination of oil content in intact oilseeds [2]. Modern day applications of TD-NMR started around the year 2000 when versatile pulse programs and more user friendly computational interfaces were introduced [1]. ...
In this contribution, a selective overview of low field, time-domain NMR (TD-NMR) applications in the agriculture and agrifood sectors is presented. The first applications of commercial TD-NMR instruments were in food and agriculture domains. Many of these earlier methods have now been recognized as standard methods by several international agencies. Since 2000, several new applications have been developed, using state of the art instruments, new pulse sequences and new signal processing methods. TD-NMR is expected, in the coming years, to become even more important in quality control of fresh food and agricultural products, as well as for a wide range of food-processed products. TD-NMR systems provide excellent means to collect data relevant for use in the agricultural environment and the bioenergy industry. Data and information collected by TD-NMR systems thus may support decision makers in business and public organizations.
... In contrast, NMR measures the displacement of the self-diffusing oil molecules in each individual droplet, which is restricted by the droplet wall. Hence, the average size of individual droplets present in a cluster is calculated [33][34][35][36][37][38][39]. Exemplary light microscopic images confirm the presence of oil droplet clusters, in particular, for emulsions with low protein to oil ratios (Fig. 3). ...
Microencapsulation of oxidation sensitive oils aims to separate lipids from the environmental oxygen by embedding oil droplets in a solid matrix, which builds a physical barrier. Some oil droplets are not fully incorporated and are in contact with the powder surface generating surface oil. It is proposed that the probability of oil droplets being in contact with the particle surface increases with the oil droplet size. The aim of the study is to investigate the impact of the oil droplet size on the encapsulation efficiency (EE). Two sets of feed emulsions differing in the applied homogenization pressure and in the protein to oil ratio were spray dried using a pilot plant spray dryer. The oil droplet size of the emulsion was determined by static light scattering (SLS). In addition, nuclear magnetic resonance (NMR) was used to measure the d3,2 of oil droplets in the emulsion and in the powder before and after surface oil removal. Encapsulates were analyzed regarding aw, moisture content, particle size, oil load and EE. The oil droplet size in the emulsion decreased with increasing protein to oil ratio as well as with the homogenization pressure. Large oil droplets and in particular droplet clusters resulted in more non-encapsulated oil. The experimentally determined EE was in accordance with the theoretical one, calculated based on the droplet and particle diameter. For emulsions with a diameter > 1 µm, the d3,2 decreased in the powder and further by removing the surface oil, which was related to the deformation of oil droplets contributing to the non-encapsulated oil.
... These devices in contrast to high field NMR are much cheaper and robust regarding environmental influences. Especially in food industry TD-NMR has become an important tool for quality control (QC) e.g. to analyze moisture and water content in the presence of lipids [12][13][14] or to determine the solid fat content in fat mixtures to name two prominent examples [15][16][17]. ...
Time domain, also named lowfield nuclear magnetic resonance is used to monitor oil degradation by measuring relaxation and diffusion. As quality control of oils is indispensable to optimize oil change intervals while simultaneously preventing machinery damage, the technique was applied to detect the degradation state of engine oils as time domain nuclear magnetic resonance is known as a well suited tool to measure quality control parameters for example in food industry. Correlations with commonly applied oil analytics like viscosity measurements and inductively coupled plasma optical emission spectrometry allow to interpret relaxation and diffusion data in detail and finally to deepen the understanding of oil aging processes. Additionally, the measurement temperature was varied to achieve the maximum sensitivity towards oil aging. Low field NMR is not only realized in form of table top instruments, but also in form of field cycling and single sided NMR devices. Fast field cycling as well as single-sided NMR were also explored to study oil aging and to provide valuable insight. The latter device was used to obtain information about translational diffusion and transverse relaxation of oils simultaneously.
... Additionally, the diameter measured by static light scattering (SLS) and nuclear magnetic resonance (NMR) differed at concentrations below 0.07 g (w/w) protein per oil. Due to different measurement principles, the latter method measures the size of individual droplets, whereas SLS determines the average diameter of droplet clusters [6], [7]. Insufficient concentrations of soy protein lead to droplet flocculation, which was confirmed by light microscopy (data not shown). ...
Potential factors leading to surface oil were investigated by analyzing the impact of emulsion properties, atomization and drying conditions separately. An increased oil load, droplet size and in particular the size of droplet aggregates led to significant more surface oil. Increasing the viscosity, inlet temperature and relative humidity resulted in larger particles with a higher encapsulation efficiency. The results indicate that the probability of oil droplets being in contact with the particle surface determines the amount of surface oil. Oil diffusion towards the surface was excluded due to the short residence times and high viscosities. Keywords: microencapsulation; encapsulation efficiency; emulsion properties; atomization; drying conditions
... In comparison to ordinary NMR, TD-NMR is faster, easier to use, and less expensive [218]. Todt et al. [219] reported that TD-NMR is based on the different relaxation times of hydrogen nuclei in different phases of the sample being analyzed. ...
... The development of tabletop NMR relaxometers had started by addressing the needs of the food industry for a reliable method to determine the solid fat content [7,49]. Today this is still the major application of tabletop NMR followed by droplet sizing of emulsions and liquid typing and quantification in products such as oil in olives [49][50][51][52][53][54][55][56]. The droplet sizing technique has recently been extended to the characterization of double emulsions, where molecular exchange between different compartments of the same phase poses new challenges [57]. ...
