Nouvelle séquence 2D T1-T2 (IR-FID-CPMG) pour la quantification de la transformation des aliments

International audienceBy acquiring the FID signal in two-dimensional TD-NMR spectroscopy, it is possible to characterize mixtures or complex samples composed of solid and liquid phases. We have developed a new sequence for this purpose, called IR-FID-CPMG (1), making it possible to correlate spin-lattice T1 and spin-spin T2 relaxation times, including both liquid and solid phases in samples. We have demonstrated also the potential of a new algorithm for the 2D inverse Laplace transformation of IR-FID-CPMG data based on an adapted reconstruction of the maximum entropy method (2), combining the standard decreasing exponential decay function with an additional term drawn from Abragam’s FID function (3, 4). The results show that the proposed IR-FID-CPMG sequence and its related inversion model allow accurate characterization and quantification of both solid and liquid phases in multiphasic and compartmentalized systems, as for instance starchy products. As long as samples contain a moderate liquid content, this method can be applied to monitor structural changes during a particular process, such as heating. The implementation of FID acquisitions in 2D not only resolves short T2 relaxation times related to strong dipolar interactions in solid phases, but also considers the NMR signal of each component whatever its physical state, making possible the quantification of molecules using the area of the relaxation time peak. Another advantage of the IR-FID-CPMG method concerns its ability to distinguish between solid phases having different T1 relaxation times. It permits also to demonstrate some cross-relaxation phenomena. This is the case of many samples containing highly hydrophilic molecules like proteins or polysaccharides that display, with water, chemical exchanges and dipolar interactions

MR imaging of water sorption in starch-glycerol extrudates

International audienceStarch is widely used in controlled release systems because it is a high purity biocompatible and biodegradable material, which can be easily metabolized in the human body (1). The ingress of water in starch is therefore of great interest because of its relevance for the formulation of controlled release materials. Over the past decades, the magnetic resonance micro-imaging technique (MRµI) has proven to be an extremely reliable tool for measuring the water ingress during sorption and swelling of polymers used in a wide range of fields (food, pharmaceutical formulations, medical implants etc.) (2). However few studies present quantitative measurements when the sample of interest changes over time or in case of a long acquisition time. In this domain, two challenges have to be overcome: the introduction into the probe of a phantom as a reference signal and the guarantee that this signal is stable over the experiment duration while some conditions such as temperature and/or the moisture are varied. For that, we implemented a dedicated experimental set-up to generate a virtual phantom (ViP) signal in images (3). We will present its advantages and application to monitor the water sorption of a potato starch blend containing 20% glycerol that was shown to have interesting properties for biomedical applications. The relationships between the water rotational mobility (using T2 maps) and the water transport diffusion (using proton density maps) were analyzed. The rate constants for water diffusion and the starch swelling extracted from the proton density images showed that starch-glycerol blends exhibited a Fickian diffusion (type I) behavior at first step of the water uptake (400min). This kinetic revealed that the water concentration gradient was the driving force for its diffusion into the extrudate, while glycerol was released into the surrounding aqueous phase. With time, the water intake of the starch-glycerol extrudates was slower due to the competition between the crystallization of starch and penetration of the water (4)

Hydrothermal Changes of Starch Monitored by Combined NMR and DSC Methods

International audienceThe thermal, dynamic, and structural properties of wheat starch–water systems with different levels of water content (11, 35, 40, 42, 45, and 50%, wet basis) were investigated. 1H time domain nuclear magnetic resonance (TD-NMR) spectroscopy was used to interpret and quantify the water transfer and starch transformations in terms of water uptake, granule swelling, amylose leaching, and melting of starch polymers in relation to the different levels of water content. Complementary differential scanning calorimetry (DSC) experiments were performed to study the effects of water content on the degree of starch gelatinization. In particular, this twofold approach was applied to the first endotherm to study the mechanisms of gelatinization with a common heating range both in NMR and DSC. It was shown that the trend of the enthalpy changes in the first phase transition in starch–water (SW) mixtures was strongly correlated with the loss of solid content measured by NMR in the corresponding temperature range (55–70 °C). Based on the evolution of the relative amplitudes of T2, structural transformations of starch were shown to occur in both crystalline and amorphous regions within SW samples, supporting the fact that the amorphous phase of starch also plays a significant role in the phase transition of granules during gelatinization. This dynamic and hydrothermal approach provided the first NMR-based interpretation of the first endotherm measured by DSC

Temperature and water-associated changes of cereal starch monitored by TD-NMR and Microimaging

