MRI study of tomato dehydration

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Quantitative MRI analysis of structural changes in tomato tissues resulting from dehydration

International audienceA quantitative magnetic resonance imaging (MRI) analysis at 1.5T of the effects of different dehydration regimes on transverse relaxation parameters measured in tomato tissue is presented. Multi-exponential T-2 maps have been estimated for the first time, providing access to spatialized microstructural information at voxel scale. The objective was to provide a better understanding of the changes in the multi-exponential transverse relaxation parameters induced by dehydration in tomato tissues and to unravel the effects of microstructure and composition on relaxation parameters. The results led to the hypothesis that the multi-exponential relaxation signal reflects cell compartmentation and tissue heterogeneity, even at the voxel scale. Multi-exponential relaxation times provided information about water loss from specific cell compartments and seem to indicate that the dehydration process mainly affects large cells. By contrast, total signal intensity showed no sensitivity to variations in water content in the range investigated in the present study (between 95% [fresh tissue] and 90% [after dehydration]). The variation in relaxation times resulting from water loss was due to both changes in solute concentration and compartment size. The comparative analysis of the two contrasted tissues in terms of microporosity demonstrated that magnetic susceptibility effects, caused by the presence of air in the placenta tissue, significantly impact the effective relaxation and might be the dominant effect in the variations observed in relaxation times in this tissue

Multi-scales investigation of eyes in Swiss-type cheese

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Multi-scale investigation of eyes in semi-hard cheese

Semi-hard cheeses can be characterized by their bubbles, or "eyes", whose growth mechanisms have generally been explained empirically. The objective was to design a relevant multi-scale investigation strategy in order to determine if there is a relationship between eye growth kinetics and surrounding cheese microstructure. Magnetic resonance imaging provided the spatial distribution and growth kinetics of individual eyes during ripening. The eyes were smaller, less numerous and growing slower under the rind than in the center. Three microscopic techniques were combined to study cheese microstructure. Light microscopy showed horizontal curd grains with junctions unchanged during ripening. Confocal laser scanning microscopy revealed fat globules embedded in a continuous protein network in both zones and ages. Scanning electron microscopy showed a comparable porous protein network for all samples. No microstructure difference was found on the basis of sample location or age, but this study showed that bacteria repartition could participate to the opening gradient. Industrial relevance: Achieving a monitoring of eye growth and of the evolution of the surrounding microstructure would allow a better understanding of the growth mechanisms, which would have several advantages: The cheese-making process would be improved by anticipating what could be the influence of a recipe or process change on eye development, especially as eyes are important quality indicators of cheeses. It would also be interesting to master the number, size and shape of eyes, and especially to achieve a homogeneous repartition inside cheeses. It is also of high interest to avoid cracks and slits in cheese. (C) 2013 Elsevier Ltd. All rights reserved

MRI investigation of internal defects in potato tubers with particular attention to rust spots induced by water stress

International audiencePotato quality is a major concern for both producers and customers. However, potato tubers are affected by various forms of internal damage with no external symptoms, leading to substantial economic losses. MRI was used as a non-invasive and quantitative method to evaluate internal defects in potato tubers and their evolution during storage. Rust spots, induced by water stress, were considered in particular. To this end, potato plants were cultivated both in the field and in pots and their water uptake was controlled. Following harvest and throughout the storage period, 3D images of tubers were recorded on a 1.5 T MRI scanner using a fast spin echo sequence. In parallel, the multi-exponential transverse relaxation times (T2) of the tubers were mapped in order to provide information on changes in water status and distribution at the subcellular level in rust spots and in healthy perimedullary regions. The occurrence of rust spots correlated with water conditions in greenhouse where water intake was carefully controlled. The number and individual volume of rust spots did not change during storage period, but they significantly increased with tuber size. Bi-exponential transverse relaxation revealed differences between healthy and damaged tissue

Inflation, squeezing and collapse in wheat flour dough during baking: Effects of flour quality and oven temperature

International audienceAn existing method to assess variations in local gas fraction (Wagner et al. 2008, J. Cereal Sci. 27(4), 577–585) was further developed and successfully adapted to real bakery products (pan bread, baguette). Local inflation was found to be temperature-dependent for as long as cells remained closed. Collapse in unbalanced dough was monitored by MRI, showing that local inflation at the core occurred simultaneously with a pronounced overall decrease in the dough section. Maximal inflation in unbalanced dough is maximal while crust is still deformable (not set)did not coincide with crust setting but occurred when core inflation counterbalanced the collapse of the peripheral dough layers. Crust setting occurred later, during the overall decrease in the dough section. The formation of a rigid shell halted collapse and led to a slope reduction in the dough-section decrease which then continued at the pace of the shrinkage of the porous structure upon dehydration. Squeezing occurred in the peripheral crumb layers when the rapid expansion of the dough core encountered the limitations in overall expansion introduced by crust setting; consistent with this view, squeezing started when the overall rate of dough inflation slowed (causing a break in the slope), and finished at the cessation of core inflation. The slow rate of decrease in overall dough area (<1% per min) was associated with the downward and upward displacement of the upper and lower dough surfaces respectively and was assigned to dehydration-induced shrinkage. Calculations of local strain and strain rates confirmed a preponderance of large strains (0.20-0.30) and low strain rates whether in extension or compression (10-3 s-1)

Multiphoton microscopy is a nondestructive label-free approach to investigate the 3D structure of gas cell walls in bread dough

Abstract During the different steps of bread-making, changes in the microstructure of the dough, particularly in the gas cell walls (GCW), have a major influence on the final bread crumb texture. Investigation of the spatial conformation of GCWs is still a challenge because it requires both high resolutions and 3D depth imaging. The originality of the present work lies in the use of label-free non-destructive multiphoton microscopy (NLOM) to image the 3D structure of GCWs, shedding light on their behavior and organization in wheat bread dough. We demonstrated that second and third harmonic generation (SHG, THG) allow imaging, respectively, of starch granules and interfaces in bread dough, while the gluten matrix was detected via two-photon excitation fluorescence (TPEF). Last, a distinction between the gluten network and starch granules was achieved using gluten endogenous fluorescence (EF) imaging, while the position, size, and 3D orientation of starch granules in GCWs were determined from harmonic imaging, made possible by the acquisition of backward and forward SHG with linear polarization. These innovative experiments highlight the strengths of NLOM for a label-free characterization of bread dough microstructure for the first time, in order to understand the role of starch granules in dough stabilization

Tissue characterization of potato tubers using localized MRI T2 Relaxometry

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Tissue characterization of potato tubers using localized MRI T2 Relaxometry

International audienc

Characterization of the effects of water shortage on four potato varieties by NMR techniques

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