NMR with mobile and compact devices is experiencing considerable growth in recent years in particular since instruments have become available, which are capable not only of measuring NMR relaxation but also images and high-resolution spectra. Based on permanent magnet technology, compact tabletop NMR instruments measure samples of materials and solutions positioned inside the magnet, while compact mobile instruments measure material properties of intact objects and samples nondestructively in the inhomogeneous stray field outside the magnet. Following a brief introduction to NMR with homogeneous and inhomogeneous magnetic fields and to the concepts of permanent center- and stray-field NMR magnets, the evolution of the technology over the past 10 years is reviewed and illustrated with selected applications. Relaxation and diffusion measurements find use in the analysis of foods, biological tissues, polymer materials, porous media, and objects of cultural heritage. Compact imaging instruments are mainly employed to study crops and plants as well as transport phenomena in chemical engineering and geophysics. Tabletop NMR spectrometers find increasing use in educational institutions and for chemical analysis and reaction monitoring on the workbench and in the fume hood of the synthesis laboratory, and they are being explored as a tool for process control.
... [47] Nuclear magnetic resonance spectroscopy Nuclear magnetic resonance (NMR), first proposed by Rabi et al., [48] is based on the property of certain nuclei to absorb and emit energy under a magnetic field. NMR has become one of the most powerful lipid analysis techniques, with application to both liquid and solid samples (including aggregates of cells; [49] NMR active nuclei in lipid molecules include ( 1 H), carbon ( 13 C), phosphorus ( 31 P), oxygen ( 17 O)), of which only H is in high abundance in algal cells [50] and thus it is most commonly considered. [51] There are several NMR methods each with limitations and advantages. ...
Microalgae are a varied group of organisms with considerable commercial potential as sources of various biochemicals, storage molecules and metabolites such as lipids, sugars, amino acids, pigments and toxins. Algal lipids can be processed to bio-oils and biodiesel. The conventional method to estimate algal lipids is based on extraction using solvents and quantification by gravimetry or chromatography. Such methods are time consuming, use hazardous chemicals and are labor intensive. For rapid screening of prospective algae or for management decisions (e.g. decision on timing of harvest), a rapid, high throughput, reliable, accurate, cost effective and preferably nondestructive analytical technique is desirable. This manuscript reviews the application of fluorescent lipid soluble dyes (Nile Red and BODIPY 505/515), nuclear magnetic resonance (NMR), Raman, Fourier transform infrared (FTIR) and near infrared (NIR) spectroscopy for the assessment of lipids in microalgae. Download PDF at http://www.tandfonline.com/eprint/7umAAgYWANTZT7hUgKPp/full
... Emitted radiowaves have variable frequencies and each frequency serves as a fingerprint for a particular chemical species present in a given chemical environment. Typical components of an NMR instrument are shown in Figure 2. (Todt 2001). TD-NMR is cheaper as it works under low magnetic field (using a permanent magnet). ...
Microalgal oil has been a source for production of biofuels such as bio-oil and biodiesel. These two biofuels can be characterized quantitatively using advanced instrumentation techniques. Nile Red fluorescence method, PAM fluorometry, NMR, GC/GC-MS and FTIR are among the major techniques available for characterization and quantification of algal oil. NMR is a rapid and non-destructive analytical technique as it requires minimal sample preparation and even one intact algal cell can be analyzed. It can also be used for continuous monitoring of cellular composition of algal culture. NMR can be used to monitor transesterification reactions and oxidation of lipids and biodiesel components. GC has remained the most widely used analytical technique for fatty acid profile analysis. GC-MS is a destructive analytical technique as derivatization of algal oil is required owing to its poor volatility and hence involves lengthy sample preparation procedure. FTIR is a relatively inexpensive technique, and like NMR, can analyze intact cells with scanning time in the order of seconds. FTIR may offer high signal-to-noise ratio and can also be used to monitor transesterification.
... The principle of NMR is based on the relaxation time of the hydrogen molecule in a compound of interest (Todt et al. 2001). Time-Domain Nuclear Magnetic Resonance (TD-NMR), also known as low resolution NMR, was introduced 35 years ago through the efforts of Unilever Research in the Netherlands (Todt et al. 2006). ...
... For samples with different chemical properties, such as hydrogen content and chemical structure of hydrogen-containing compound, the relaxation times are different. As a rapid, convenient, and nondestructive method, LF- NMR has been abundantly used in food material property measurements and quality control (Todt et al. 2001; Micklander et al. 2002; Todt et al. 2006a) based upon detection of the mobility and distribution of water and fat hydrogen protons (Blümich et al. 2009) which extensively exist in food matrix. Different kinds of protons, e.g., those bound in free water or in more structured water or even protons attached to lipids, proteins, and carbohydrates, can be distinguished by LF-NMR (Pedersen et al. 2000). ...
Pleasant flavor and nutritional benefits of vegetable oils lead to an increase in their consumption amount. In addition, due to being apparently similar to commercially qualified vegetable oils (QVOs), used frying oil (UFO) is added into it to seek high profit by the unscrupulous traders. Thus, the authenticity assurance of commercial oil and fat products remains a challenge to scientists both in terms of its health and commercial perspectives. This work focused on using low field nuclear magnetic resonance (LF-NMR) to discriminate the adulteration of commercial corn, peanut, rapeseed, and soybean oils with two kinds of UFOs. The differences between the transverse relaxation distributions (T
2 distributions) of qualified oil and UFO were in the appearance of the third peak (A), which could be assigned to polymer products that were produced during the deep-fat frying process and the shift of T
2 value of the peaks. In addition, the A peak area accounted for the whole area of peaks linearly increasing along with the increase in adulteration proportion. Based on the changes of peak area, a simple linear equation was built and the determination coefficients (R
2) were all higher than 0.93. Therefore, as a rapid, convenient, and nondestructive method, LF-NMR application could be used to detect adulteration of vegetable oils with UFO.
