(trad auto)Characterization of the spatial microstructure of apples in relation to their mechanical properties by quantitative MRI methods

Overview & Synopsis

(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.