International audienceTime domain NMR (TD-NMR) method has been widely used to characterize starch, the major storage carbohydrate of cereals, as evidenced by the numerous relaxometry and diffusometry studies available in literature [Kovrlija, R. and Rondeau-Mouro C. Food Chemistry, 2017]. When starch is heated and then cooled in the presence of water, it undergoes a series of changes known as swelling, gelatinization and retrogradation that induce variations in water distribution, in starch structure and interactions between them. These biochemical transformations can be investigated and quantified using TD-NMR, also convenient for the continuous monitoring of products during processing up to their final structure. Magnetic Resonance microImaging (MRµI) is a complementary technique that can be applied to investigate, with a spatial resolution, the water penetration in cross-linked starch blends and cereal foodstuffs. NMR and MRI techniques could help cereal scientists to better understand the behaviors of macro-molecules in baked products and their interaction with each other and water, and to make products with better quality and shelf-life. This presentation will be focused on the applications of these two methods for characterizing at molecular or millimetric scales, cereal starch-water systems under hydration and/or heating and cooling. We will show TD-NMR results on starch-water systems and dough at various water levels (40-55% wb). Relaxometry measures permitted to simultaneously quantify water transfers and starch changes induced by a thermal processing between 20 and 90°C (10°C steps) followed by a cooling at ambient temperature. In another hand, the application of MRµI to monitor the water sorption kinetics in starch-glycerol extrudates allowed going ahead in the multi-scale approaches by distinguishing between various water diffusion behavior (Fickian or case II case), in relation with different physical and mechanical properties of starch-based products

Suivi multi-échelle par RMN des transferts d'eau dans des produits à base d'amidon

International audienceNuclear magnetic resonance spectroscopy (NMR) and magnetic resonance imaging (MRI) are non-invasive and non-destructive methods giving access to the water mobility in porous and heterogeneous media at various scales. The first one is based on the measurement of relaxation times (T1 and T2) related to the molecular mobility more or less impacted by the sample composition, its microstructure, chemical and diffusional exchanges between protons and molecules, respectively 1. In this context, the 2D NMR, based on a joint observation of T1 and T2, has been shown to be very efficient to monitor the water transfers and the starch changes when starchy products were heated 2. A complementary approach consists in using MRI (or microimaging) to study swelling and water diffusion in hydrophilic samples. This is a perfect tool to follow the evolution of the sample’s shape and the concentration changes due to water uptake. The technique can be easily used to monitor simultaneously different regions of interest in the object and qualitative/quantitative results can be obtained. The application of this method to monitor the water sorption kinetics in a starch-based sample will be presented. The results indicate that water profiles in the sample can be used to estimate, on the basis of Crank equations 3, the water diffusion coefficient along few millimeters

Relaxométrie par RMN et IRM de produits amylacés

International audienceNuclear magnetic resonance spectroscopy (NMR) and magnetic resonance imaging (MRI) are non-invasive and non-destructive methods giving access to the water mobility in porous and heterogeneous media at various scales. The ingress of water in starchy products is of interest because it has relevance to the storage, drying, enzymatic activities and processing of starch-based materials, but also for the formulation of controlled release materials. NMR Relaxometry (in low-field NMR, LF-NMR) is based on the measurement of relaxation times (T1 and T2) related to the molecular motions more or less impacted by the sample composition, its microstructure, chemical and diffusional exchanges between proton pools. In this context, the 2D LF-NMR, based on a joint observation of T1 and T2 relaxation times, has been shown to be very efficient to monitor the water transfers and the starch structural changes when the sample was heated. We applied and improved this method to enhance our understanding of water distribution and starch gelatinization during the thermal processing of starch in model systems and dough (1-4). MRI is a complementary technic widely used for medical diagnosis, but since several years it has been developed to investigate the solvent penetration in cross-linked polymers and pharmaceutical excipients (5). The application of this method to monitor the water sorption kinetics in a starch-based sample will be presented (6). The results indicate that water profiles in the sample can be used to estimate, on the basis of Crank equations (7), the water diffusion coefficient along few millimeters. 1. Rondeau-Mouro C, Cambert M, Kovrlija R, Musse M, Lucas T, Mariette F. Temperature-Associated Proton Dynamics in Wheat Starch-Based Model Systems and Wheat Flour Dough Evaluated by NMR. Food and Bioprocess Technology. 2015;8(4):777-90. 2. Rondeau-Mouro C, Kovrlija R, Van Steenberge E, Moussaoui S. Two dimensional IR-FID-CPMG acquisition and adaptation of a maximum entropy reconstruction. Journal of Magnetic Resonance. 2016;265:16-24. 3. Kovrlija R, Rondeau-Mouro C. NMR proton dynamics and DSC enthalpic transitions in starch-water mixtures. Food and Bioprocess Technology. 2017;in press. 4. Kovrlija R, Rondeau-Mouro C. Hydrothermal changes in wheat starch monitored by two-dimensional NMR. Food chemistry. 2017;214:412-22. 5. Baille WE, Malveau C, Zhu XX, Marchessault RH. NMR Imaging of high-amylose starch tablets. 1. Swelling and water uptake. Biomacromolecules. 2002;3(1):214-8. 6. Rondeau-Mouro C, Kovrlija R, Gambarota G, Saint-Jalmes H. μ-ViP: Customized virtual phantom for quantitative magnetic resonance micro-imaging at high magnetic field. Journal of Magnetic Resonance. 2017;275:73-9. 7. Crank J. The mathematics of diffusion. Clarendon Oxford. 1975