... Localization of specific voxels by TD-NMR is hampered by the low resolution of this technique. However, TD-NMR provided detailed information on mobility behaviour of molecules such as water, starch and lipid compounds in seeds, olives, nuts, chocolate, milk powder and cheese (Todt et al., 2001). The upper limit of water content for lipid determination by TD-NMR without pre-drying of the sample is about 15% (ISO, 1993) water content, far lower than that measured in the developing wheat kernels analysed here. ...
Spikes and seeds from diploid ‘einkorn’ wheat Triticum monococcum and two near-isogenic hard and soft common wheat (Triticum aestivum) lines were harvested at regular intervals from 7 days post-anthesis (dpa) and analysed by non-destructive magnetic resonance imaging (MRI) and time domain-nuclear magnetic resonance (TD-NMR). A large amount of free water occurred in rachises, glumes and awns of spikes collected at 7 dpa, and accumulated in the physiologically active cells of the endosperm at 21 dpa. In the final stages of kernel development, awns and seed embryos exhibited a high MR signal due to the presence of free water likely associated with biological activities. TD-NMR relaxation time distributions obtained by discrete exponential fitting, distributed exponential fitting and SLICING multivariate analysis offered detailed information on mobility behaviour of water molecules in developing seeds and were able to differentiate two soft and hard isolines from common wheat cv. Enesco at early stages of seed development.
... The spin–echo NMR pulse sequence experiment used for lipid and moisture determination. petroleum, pharmaceutical, agricultural, and food industries (Todt et al., 2001). TD-NMR capitalizes on the differing relaxation times of hydrogen nuclei contained in the solid or liquid phases of the material being examined (Ruan and Chen, 1998), and spin–spin transverse relaxation times, T 2 , can be readily measured using CPMG pulse sequences (Meiboom and Gill, 1958). ...
Starch-lipid composites, prepared by excess steam jet cooking aqueous mixtures of starch and lipid, are used in a broad range of applications for which their performance can depend upon accurately knowing the amount of the lipid contributed by the composites. A rapid and non-destructive method based on time-domain nuclear magnetic resonance spectroscopy (TD-NMR) was evaluated to quantitate soybean oil (SBO) or butterfat (BF) content in a series of dried starch-lipid composites. Transverse hydrogen relaxation (T2) properties of the composites were examined using Carr, Purcell, Mieboom, Gill (CPMG) pulse experiments and multi-exponential decay fitting routines were utilized to evaluate the various components. Spin-echo TD-NMR experiments were used to quantitate the amount of lipid in the composites and agreed well with lipid extraction experiments (R2 = 0.998). Moisture levels in the composites were also simultaneously determined and compared reasonably well to moisture levels determined gravimetrically (R2 = 0.881). TD-NMR was shown to be a rapid method to determine lipid and moisture content in these starch-lipid composites without the need for labor intensive extraction and gravimetric methods currently employed.
In this review, we focus on the recent developments in time domain Nuclear Magnetic Resonance (TD-NMR). The Introduction section describes the methods usually adopted for assessment food quality, whereas the second paragraph illustrates the basic physical principles of the TD-NMR technique. In the third section we discuss the principal application of the TD-NMR method in food science. In fact, in the last decades the TD-NMR has become one of the most efficient and advanced techniques for analysis of food products. In TD-NMR technique, the proton relaxation (transversal relaxation, T2) is monitored providing information about the mobility of the nuclei. TD-NMR is principally used for monitoring the fat composition of food products, which represents a crucial parameter to be considered for controlling the food properties and improving its quality. This paper will present a summary of the most important applications of low field TD-NMR technique in food science, and the results of the most important researches.
The impact of spray drying conditions on encapsulated rapeseed oil was investigated regarding the encapsulation efficiency (EE). The drying rate was modified by the solid content (25–55% w/w) of atomized feed droplets, the inlet temperature (140–220 °C) and relative humidity (0.12–1.57%) of the drying air. The moisture, aw, bulk and tapped density, particle size, and EE were analyzed. An accelerated drying rate due to a higher solid content and inlet temperature as well as a slower drying induced by an increased air humidity resulted in larger particle and more efficient encapsulation. A higher EE was obtained with increasing particle size which is in accordance with a theoretical EE calculated based on the particle- and oil droplet diameter.
Oil is a prominent, but multifaceted material class with a wide variety of applications. Technical oils, crude oils as well as edibles are main subclasses. In this review, the question is addressed how low field NMR can contribute in oil characterization as an analytical tool, mainly with respect to quality control. Prerequisite in the development of a quality control application, however, is a detailed understanding of the oils and of the measurement. Low field NMR is known as a rich methodical toolbox which was and is explored and further developed to address questions about oils, their quality and usability as raw materials, during production and formulation as well as in use.
