NMR imaging of air spaces and metabolites in fruit and vegetables

This chapter deals with the principles and the applications of magnetic resonance imaging (MRI) for assessment of the distribution and of the amount of intercellular gas-filled spaces and major metabolites in fruit and vegetable tissues. Combining this information with measurements of water characteristics could enable the use of MRI in an integrative approach to plant characterization. In MRI, the presence of gas-filled intercellular spaces in plant tissues impacts the NMR relaxation behavior of water molecules because gas and water have different magnetic susceptibilities. This phenomenon can be exploited for the noninvasive detection of certain physiological disorders in fruit and vegetable tissues or for quantification of the spatial distribution of apparent microporosity. On the other hand, the amount and the distribution of major metabolites (sugars, starch, lipids, etc.) can be accessed by MRI using approaches based on differences in relaxation times or on chemical shift between water and metabolites protons. Here we provide an overview of the theoretical aspects of MRI methods and a description of different approaches. The imaging protocols for specific applications for both air space and metabolite imaging are discussed with respect to their application to fruits and vegetables.