Monitoring of extremely low oxygen control atmosphere storage of ‘Greenstar’ apples using chlorophyll fluorescence

• Hypoxic stress in Greenstar apples was monitored with chlorophyll fluorescence sensor.
• Fruit stored at 0.4% O2 retained color better than control fruits stored at 2% O2.
• Other quality attributes of fruit stored at 0.4% O2 were not significantly different.
• All fruit were free of disorder irrespective of the investigated storage conditions.

A chlorophyll fluorescence-based technology to monitor low-oxygen stress during controlled atmosphere (CA) storage was tested on apples (Malus domestica Borkh. cv. Greenstar). A static CA regime of 2% oxygen was established in a CA unit for the control fruit. In two other CA units apple fruit were exposed to extremely low oxygen conditions while monitoring the fluorescence signal. The latter spiked when the oxygen level was reduced below 0.2%. The oxygen level was subsequently set to 0.4% in one CA unit and 0.7% in the other. In all CA units the temperature and CO2 levels were maintained at 1.2 ± 0.2 °C and 3%, respectively. Instrumental measurements were used to analyze quality attributes of apples at harvest and after 1, 4.5, 7 and 10 months of storage plus 0 day and 7 days of shelf life. Sensory quality was evaluated after 4.5 and 10 months of storage. After 10 months of storage, apples stored in extremely low oxygen controlled atmosphere storage had a better color retention than control fruits. The apple firmness, SSC and acidity were not affected by the storage condition. Sensory evaluation tests indicated no significant difference between the two storage conditions. Apples removed after 10 months of storage plus 7 days of shelf life were completely free of any disorder in both storage conditions. By using chlorophyll fluorescence as an effective non-destructive indicator to monitor the response of ‘Greenstar’ apples to extremely low oxygen conditions, it is thus possible to optimize the storage atmosphere for the specific product in a given year with maximum quality retention.