In this chapter, an overview is given about the main time domain (TD) proton nuclear magnetic resonance (1H NMR) transversal relaxation studies on cereal products. Because of the scope of this book, first an introduction is given on changes of the main biopolymers during baking and storage of wheat bread, one of the most studied cereal products. TD ¹H NMR is an excellent technique to study the molecular mobility of water and biopolymers during processing and storage of cereal products including bread. Due to their complexity, starch-based model systems are often used to understand and interpret the complex NMR transversal relaxation time distributions of these products. Comparison of NMR relaxation data of the model systems and those of cereal products reveals that changes in proton mobility during processing and storage are largely caused by changes in the starch fraction, which is the main constituent of flour, and concomitant redistribution of water. Furthermore, a relationship exists between proton mobility on a molecular scale and the macroscopic textural properties of the food product, making TD ¹H NMR transversal relaxometry a very suitable technique to predict product quality. © Springer International Publishing AG, part of Springer Nature 2018.
Encapsulation is an established technique to protect sensitive materials from environmental stress. In order to understand the physical protection mechanism against oxidation, knowledge about the powder microstructure is required. TD-NMR has the potential to determine the surface oil and droplet size distribution by relaxation and restricted self-diffusion, respectively.
The amount of surface oil, the retention and encapsulation efficiency are determined based on a lipid balance. The oil load of the initial powder and after surface oil removal is measured by TD-NMR. The results correlate with gravimetric and photometric references.
The oil droplet size obtained by TD-NMR correlates well with static light scattering (SLS). The diameter of droplets in emulsions and dried powder both measured by TD-NMR, correlates (r = 0.998), implying that oil droplets encapsulated by a solid matrix can be measured.
Summarizing, TD-NMR allows analysis of the microstructure of encapsulated lipid powders, in a rapid, simple and non-destructive way.
In this chapter, an overview is given about the main time domain (TD) proton nuclear magnetic resonance (1H NMR) transversal relaxation studies on cereal products. Because of the scope of this book, first an introduction is given on changes of the main biopolymers during baking and storage of wheat bread, one of the most studied cereal products. TD 1H NMR is an excellent technique to study the molecular mobility of water and biopolymers during processing and storage of cereal products including bread. Due to their complexity, starch-based model systems are often used to understand and interpret the complex NMR transversal relaxation time distributions of these products. Comparison of NMR relaxation data of the model systems and those of cereal products reveals that changes in proton mobility during processing and storage are largely caused by changes in the starch fraction, which is the main constituent of flour, and concomitant redistribution of water. Furthermore, a relationship exists between proton mobility on a molecular scale and the macroscopic textural properties of the food product, making TD 1H NMR transversal relaxometry a very suitable technique to predict product quality.
H low-field nuclear magnetic resonance (LF-NMR) and chemometrics were employed to screen the quality changes of peanut oil (PEO) adulterated with soybean oil (SO), rapeseed oil (RO), or palm oil (PAO) in ratios ranging from 0% to 100%. Significant differences in the LF-NMR parameters, single component relaxation time (T2W), and peak area proportion (S21 and S22), were detected between pure and adulterated peanut oil samples. As the ratio of adulteration increased, the T2W, S21, and S22 changed linearly; however, the multicomponent relaxation times (T21 and T22) changed slightly. The established principal component analysis or discriminant analysis models can correctly differentiate authentic PEO from fake and adulterated samples with at least 10% of SO, RO, or PAO. The binary blends of oils can be clearly classified by discriminant analysis when the adulteration ratio is above 30%, illustrating possible applications in screening the oil species in peanut oil blends.
The ratio between liquid and solid portion of lipid can be determined quickly and accurately by low-field pulsed nuclear magnetic resonance (LFP-NMR) instrument. This analytical tool has become one of important techniques to characterize product physical properties especially related to fat melting behavior, mouth feeling, and cooling effect etc. in lipid and food application system. In lipid, it can be used to determine the solid fat content, evaluate the crystallization rate and the compatibility of lipid blends, monitor the enzymatic interesterification degree, and estimate the fat crystal type. As a nondestructive testing, LFP-NMR technique was also applied to analyze the particle size distribution of emulsion, the fat crystallization, and the quality control during food storage. LFP-NMR is not only applied to evaluate the fat crystallization, but also to analyze the crystallinity of sugar. These application progresses of LFP-NMR technique in lipid and food will be summarized in this chapter. © 2015 Bentham Science Publishers Ltd. Published by Elsevier Inc. All rights reserved.
The rapid and real-time lipid determination can provide valuable information on process regulation and optimization in the algal lipid mass production. In this study, a rapid, accurate and precise quantification method of in vivo cellular lipids of Chlorella protothecoides using low field nuclear magnetic resonance (LF-NMR) was newly developed. LF-NMR was extremely sensitive to the algal lipids with the limits of the detection (LOD) of 0.0026g and 0.32g/L in dry lipid samples and algal broth, respectively, as well as limits of quantification (LOQ) of 0.0093g and 1.18g/L. Moreover, the LF-NMR signal was specifically proportional to the cellular lipids of C. protothecoides, thus the superior regression curves existing in a wide detection range from 0.02 to 0.42g for dry lipids and from 1.12 to 8.97gL(-1) of lipid concentration for in vivo lipid quantification were obtained with all R(2) higher than 0.99, irrespective of the lipid content and fatty acids profile variations. The accuracy of this novel method was further verified to be reliable by comparing lipid quantification results to those obtained by GC-MS. And the relative standard deviation (RSD) of LF-NMR results were smaller than 2%, suggesting the precision of this method. Finally, this method was successfully used in the on-line lipid monitoring during the algal lipid fermentation processes, making it possible for better understanding of the lipid accumulation mechanism and dynamic bioprocess control.
