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 magneti c resonance imaging (MRI) during a 4-week storage trial (0.5 degrees C, 2 k Pa O-2/7 kPa CO2), Discrete patches of high-intensity signal, distributed r andomly 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. Subs equently (weeks 3 and 4), signal intensity at sites of incipient damage inc reased and patches enlarged and coalesced. After 2 weeks of storage, the ex tent of affected tissue, averaged across all image slices, was 1.5%, increa sing to 15.9% and 21.3% after 3 and 4 weeks. The average rate at which tiss ue damage spread in individual slices was 0.81 (range: 0-3.70) cm.d(-1) bet ween weeks 2 and 3, declining to 0.32 (range: 0-1.55) cm(2).d(-1) in the fi nal week. Tissue damage induced under these conditions did not spread at th e same rate at all locations within individual fruit, nor was it preferenti ally located toward the stem or calyx ends of the fruit.