Magnetic resonance imaging of browning development in 'Braeburn' apple during controlled-atmosphere storage under high CO2

Development of browning induced in 'Braeburn' apple (Malus xdomestica Borkh,) fruit by a damaging CO2 concentration was monitored weekly using magnetic resonance imaging (MRI) during a 4-week storage trial (0.5 degrees C, 2 kPa O-2/7 kPa CO2), Discrete patches of high-intensity signal, distributed randomly throughout the fruit, were observed in multislice images of samples after 2 weeks of storage; these patches were eventually confirmed as being sites of browning reactions after dissection at the end of the trial. Subsequently (weeks 3 and 4), signal intensity at sites of incipient damage increased and patches enlarged and coalesced. After 2 weeks of storage, the extent of affected tissue, averaged across all image slices, was 1.5%, increasing to 15.9% and 21.3% after 3 and 4 weeks. The average rate at which tissue damage spread in individual slices was 0.81 (range: 0-3.70) cm.d(-1) between weeks 2 and 3, declining to 0.32 (range: 0-1.55) cm(2).d(-1) in the final week. Tissue damage induced under these conditions did not spread at the same rate at all locations within individual fruit, nor was it preferentially located toward the stem or calyx ends of the fruit.