MAGNETIC-RESONANCE-IMAGING OF PERSIMMON FRUIT (DIOSPYROS-KAKI) DURINGSTORAGE AT LOW-TEMPERATURE AND UNDER MODIFIED ATMOSPHERE

Effects of time and storage atmosphere on relaxation properties in per simmon fruit (Diospyros kaki cv Fuyu) were investigated by nuclear mag netic resonance (NMR) imaging during the five weeks following commerci al harvest. There were two treatments (n = 4): one in which fruit were hermetically sealed in individual polyethylene bags (modified atmosph ere or MA treatment), and another sealed in individual perforated bags (control). Fruit were stored at 7 degrees C for 4 weeks (conditions c onducive to development of chilling-injury), before being removed to 2 0 degrees C for 3 days to simulate poststorage shelf conditions. Every week, and at the end of the shelf-life period, a series of H-1 NMR im ages of median transverse and longitudinal planes were acquired from e ach fruit for calculation of spin-lattice (T-1) and spin-spin (T-2) re laxation times. Relaxation times associated with the flesh, vasculatur e and locules in transverse sections, and flesh from basal, median and distal regions of longitudinal sections, were significantly shorter i n MA-treated fruit, although no T-2 treatment difference was noted wit h vasculature. MA-treated fruit were further distinguished from contro ls in that all tissues exhibited a sharp increase in T-1 (but not T-2) relaxation between the second and third weeks in cold storage. Within a treatment, T-1 times in flesh and locules were similar (ca. 1120 ms ), and shortest in vascular tissue (1036 ms). T-2 was a more sensitive indicator of tissue type (mean values of 71, 101 and 116 ms in the va sculature, flesh and locules of MA-treated fruit, respectively), than T-1. However the relative ranking of flesh and locule tissues was time -dependent. There was no gradient in relaxation times between basal, m edian and distal regions of the fruit. Incipient stages of chilling-in jury development were unable to be identified either by visual inspect ion of time-course images, or variation in relaxation properties. Our observations do indicate, however, that relaxation properties in fruit were strongly influenced by MA conditions. Increased concentrations o f soluble metabolites arising from reduced respiration in MA-treated f ruit is a possible mechanism consistent with these results, but not re moval of a paramagnetic species like O-2, where T-1 values would be pr edicted to increase.