Caractérisation de la microstructure spatiale de la pomme en lien avec ses propriétés mécaniques par des méthodes quantitatives d’IRM

(trad auto)The mechanical properties of the apple pericarp depend on a multitude of factors. The dry matter, divided between insoluble fraction (walls) and soluble fraction, the condition of the water and its distribution within the cell, the fraction of air between the cells, and their size and organization are involved. The state of water and its distribution have been poorly studied and quantitative MRI is a tool of choice for non-destructive measurements. We have used the multi-exponential MRI relaxation signal of the fruit in an original way to extract the signal from different aqueous fractions. Studying the variations in amplitude and relaxation time of these fractions in fruits of variable size has made it possible to characterize the heterogeneity of the fruit and the influence of cell size on the MRI signal. A multi-instrumental approach applied to the parenchyma during cold storage then made it possible to compare its viscoelastic properties (dynamic mechanical analysis) with its water distribution and porosity (MRI) and the size, shape (macro-vision) and composition (determination of soluble sugars, hemicelluloses and parietal pectins) of its cells. Finally, the MRI signal was studied on all fruit tissues at 1 month and 6 months of storage. This work made it possible to demonstrate the interest of the MRI approach to describe the heterogeneity of the fruit on criteria of water condition and water distribution and porosity, to specify certain mechanisms involved in NMR relaxation and to prioritize the various structural and compositional parameters involved in the mechanical properties of tissues.Les propriétés mécaniques du péricarpe de la pomme dépendent d’une multitude de facteurs. Sont impliqués la matière sèche, répartie entre fraction insoluble (parois) et fraction soluble, l’état de l’eau et sa répartition au sein de la cellule, la fraction d’air entre les cellules, et leur taille et organisation. L’état de l’eau et sa répartition n’ont été que peu étudiés et l’IRM quantitative est un outil de choix pour réaliser ces mesures de façon non-destructive. Nous avons de façon originale exploité le signal IRM multi-exponentiel de relaxation du fruit pour en extraire le signal de différentes fractions aqueuses. Etudier les variations d’amplitude et de temps de relaxation de ces fractions dans des fruits de calibre variable a permis de caractériser l’hétérogénéité du fruit et l’influence de la taille des cellules sur le signal IRM. Une approche multi-instrumentale appliquée au parenchyme durant un stockage au froid a ensuite permis de mettre en regard ses propriétés viscoélastiques (analyse mécanique dynamique) avec sa répartition hydrique et sa porosité (IRM) et la taille, la forme (macro-vision) et la composition (dosage des sucres solubles, hémicelluloses et pectines pariétales) de ses cellules. Enfin, le signal IRM a été étudié sur l’ensemble des tissus du fruit à 1 mois et 6 mois de stockage. Ce travail a permis de démontrer l’intérêt de l’approche IRM pour décrire l’hétérogénéité du fruit sur des critères d’état de l’eau et de répartition de l’eau et de la porosité, de préciser certains mécanismes impliqués dans la relaxation RMN et de hiérarchiser les différents paramètres de structure et de composition impliqués dans les propriétés mécaniques des tissus

Monitoring the apple texture during storage using quantitative MRI

International audienceMicrostructural characteristics of fruit tissues at the origin of texture changes are difficult to access instrumentally. Recent developments in quantitative MRI allow studying microstructure via localized measurements of multi-exponential T2 reflecting water status and distribution at the subcellular level [1] and the apparent microporosity [2]. In the present study, these methods were applied on six apple cultivars using a 1.5T clinical MRI scanner. Additionally, mechanical (storage modulus (E’) and dampening factor (Tan∂)) and biochemical (water, free sugar and alcohol-insoluble solid contents) analyses were performed. The aim was to investigate the link between microporosity, water distribution and composition and mechanical properties characterizing fruit texture quality. Four of six genotypes studied were followed during 3-month storage at 4 °C. In the general way, six apple genotypes were divided according to PCA analysis into two groups; the first one containing 3 genotypes characterized by higher T22, T23 and E’ and the second one 3 genotypes with higher microporosity, Tan∂ and T21-associated amplitude. As apples from the second group are known to be mealy cultivars, the results agreed with previously reported relationship between T2 and apple mealiness [3] and reveal a link between mealiness and Tan∂. Apples evolved only slightly in terms of both the MRI and mechanical parameters during the considered storage period