Microalgal oil has been a source for production of biofuels such as bio-oil and biodiesel. These two biofuels can be characterized quantitatively using advanced instrumentation techniques. Nile red fluorescence method, PAM fluorometry, NMR, GC/GC-MS, and FTIR are among the major techniques available for characterization and quantification of algal oil. NMR is a rapid and nondestructive analytical technique as it requires minimal sample preparation, and even one intact algal cell can be analyzed. It can also be used for continuous monitoring of cellular composition of algal culture. NMR can be used to monitor transesterification reaction and oxidation of lipids and biodiesel components. GC has remained the most widely used analytical technique for fatty acid profile analysis. GC-MS is a destructive analytical technique as derivatization of algal oil is required owing to its poor volatility and hence involves lengthy sample preparation procedure. FTIR is a relatively inexpensive technique and, like NMR, can analyze intact cells with scanning time of the order of seconds. FTIR may offer high signal-to-noise ratio and can also be used to monitor transesterification.
There is an increasing concern that global oil production has nearly reached its peak and this peak will be followed by a rapid decline in the oil production. This concern accentuates the significance of understanding in more depth the challenges in each unit operation involved in the production of oil in the petrochemical industry. A discussion on petrochemical product and process control using rapid TD-NMR technology covers the development of technology towards a more economical, effective, and environmentally safe process; the basic principle of TD-NMR; challenges involved in the downstream process of oil production; separation of complex mixtures by distillation into fractions, e.g., gasoline; environmental concerns; measurement of bitumen and water content in oil sands; and automating the measurement procedure. This is an abstract of a paper presented at the 2009 AIChE Spring National Meeting and 5th Global Congress on Process Safety (Tampa, FL 4/26-30/2009).
Hyphenated low-field NMR techniques are promising characterization methods for online process analytics and comprehensive offline studies of soft materials. By combining different analytical methods with low-field NMR, information on chemical and physical properties can be correlated with molecular dynamics and complementary chemical information. In this review, we present three hyphenated low-field NMR techniques: a combination of near-infrared spectroscopy and time-domain NMR (TD-NMR) relaxometry, online (1) H-NMR spectroscopy measured directly after size exclusion chromatographic (SEC, also known as GPC) separation and a combination of rheometry and TD-NMR relaxometry for highly viscous materials. Case studies are reviewed that underline the possibilities and challenges of the different hyphenated low-field NMR methods. Copyright © 2015 John Wiley & Sons, Ltd.
Copyright © 2015 John Wiley & Sons, Ltd.
Nuclear Magnetic Resonance (NMR) spectroscopy is well recognized procedure to check the identity and structure of chemical compounds. It also provides new approaches for the edible oils and fats analysis. It is well on its path for the utilization as a green and non-destructive analytical technique to check the quality of edible oils in edible oil processing industries. This chapter provides brief information of the application of NMR spectroscopy for the determination of important parameters of edible oils. It is anticipated that number of classical standard methods which are based on titration will be substituted by this technique in near future. Because, use of costly organic solvents could be avoided using external deuterium lock or very small quantity of deuterated solvents are used which will not only cut the cost of solvents and chemicals but also favors to environment from their potential risk of toxicity. From the perspective of quality control (QC) practice, the classical methods are laborious, time consuming and without documentary proof. While NMR spectroscopic results are very clear, accurate and reproducible containing a documentary proof in the form of NMR spectra.
Since its discovery in 1945 [1, 2], nuclear magnetic resonance (NMR) has developed into an inexhaustible research field. It is exploited in several areas in physics, chemistry, biology, and medicine to extract unique information at the molecular level [3–8]. In chemistry, for example, it is considered to be one of the most powerful analytical tools to elucidate molecular structure, and in medicine it is routinely used for diagnostic imaging. Driven by the fact that sensitivity and spectral resolution increase with the magnetic field strength and homogeneity, magnets are built larger and larger over the years. Today, magnets are heavy and static devices installed in special NMR laboratories designed to shield electromagnetic interference and reduce magnetic field distortions in order to provide ideal experimental conditions (Fig. 1.1a). Besides the fact that samples of interest must be taken to the magnet, they must fit into the limited space available in the bore of the magnet. These issues are certainly a limitation when arbitrarily large samples require non-destructive analysis.
For the detection of defects, evaluation of internal quality and analysis of internal structures in food and biological materials, there is a number of image acquisition techniques available so far. Among them, MRI has the advantage of allowing a variety of measurements to be made that not only contribute to the evaluation of maturity and quality parameters in fruits and vegetables and other food materials but also improve the understanding of underlying physiological processes. So, the ability of MRI to function in a completely non-destructive and to encode molecular dynamics through different contrast mechanism has encouraged developments of many applications in various fields. An overview of MRI as non-destructive detection in quality of food and agricultural produce and its application in postharvest sorting and processing have been presented in this paper. This paper elaborated principle of MRI, function of its components, quality detection methods, and discussed recent research and applications. Since, no paper yet published on MRI, covered so wide applications as included in this work, its importance being increased more.
