Delayed CA and oxygen at 1 kPa or less control superficial scald without CO2 injury on Bramley’s Seedling apples

Abstract

Controlled atmosphere (CA) storage experiments were carried out on Bramley’s Seedling (Bramley) apples (Malus domestica Borkh.) over 2 years to determine the extent to which CO2 injury could be ameliorated by delayed establishment of a storage atmosphere that deters scald, and the potential for reducing store O2 concentration below 1 kPa to compensate for loss of scald control through delayed atmosphere establishment. Bramley apples from 15 commercial orchards did not develop external or internal CO2 injury when the sealing of CA containers was delayed by 10 days from loading (5 days from the completion of cooling to 4°C). CA conditions of 5 kPa CO2 and 1 kPa O2 (5/1) were established subsequently by fruit respiration. Longer delays were required where conditions were established by flushing with N2 and CO2 immediately after sealing. Some internal injury (brownheart) occurred after establishment of CA conditions by flushing, despite a 15 day delay. Scald was controlled less effectively when establishment of 5/1 conditions was delayed, particularly if these were achieved by fruit respiration rather than by flushing. A progressive reduction in scald was achieved by maintaining O2 concentrations at 0.8, 0.6 or 0.4 kPa, in the presence of 5 kPa CO2. Although products of anaerobic respiration increased progressively at lower oxygen concentrations, these remained below suggested olfactory thresholds. A strategy was devised for CA establishment and storage conditions that prevent CO2 injury and extend the scald-free period of apples not treated with a chemical antioxidant prior to storage.