POSTHARVEST INTERNAL BROWNING DURING CA STORAGE OF 'SANTANA' APPLES - REASONS AND POSSIBILITIES TO REDUCE THE DISORDER

‘Santana’ is a scab resistant, early ripening apple cultivar commercially important for organic production in the Lake Constance region (southern Germany). However, ‘Santana’ is highly sensitive to an internal flesh browning disorder during controlled atmosphere storage (CA). We investigated some possible reasons for the incidence of this physiological disorder and looked for methods to prevent it. In four experimental years, organically grown ‘Santana’ apples were harvested from two different orchards in the Lake Constance area. During a 5-month storage period the influence of the following factors on disorder occurrence were investigated: preharvest calcium applications, harvest date, time of CA establishment, storage temperature and CA composition. Weekly calcium applications (8 to 10 sprays with calcium chloride beginning after June drop until harvest) reduced internal browning during storage. A 3-week postharvest delay in regular air (RA) before CA establishment, as successfully used to reduce internal flesh browning in other sensitive apple cultivars like ‘Braeburn’, failed and fruit from delayed CA storage showed increased browning disorders. One key factor to control flesh browning was the level of CO₂ partial pressure (0.7 to 1.0 kPa). With increased CO₂ partial pressures (>3.0 kPa) a significant higher incidence of internal browning was observed. O₂ levels between 1.0 and 1.5 kPa seem to be suitable, as lower O₂ levels (<1.0 kPa) potentially increase the risk for internal browning and higher O₂ levels (>2.0 kPa) the risk for scald. In addition, apples from later harvest dates were much more susceptible to browning when compared to earlier picked fruit. ‘Santana’ was not sensitive to low storage temperatures.