The development of NMR instrumentation, methods, and applications of mobile NMR, with particular attention to single-sided NMR is discussed. Inside-out NMR is a form of single-sided or unilateral NMR, where an NMR sensor much smaller than the object is placed near the object to acquire signals from the object volume near the sensor. Mobile NMR holds great promise in a variety of fields, in particular in medicine, materials science, chemical engineering and space science. A very promising area of application of mobile NMR is process control by sensors installed in the production line. The development of NMR methods for mobile NMR is driven by two sources. One is the need for more information from, and better accuracy of, well-logging instruments. The other is scientific curiosity about doing NMR in low and inhomogeneous fields with inexpensive instrumentation and with it the drive for expanding the range of applications of NMR.
Nuclear Magnetic Resonance (NMR) Spectroscopy has been extensively used for the analysis of olive
oil and it has been established as a valuable tool for its quality assessment and authenticity. To date,
a large number of research and review articles have been published with regards to the analysis of
olive oil reflecting the potential of the NMR technique in these studies. In this critical review, we cover
recent results in the field and discuss deficiencies and precautions of the three NMR techniques (1H, 13C,
31P) used for the analysis of olive oil. The two methodological approaches of metabonomics, metabolic
profiling and metabolic fingerprinting, and the statistical methods applied for the classification of olive
oils will be discussed in critical way. Some useful information about sample preparation, the required
instrumentation for an effective analysis, the experimental conditions and data processing for obtaining
high quality spectra will be presented as well. Finally, a constructive criticism will be exercised on the
present methodologies used for the quality control and authentication of olive oil.
Low-field NMR instrumentation offers a user-friendly and cost-effective means for assessment of water and oil droplet size measurements in food emulsions. Examples are given of major food application areas, and these are supported with validation data in terms of precision and equivalence to other methods. The NMR method gives the same results as other techniques, such as microscopy, laser diffraction and electric sensing, but with similar or better precision. NMR distinguishes itself by a simple and non-perturbing sample preparation procedure (in addition to the aforementioned advantages). For reliable results, the NMR parameters should be properly chosen and adjusted. A survey is given of experimental NMR parameters than can have an impact on the performance of water and oil droplet size determination. Copyright © 2002 John Wiley & Sons, Ltd.
Recently, NMR has been demonstrated in a truly non-invasive through-package ‘sensor’ mode, also denoted as the MObile Universal Surface Explorer (MOUSE). In this feasibility study, we present a first example where we use the MOUSE sensor for assessment of the microstructural quality of a food material. We have taken model systems consisting of protein-stabilized oil-in-water emulsions, where an important microstructural quality parameter is water exudation (WE). In order to establish a sound relation between MOUSE signals and WE, it was necessary to deploy multivariate calibration techniques. It was found that the performance of the MOUSE is comparable to that of conventional benchtop NMR. Thus it was demonstrated that the NMR MOUSE presents a good option for non-invasive assessment of microstructural quality parameters, e.g. in manufacturing and in the supply chain.
Time-domain nuclear magnetic resonance (TD-NMR) is widely used within food industries for QC/QA applications. Precise determination of moisture and water is of fundamental interest. To determine moisture and water in the presence of lipids, the minispec makes use of differences in their respective NMR relaxation properties. The minispec applications analysing bound water are well-known and have become International standard methods. Different methods to analyse food samples with high water content or free water, like some dairy products, are addressed in this paper. Explicitly, the well-known pre-drying methods are compared to NMR diffusion experiments and a combined relaxation time analysis. Finally the single-sided NMR approach is discussed to analyse packages food.
NMR has become a valuable tool in the study of a wide variety of structural and compositional aspects of food chemistry and food analysis. P NMR spectroscopy has been an invaluable tool in the analysis of foods and the study of the factors affecting food quality. P NMR spectra of intact muscle with or without deuterium locking have been used with great success, obtained either by utilizing large bore magnets or horizontal MRI scanners. Foodstuff such as in milk, where phosphorus appears in the form of phospholipids, elaborate experimental procedures have been developed in order to acquire high resolution P NMR spectra. P NMR has been used to measure the phospholipid content of Greek extra-virgin olive oil, identifying PA, PI, and the hydrolyzed lyso analogues, LPA and LPI as the most abundant PLs. The P-tagging NMR methodology has also been applied to study the effect of thermal stressing on saturated and unsaturated seed oils.
Understanding the relations between sensory/physical parameters and the underlying microstructural features is an essential step for designing and manufacturing novel food products. ‘Deductive’ strategies to derive such structure–property relationships operate on time-scales, which do not match with the currently required pace of research and development. In this work an ‘inductive’ approach has been outlined that deploys benchtop spectroscopic NMR and NIR measurements and multi-variate data analysis in order to generate explorative models that relate microstructure and functional parameters. Using protein-stabilised oil-in-water model emulsions, the use of a partial least squares and a multi-linear regression approach for processing and analysis of time-domain NMR data is demonstrated, and benchmarked against the deployment of NIR spectroscopy.
Due to its non-invasive nature and its ability to be implemented on downsized benchtop equipment, PFG NMR is gaining popularity as a droplet sizing tool in food emulsions. Food scientists and technologists should be aware of assumptions that are made with respect to PFG NMR methodology and mathematical models used for calculating droplet size distributions. This also needs to be considered when comparing results of NMR with other techniques. Several novel measurement and data modeling approaches have emerged that bring improvements in speed, sensitivity, accuracy and ability to probe dynamic events in real-time and in-situ.
