Control of the critical oxygen level during dynamic CA storage of apples

The concept of dynamic CA storage (DCA) involves the reduction of the oxygen level in the storage atmosphere to near the lowest level tolerated by the fruit, the so-called anaerobic compensation point. Fruit quality loss during DCA storage is presumed to be slowed down compared to normal ULO storage. Storage conditions below the critical oxygen level will cause anaerobic conditions followed by severe quality losses in stored fruit. Two methods based on RQ and fluorescence signal F-α monitoring have been tested to detect the critical oxygen concentration (ACP) during dynamic CA-storage (DCA) of several apple varieties. Both methods yielded identical oxygen values for ACP. ACPs found were at concentrations as low as 0.2 – 0.4%, depending on the apple variety. After the critical oxygen limit was reached, the oxygen concentration was increased by about 0.1 – 0.3% above the critical limit. In this way, fruits were held for 200 days at oxygen levels of 0.3% to 0.6% without causing physiological disorders. Fruit firmness values of DCA stored apples were in general significantly higher than those of ULO-stored control fruit after storage for about 200 days.