Assessment of apple texture by quantitative MRI

International audienceQuantitative MRI is an appropriate tool to study microstructure of intact fruit. It allows accessing multi-exponential transverse relaxation times (T2) [1] providing insights on water status and distribution at the subcellular level and apparent microporosity maps providing information about gas distribution [2]. In this study, MRI measurements were carried out on several apple cultivars. Mechanical and biochemical analysis were also performed in order to investigate the contributions of microstructure and composition to mechanical properties characterizing fruit texture quality. Cultivars studied were Granny-Smith, Ariane, Fuji, EC (experimental cultivar), Florina and Rome-Beauty;. MRI multi-exponential T2 and porosity measurements were first carried out on a 1.5T clinical scanner. Samples for destructive analysis were then extracted from outer parenchyma. Storage modulus (E’) and dampening factor (Tan∂) of the sample were measured by Dynamic Mechanical Analysis. Water and free sugar contents and alcohol-insoluble solids were measured for all fruit. Results were analyzed using PCA and ANOVA tests. The T2 decay in all fruit was well fitted by a tri-exponential curve (T21~25ms; T22~125ms and T23~500ms). Both T2 and microporosity maps revealed parenchyma heterogeneity. PCA of combined compositional, mechanical and NMR data from the outer parenchyma tissue region showed that 6 apple genotypes were divided into two groups: G1- Granny-Smith, Ariane and Fuji characterized by higher T22, T23 and E’ and G2- Florina, Rome-Beauty and EC with higher microporosity, Tan∂ and T21-associated amplitude. Apple flesh rigidity (~E’) was inversely related to microporosity. Moreover, Rome-Beauty and Florina from the G2 are known to be mealy cultivar. The results agree with previously reported relationship between T2 and apple mealiness [3] and reveal a link between mealiness and Tan∂. By uncovering clear relations between apple parenchyma tissue microstructure and water status with fruit texture, quantitative MRI represents a highly valuable tool for fruit quality assessment

Characterisation of apple microstructure using quantitative MRI

International audienceIntroduction Quantitative Magnetic Resonance Imaging is an appropriate non-destructive tool to study plants microstructure. Recent developments allow accessing multi-exponential relaxation of water protons, furnishing data about water repartition inside cells. Microporosity in fruit tissues can also be estimated by MRI, providing additional information about gas distribution. The present study aims to provide a better understanding of the microstructure and micro-heterogeneities of apple, for the first time by applying multi-exponential relaxation models to spatially resolved MRI data. Experiments were performed on fruits of different size combining MRI multi-exponential T2 and microporosity quantification with histological measurements. Methods Experiments were performed on 7 small (~130g) and 7 big (~300g) apples, variety Jonagored. MRI measurements were carried out on a 1.5T MRI scanner (Avanto, Siemens). The 5mm median planes of fruit were imaged with a pixel size=1.19mm² and a TR=10s. T2 was obtained from a 512echo MSE sequence with ΔTE=7.1ms. T2*, used with T2 for porosity estimation, was obtained from GE sequences with TE1=2.77ms and ΔTE=1.61ms. Analyses were focused on the inner cortex, near the core and on the outer cortex, near the cuticle. Cell size distribution was estimated on same samples from macrovision images using an erosion/dilation method. Results Apple T2 decay was well fitted by a tri-exponential decay curve: T2 were about 50, 150 and 450ms and relative intensities about 5, 20 and 75% respectively. T2 measurements in outer cortex of small and big apples showed variations only for the longest T2 component from 423±25ms to 469±20ms respectively; relative intensities being similar (76±1%). Cell size distributions, obtained by macrovision, showed larger cells in big apples thus linking cell size to T2 relaxation time. Microporosity also increased from 22±4% for small fruits to 28±1% for big apples. Variations between inner and outer cortex were also studied. Microporosity increased from 25±3% (inner) to 34±4% (outer) and the longest T2 relaxation time was 454±21ms in the inner cortex and 512±30ms in the outer cortex. Using size-contrasted fruits permitted to highlight cell size influence on multi-T2 relaxation time. In apple cortex, longest T2 relaxation time was found to increase with distance to the core. Unexpectedly, T2 time increased while microporosity increased showing other factors affecting T2 remain to be investigated

