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- Author or Editor: Douglas M. Burmeister x
Development of browning induced in `Braeburn' apple (Malus ×domestica Borkh.) fruit by a damaging CO2 concentration was monitored weekly using magnetic resonance imaging (MRI) during a 4-week storage trial (0.5 °C, 2 kPa O2/7 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) cm2·d–1 between weeks 2 and 3, declining to 0.32 (range: 0–1.55) cm2·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.
In a 2-year study, induction of bitter pit-like symptoms (Mg2+ induced pits) on Northern Spy apples (Malus domestica borkh.) by infiltrating Mg2+ salt solutions into the fruits was positively correlated with bitter pit that developed during storage. Fruits at harvest were infiltrated with 0.1M MgCl2 in 0.3 M sorbitol with 0.1% Tween 20 and placed at 20°C for 10 days (d) after which the number of Mg2+ induced pits (MgIP) was determined on individual fruits. A parallel sample of fruits from each orchard was stored at 5°C in air (both years) and at 3°C in air or controlled atmosphere (CA) storage. The prediction was reliable for fruits harvested 20d and 10d before and at optimal maturity for long term storage. The endogenous (native) fruit Ca2+ concentration was inversely related to the number of pits induced by Mg2+ and to bitter pit development during storage. Pitting induced on the surface of fruits by Mg2+ treatment may thus be a reliable indicator of the potential of fruits to develop natural bitter pit.
`Braeburn' apple (Malus ×domestica Borkh.) fruit can be susceptible to the development of an internal disorder called “`Braeburn' browning disorder” (BBD). Factors associated with development of this disorder were investigated. Susceptibility to injury was greater in fruit exposed to 2 or 5 kPa CO2 than to 0 kPa CO2 during storage. Susceptibility also increased with decreasing O2 partial pressure in the range of 5 to 1 kPa in the storage atmosphere. However, fruit stored in 1 kPa O2 remained firmer than those stored at higher partial pressures, regardless of CO2 level. BBD appeared to develop during the first 2 weeks of storage, and delays in air at 0 °C prior to controlled-atmosphere (CA) storage decreased incidence and severity of the disorder. The incidence of BBD was also reduced when the time to establish CA conditions was prolonged. We recommend that `Braeburn' apples be stored under CA conditions of ≤1.0 kPa CO2 and 3.0 kPa O2. Delayed application of CA for 2 weeks after fruit enter the coldstorage may also reduce development of BBD.