Study of tomato maturity using nuclear magnetic resonance relaxometry and imaging

Tomatoes experience complex sequential physiological and structural changes during ripening. This study explores this process by using proton Nuclear Magnetic Resonance (NMR) Relaxometry to investigate changes in tomato fruit during maturation and detect tomato maturity with Magnetic Resonance Imaging (MRI). Multiple T₂ relaxation components were observed in T₂ relaxation measurement of excised pericarp disks. Three relaxation components were resolved from the decay, which were assigned to water in vacuole, cytoplasm, and cell wall, respectively. The T₂ of the vacuole water decreased gradually as tomato fruit turned red. The T₂ of both cytoplasm and cell wall water reached a maximum at light red stage, and showed a considerable decrease at red stage. The vacuole showed a steady increase in its relative water content as the fruit ripened. The pattern of changes in relative water content of cytoplasm and cell wall is more complicated, but their values tend to decrease towards the late stages. The changes in T₂ relaxation behaviour revealed the variations in the water mobility and distribution at subcellular level as tomato ripened. In addition, tomato fruit were scanned using seven imaging sequences. Partial least square-discriminant analysis was carried out on the signal intensity of the pericarp region in the images acquired by the seven imaging sequences. About 86% of the red fruit and 91% non-red fruit were classified correctly. The major cause of the classification error is the subtle difference between light red and red fruit.