Time-domain NMR is being used throughout all areas of food science and technology. A wide range of one- and two-dimensional relaxometric and diffusometric applications have been implemented on cost-effective, robust and easy-to-use benchtop NMR equipment. Time-domain NMR applications do not only cover research and development but also quality and process control in the food supply chain. Here the opportunity to further downsize and tailor equipment has allowed for “mobile” sensor applications as well as online quality inspection. The structural and compositional information produced by time-domain NMR experiments requires adequate data-analysis techniques. Here one can distinguish model-driven approaches for hypothesis testing, as well as explorative multi-variate approaches for hypothesis generation. Developments in hardware and software will further enhance measurement speed and reveal more detailed structural features in complex food systems.
A study was conducted to demonstrate process and reaction monitoring by low-field nuclear magnetic resonance (NMR) spectroscopy. The study focused on the development of a robust low-field spectroscopic technique which had the potential to be widely applicable in an industrial or technical environment. The development was related to time-domain (TD-) NMR and high-field Fourier-transform (FT) NMR. Reaction monitoring by NMR had been performed inside the probe and the magnet, providing an in situ possibility for monitoring the reaction progress by diverse NMR methods. MAS-studies were also performed to observe polymerization, while heterogeneous catalytic reactions had been investigated by imaging methods. One of the most attractive features of quantitative NMR spectroscopy was that the proportionality of the peak area to the number of nuclei was essentially identical for all nuclei of the same species in a mixture.
The application of solid-state nuclear magnetic resonance (NMR) spectroscopy in analytical chemistry is described. The main application for this method is found in pharmacy where polymorphism plays an important role in the function of substances. Another important application of solid-state NMR is food science where information about the solid structures are essential for the understanding of the product properties. An important analytical application of solid-state NMR is in the field of inorganic materials as the nuclei commonly observed by NMR have half-integer spins larger than 1/2, which results in a nuclear quadrupolar moment.
This book is about pulse nuclear magnetic resonance (NMR), with its techniques, the information to be obtained, and practical advice on performing experiments. The emphasis is on the motivation and physical ideas underlying NMR experiments and the actual techniques, including the hardware used. The level is generally suitable for those to whom pulse NMR is a new technique, be they students in chemistry or physics on the one hand and research workers in biology, geology, or agriculture, on the other. The book can be used for a senior or first year graduate course where it could supplement the standard NMR texts.
Intense radiofrequency power in the form of pulses is applied to an ensemble of spins in a liquid placed in a large static magnetic field H0. The frequency of the pulsed r-f power satisfies the condition for nuclear magnetic resonance, and the pulses last for times which are short compared with the time in which the nutating macroscopic magnetic moment of the entire spin ensemble can decay. After removal of the pulses a non-equilibrium configuration of isochromatic macroscopic moments remains in which the moment vectors precess freely. Each moment vector has a magnitude at a given precession frequency which is determined by the distribution of Larmor frequencies imposed upon the ensemble by inhomogeneities in H0. At times determined by pulse sequences applied in the past the constructive interference of these moment vectors gives rise to observable spontaneous nuclear induction signals. The properties and underlying principles of these spin echo signals are discussed with use of the Bloch theory. Relaxation times are measured directly and accurately from the measurement of echo amplitudes. An analysis includes the effect on relaxation measurements of the self-diffusion of liquid molecules which contain resonant nuclei. Preliminary studies are made of several effects associated with spin echoes, including the observed shifts in magnetic resonance frequency of spins due to magnetic shielding of nuclei contained in molecules.
Publisher Summary
This chapter describes the techniques used for the determination of droplet size distributions, namely, pulsed field gradient nuclear magnetic resonance spectroscopy (PFG-NMR). Emulsions are the colloidal dispersions of liquid droplets in another liquid phase, sometimes stabilized by surface active agents. There are several reasons why it is important for a food company to examine emulsions carefully. In systems containing both oil and water, the knowledge of the emulsion structure may be important with respect to palatability, oral melting behavior, texture, and general appearance. Thus, emulsions consist of a discontinuous phase, dispersed in a continuous phase. The PFG-NMR technique can be readily used for the determination of the water droplet size distribution in W/O emulsions or the oil droplet size distributions in O/W emulsions. Its important advantages are the noninvasive nature, the ease of sample preparation, and the fact that PFG-NMR measures the droplet size distribution of the bulk in contrast with microscopic methods, which estimate the size distribution of the surface. Both the proposed matrix method and the iterative curve fitting procedure can be successfully applied in a factory environment. The method can be implemented on a high- as well as on a low-resolution NMR spectrometer. The low-resolution NMR method can be adapted for the routine determinations of water droplet size distributions of spreads, such as margarines and halvarine. Because of the modest price and relative simplicity of the low-resolution NMR equipment, this method can be used in a factory environment.
A new method for measuring oil droplet size distributions by means of a benchtop pulsed field gradient NMR spectrometer operating in the time domain is presented. The continuous water phase is successfully suppressed by gradient pulses in order to measure the dispersed oil phase. Simulations show that for most common oil/water food emulsions the influence of droplet diffusion is negligible due to a rather large droplet size or a high viscosity of the continuous water phase. The merits of the NMR method relative to other methods are discussed in terms of sample preparation, sensitivity to cluster phenomena, and matrix effects. Preliminary results of a short validation study show a good correlation with conventional reference techniques.
