Minimum exposure period for dynamic controlled atmospheres to control superficial scald in 'Granny Smith' apples for long distance supply chains

This study was conducted to investigate the potential of dynamic controlled atmospheres (DCA) to control superficial scald in pre-optimally and optimally harvested 'Granny Smith' apples over two growing seasons. The critical minimum period for DCA to control superficial scald was also investigated. Fruit were stored in DCA at 0 °C for 5 d up to 20 w followed by 6 or 10 w simulated handling temperature (−0.5 °C) for long distant supply chains plus 7 d at 20 °C. The scald potential for each storage duration in each season was assessed by storing fruit in air as the control treatment. To determine critical minimum storage period, simulated shipping of fruit in air for extended period of 10 w was used. Superficial scald incidence and fruit quality parameters such as total soluble solids (TSS), titratable acidity (TA), fruit firmness and ground colour were measured. The evolution of metabolites (α-farnesene, 6-methyl-5-hepten-2-one (MHO) and ethylene) associated with scald development were also monitored. The results showed that DCA controlled superficial scald in pre-optimally and optimally harvested fruit in both growing seasons. Results on the minimum exposure period were highly inconsistent over the two season, however, it was found that exposing DCA treated fruit to 10 w shipment period increases the risk of superficial scald development. All DCA treated fruit, regardless of the exposure period, can withstand only 6 w shipment period. For all the storage regimes, DCA stored fruit appeared to have a higher ground colour and fruit firmness compared to air stored fruit. All DCA stored fruit had lower concentrations of ethylene, α-farnesene and MHO. The Pearson's correlation showed a strong relationship among scald associated metabolites. Correlation coefficient for α-farnesene and MHO of fruit stored in air and DCA were 0.831 and 0.822, respectively, while those for scald incidence and MHO were 0.863 and 0.365 in air and DCA, respectively.