Assessment of TD-NMR and Quantitative MRI Methods to Investigate the Apple Transformation Processes Used in the Cider-Making Technology Check Access

NMR relaxation parameters as spin-spin (T₂) and spin-lattice (T₁) relaxation times have been shown to be very relevant to study the microstructure of plant tissues. Magnetic Resonance Imaging (MRI) has also been used to study plant tissues. This non-destructive and non-invasive technique allows the recording of images. Many MRI studies have focused on the quality and defects of fruits. The combination of NMR and MRI technics is an efficient way to monitor agricultural practices and industrial processes like ripening, cooking or freezing. Indeed the association of these two methods enables a study at different scales of the structure and the tissue integrity and seems to be convenient for the study of juice extraction processes. The aim of this study was to understand the determinants that contribute to the extraction yield optimization. TD-NMR relaxometry and quantitative MRI were performed to characterize the impact of the grinding and pressing processes on apple tissues. The authors demonstrated here that TD-NMR and MRI are reliable tools providing information about the heterogeneous structure of apple parenchyma tissue as well as the subcellular water distribution at the origin of the multi-exponential T₂ signal measured. The results also indicated that complementary investigations should be necessary using biochemical quantitative analyses and mechanical tests to understand the water distributions in pressed materials.