Etudes en RMN à bas champ d'amidons de différentes origines botaniques : effets des transformations hydro-thermiques et du stockage

International audienceThe effects of starch origin on water migration and starch transformation were investigated using one- and two-dimensional TD-NMR methods. The quantification of T1 and especially of T2 relaxation times during thermal treatment enabled their interpretation relative to the sorption, gelatinization and retrogradation phenomena of starches in the presence of water, in a level close to that used for bread making (50%, wet basis). Comparison between native wheat, waxy corn and potato starches made possible to link relaxation variations to starch structure and properties as crystallinity, granule size, polymorphism, amylopectin content and water-binding capacity all along heating, cooling and storage processes

Rétrogradation de l'amidon étudiée par RMN 2D

International audienceStarch retrogradation has been extensively investigated mainly due to its detrimental effect on the sensory and storage qualities of many starchy foods; however, this phenomenon has proved to be desirable for some of them (1). The association of linear amylose molecules occurs rapidly in the first stage of retrogradation, whereas slow increase in the degree of crystallinity and gel firmness, exudation of water (syneresis), and the appearance of B-type crystallites should be ascribed to the long-term amylopectin retrogradation. The time-domain Nuclear Magnetic Resonance (TD-NMR) allows obtaining qualitative and quantitative description of these processes. This method was commonly used to study complex wheat starch-based systems, such as bread (2, 3). On the other hand, the retrogradation of starches having different origins than wheat was rarely investigated (4). Therefore, the potato starch, waxy maize starch, and wheat starch, all hydrated at 50% (wet basis), were heated from 20 to 90°C, cooled to 20°C, and subsequently stored for 3, 7, and 14 days at the same temperature in order to investigate and compare their retrogradation ability. These three types of starch were chosen due to their different composition (amylose/amylopectin ratio) and crystalline unit packing (A- and B-type X-ray diffraction patterns). The NMR signal (20 MHz) was always acquired at 20°C, in one dimension (T1 and T2) as well as in two dimensions (T1-T2), at the onset of heating, after the cooling step, and during the storage. NMR measurements including the novel 2D approach using IR-FID-CPMG sequence (5), were interpreted in terms of changes in the starch and water dynamics in relation with solid content changes due to starch retrogradation

Changements de structure associées aux variations de température et d'hydratation des produits céréaliers suivis par RMN à bas champ

International audienceBased on spin-spin T2 relaxation time measurements, the time-domain NMR (TD-NMR) spectroscopy has been used to provide relevant information on the water and biopolymer motion and transfer in bread. This technique permits to characterize molecular interaction and transformations in a non-invasive and non-destructive way, in real time during a process (heating, freezing, hydration ...). In bread, proteins of gluten when hydrated form a viscous mass that confers to the dough, structure, viscosity, mixing tolerance and gas holding ability. On the other hand, starch, in presence of water and increasing temperature, undergoes a series of changes known as swelling, gelatinization and retrogradation that induce variations in water distribution, in starch structure and interactions between them. Our studies aims at understanding and ranking the contribution of these biochemical transformations that contribute to the crumb structure and the textural properties of bread made with cereal flour or a gluten free mix. The water transfers and the extent of starch gelatinization in dough and crumb were studied by TD-NMR during and after the heating/cooling process of dough at various water levels. Preliminary fast field cycling NMR experiments make it possible to envisage further works in order to understand the role of water in the formation of bread crumbs

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

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