Cj. Clark et Js. Macfall, MAGNETIC-RESONANCE-IMAGING OF PERSIMMON FRUIT (DIOSPYROS-KAKI) DURINGSTORAGE AT LOW-TEMPERATURE AND UNDER MODIFIED ATMOSPHERE, Postharvest biology and technology, 9(1), 1996, pp. 97-108
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.