In 1972 Packer and Rees described a method for the determination of droplet size distributions in emulsions using the pulsed field gradient (PFG) NMR spin—echo technique. This paper describes an improved method, based on this earlier work, which is directed at the routine determination of water droplet size distributions of water-in-oil emulsions. The improvement is based on the recognition that a set of echo attenuation values (R) as a function of the field gradient pulse width, obtained under conditions where R is independent of the time allowed for diffusion, contains all the necessary information on the water droplet size distribution. The parameters of a log-normal distribution of water droplet sizes are easily obtained from a small number of measurements which are then compared with a matrix of sets of theoretical echo attenuations, representing different combinations of these parameters, using a simple computer program. The method is described and examples of results are shown. The effect of temperature on the measurements is discussed.
A method is described to obtain high resolution NMR images in solids. Line broadening effects are eliminated by observing the free induction decay signal at a fixed time while the experiment is repeated each time with incremented field gradient in equal steps for the spatial resolution. Solid images with excellent resolution are shown.
The pulsed‐gradient, spin‐echo technique has been used to study self‐diffusion of protons in several colloidal systems in order to examine the usefulness of that technique in determining the extent to which the free movement of molecules in these systems is restricted by the colloidal structures present. The pulsed‐gradient experiment is preferred to the steady‐gradient experiment because it affords better definition and control over the time during which diffusion is observed. Diffusion times between 1 sec and 10−3 sec have been used. One artificial system of thin liquid layers, three different kinds of plant cells, and one emulsion have been studied. Clear indications of restricted diffusion are found in all the systems. When fitted to theoretical expressions derived for such behavior, the data yielded a description of each system, as seen by the diffusing molecules, adequately in agreement with the known structure and properties. Critiera for recognizing and analyzing restricted diffusion are discussed. Necessary conditions for the successful study of restricted diffusion are also discussed.
The Bloch—Torrey equations are modified to include the case of anisotropic, restricted diffusion and flow. The problem of solving these modified equations for the amplitude of a spin echo in a time-dependent magnetic-field gradient subject to restricting boundary conditions is discussed. This problem is solved for a number of selected cases. In particular, it is found that a magnetic-field gradient applied in short, intense pulses is effective in defining the time during which nuclear displacements take place. A simplified equation, suitable for the pulsed-gradient experiment, is presented and solved for two different examples of systems showing restricted diffusion. A procedure for analyzing the data from pulsed-gradient measurements is suggested, and its merits are discussed. Suggestions are made of systems which may well be expected to show restricted, anisotropic diffusion or interesting flow properties.
A derivation is given of the effect of a time-dependent magnetic field gradient on the spin-echo experiment, particularly in the presence of spin diffusion. There are several reasons for preferring certain kinds of time-dependent magnetic field gradients to the more usual steady gradient. If the gradient is reduced during the rf pulses, H1 need not be particularly large; if the gradient is small at the time of the echo, the echo will be broad and its amplitude easy to measure. Both of these relaxations of restrictions on the measurement of diffusion coefficients by the spin-echo technique serve to extend its range of applicability. Furthermore, a pulsed gradient can be recommended when it is critical to define the precise time period over which diffusion is being measured.
The theoretical expression derived has been verified experimentally for several choices of time dependent magnetic field gradient. An apparatus is described suitable for the production of pulsed gradients with amplitudes as large as 100 G cm−1. The diffusion coefficient of dry glycerol at 26°±1°C has been found to be (2.5±0.2)×10−8 cm2 sec−1, a value smaller than can ordinarily be measured by the steady gradient method.
Nuclear magnetic resonance (NMR) spectroscopy was used to examine the behavior and extent of liquid water in postrigor-frozen
tissue of cod at temperatures below 0°C. A liquid-water phase persists in the tissue down to about -70°C; the extent of the
phase decreases rapidly between 0° and -10°C and slowly at lower temperatures. That the NMR absorption peak of the liquid
water increases in width, with decreasing temperature, suggests loss of mobility or structuring of the phase. A technique
for introducing geometrically uniform cores of muscle into the probe of the high-resolution spectrometer permits quantitative
determinations of liquid water.
NMR is a powerful tool in characterizing cross-link density in elastomers. Conventional NMR, however, restricts the sample geometry and does not allow measurements in presence of ferromagnetic materials. The concept of the MOUSE (mobile universal surface explorer) circumvents these restrictions. This surface sensitive method deals with rather inhomogeneous magnetic fields instead of the highly homogeneous fields normally used in NMR. Therefore, pulse sequences are reinvestigated with respect to their sensitivity towards residual dipolar coupling in elastomers. Examples for investigations of technical elastomers and correlations of NMR results with data from macroscopic mechanical measurements are presented.
Oilseed Residues: Simultaneous Determi-nation of Oil and Water Contents: Method using Pulsed NMR
- Iso Cd
ISO/CD 10632: Oilseed Residues: Simultaneous Determi-nation of Oil and Water Contents: Method using Pulsed NMR / June 1993.
Use of nu-clear magnetic proton relaxation to characteristic deep freezing of food
- V M Chernyshev
- A F Babkin
- T N Golovkina
V. M. Chernyshev, A. F. Babkin, T. N. Golovkina: Use of nu-clear magnetic proton relaxation to characteristic deep freezing of food. Cholodiln. Techn. 4 (1974) 30–35.
Rees: Pulsed NMR studies of restricted diffusion
- U J Packer
U. J. Packer, C. Rees: Pulsed NMR studies of restricted diffusion. J. Colloid Interface Sci. 10 (1972) 206–218.