Analysis of the dynamic mechanical properties of apple tissue and relationships with the intracellular water status, gas distribution, histological properties and chemical composition

International audienceMechanical properties of fruit depend on many parameters, including microporosity, cell characteristics and cell wall composition/structure. Recent developments in quantitative MRI provide the possibility of studying fruit through local measurements of multi-exponential T2 reflecting water status and distribution at the subcellular level, and apparent microporosity. In the present study, dynamic mechanical analysis provided Young's modulus and the damping factor, reflecting elastic and viscous properties of apple tissue, respectively. These measurements were compared to quantitative MRI measurements, biochemical analysis (water, free sugar and alcohol-insoluble solid contents, cell wall composition) and histological measurements, all performed on apple parenchyma tissue. The aim was to investigate the respective contributions of microporosity, intracellular water status and distribution, and chemical composition to mechanical properties characterizing fruit texture quality. Correlations between the measurements were studied for six apple cultivars with storage times varying from one to six months. A general behavior pattern independent of cultivar and storage time provided greater understanding of the parameters involved in mechanical properties. Cell wall arabinose composition and water status associated with the vacuole were correlated with Young's modulus, the xylose and hemicellulose compositions were correlated with the damping factor and the relative amount of water attributed to the cytoplasm and the apparent microporosity of the samples were correlated with both the damping factor and Young's modulus. Modification of the water pool attributed to the extracellular water/cell wall was shown to be involved in softening of the tissue. Comparison of the different measurements showed that variations in relaxation times were not explained by the water content, indicating that other phenomena such as membrane permeability, vacuole size and/or solute composition were predominant in the relaxation mechanism. A correlation between water pools attributed to the vacuole and cytoplasm evidenced water exchange occurring between the two compartments. © 2015 Elsevier B.V

Investigation of apple parenchyma microstructure using MRI multi-exponential T2 relaxation and microporosity measurements

International audienceIntroduction Quantitative Magnetic Resonance Imaging is an appropriate non-destructive tool to study fruit microstructure [1]. Recent developments [2] allow accessing spatially resolved multi-exponential relaxation of water protons in the intact fruit, providing insights on water status and distribution at the subcellular level. Microporosity distribution in fruit tissues can also be estimated by MRI [3], offering additional information about gas distribution. For the first time, MRI multi-exponential T2 and apparent microporosity were used to investigate the effects of fruit heterogeneity and cell size for different apple cultivars. The MRI data were related to histological measurements. The general objective was to provide a multi-scale approach for apple tissue characterization. Material & Methods Experiments were performed 2-weeks after harvest on Granny Smith, Ariane, Fuji apples and an experimental cultivar (EC). Apples were calibrated as 3 groups: c1, about 120 cm3, c2 about xx cm3 and c3, about 290 cm3. MRI measurements were carried out on a 1.5T MRI scanner (Avanto, Siemens). The 5 mm median planes of fruit were imaged with a pixel size = 1.19 mm² and a TR = 10 s. T2 was obtained from a 512-echoes MSE sequence with ΔTE = 7.1 ms. T2*, used with T2 for microporosity estimation, was obtained from GE sequences with TE1 = 2.77 ms and ΔTE = 1.61 ms. Cell size distribution was estimated on same samples from macrovision images using an erosion/dilation method [4]. Results Apple T2 decay was well fitted by a tri-exponential decay curve with T2 about 15-26 ms, 85-135 ms and 360-550 ms and associated relative intensities about 10, 20 and 70 % respectively. The study of heterogeneity of parenchyma revealed that from outer (near the cuticle) to inner (near the core) regions, relaxation times decreased up to 20% and subcellular water distribution was slightly different. In contrast, microporosity was shown to increase of up to 28 % (see fig. 1). T2 measurements of Fuji apple s of calibers c1 and c3 showed variations only for the longest vacuolar T2 component from 423 ± 25 ms to 469 ± 20 ms, respectively. Cell size distributions, obtained by macrovision, showed larger cells in big apples thus linking cell size to T2 relaxation time. Microporosity increased from 33 ± 3% for small fruits to 39 ± 2 % for big apples. Differences between cultivars of the same caliber were observed. For example, EC had higher porosity and lower relaxation times and Granny Smith had a less heterogeneous parenchyma than other cultivars. Size-contrasted fruits permitted to highlight cell size influence on multi-T2 relaxation time. In apple cortex, T2 relaxation time increased with distance to the core even if apparent microporosity increased. This work showed that MRI can differentiate apple cultivars according to their T2 and microporosity spatial distribution. References [1] Van As, H. and J. van Duynhoven, Journal of Magnetic Resonance, 2013. 229: p. 25-34.. [2] Adriaensen H, et al, Magnetic Resonance Imaging, 2013. [3] Musse, M., et al., Magnetic Resonance Imaging, 2010. 28(10): p. 1525-34 [4] Devaux, M.-F., et al., Postharvest Biology and Technology, 2008. 47(2): p. 199-20

Quantitatiovr MRI in the assessment of apple texture

International audienceMicrostructural characteristics at the basis of fleshy fruit texture variations are difficult to assess instrumentally. New developments in quantitative MRI allow localizing water status and distribution at the subcellular level [1] and mapping the apparent microporosity [2] in fruit. In this study, these methods were used to assess the contributions of these variables in Granny-Smith (GS), Ariane (AR), Fuji (FU), EC (experimental cultivar), Florina (FL) and Rome-Beauty (RB) apple texture along with mechanical and cell wall chemical analysis. MRI measurements were carried out on a 1.5T clinical scanner. Storage modulus (E’) and dampening factor (Tan∂) of apple parenchyma samples were measured by Dynamic Mechanical Analysis. Water, free sugar and alcohol-insoluble solids were quantified and cell wall polysaccharides characterized. Results were analyzed using PCA and ANOVA tests. The T2 relaxation decay was fitted by a tri-exponential curve (T21~25ms; T22~125ms and T23~500ms). Both T2 and microporosity maps revealed parenchyma heterogeneity. PCA allowed classifying apple varieties into two groups: G1 (GS, AR and FU) characterized by higher T22, T23 and E’ and G2 (FL, RB and EC) with higher microporosity, Tan∂ and T21-associated amplitude. Apple flesh rigidity (~E’) was inversely related to microporosity. RB and FL from G2, defined as mealy fruits, had T2 agreeing with those reported for this texture defect [3] and revealed a link between mealiness and Tan∂. The cell wall polysaccharide chemistry underlying these characteristics will be presented. The clear relations established by quantitative MRI between parenchyma tissue microporosity and water status with apple texture make this technique a highly valuable non-destructive tool for fruit quality assessment. [1] Adriaensen et.al, Magn Reson Imaging, DOI:10.1016/j.mri.2013.02.004 (2013); [2] Musse et al., Magn Reson Imaging, 28, 1525-34 (2010); [3] Barreiro et al., Appl Magn Reson 22, 387-400 (2002

MRI study of apple parenchyma microstructure – link with mechanical properties

International audienceQuantitative Magnetic Resonance Imaging (MRI) is an appropriate non-destructive tool for studying plants. The transverse relaxation time (T2), which is related to the water status in samples (i.e. water content, water mobility and interaction between water and macromolecules), was revealed relevant for studying plant microstructure. Recent developments [1] allow accessing multi-exponential transverse relaxation of water protons, providing data about water repartition and status at subcellular level. Apparent microporosity in fruit tissues can also be estimated by MRI [2], providing additional information about gas distribution. The first aim of this study was to characterise the heterogeneity of apple fruit tissues according to cell water status and gas distribution. MRI and histological macrovision measurements were performed on fruits from three different cultivars; fruits of different sizes were selected for each cultivar to provide tissues with cells of different dimensions. This study highlighted the heterogeneity of apple tissues in terms of relaxation parameters, apparent microporosity and cell morphology. Variations in cell size partially explained the different T2 observed. The second aim of the study was to investigate the link between cell water characteristics, apparent tissue microporosity and biochemical analyses and mechanical properties reflecting fruit texture quality. Correlations between the measurements were studied for six apple cultivars with storage times varying from one to six months. A general behaviour patterns independent of cultivar and storage time were demonstrated, providing understanding of the parameters involved in mechanical properties

Assessment of apple texture by quantitative MRI

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