*2.1. Fruit Supply, Treatments and Storage*

'Granny Smith' apples were harvested at 172 days after full bloom (DAFB) with an average starch breakdown = 36.3% and firmness = 79 N from Grabouw (34◦12 12 S, 19◦02 35 E), Western Cape, South Africa. Fruit were transported to the research laboratory at the Agricultural Research Council (ARC), Stellenbosch, South Africa. 'Granny Smith' apples were sorted for external damages, packaged in crates (90–120 fruit per crate), and stored at 0 ◦C. Each treatment had 3 replications (1 crate=1replication = 90–120 fruit). Subsequently, 'Granny Smith' apples were subjected to the following repeated low oxygen stress (RLOS) treatments: (1) low oxygen stress at 0.5% O2 for 10 d followed by ultra-low oxygen (ULO) (0.9% O2 and 0.8% CO2) for 21 d and low oxygen stress at 0.5% for 7 d, (2) low oxygen stress at 0.5% O2 for 10 d followed by controlled atmosphere (CA) (1.5% O2 and 1% CO2) for 21 d, and low oxygen stress at 0.5% O2 for 7 d.

Existing CA cold rooms were installed with the HarvestWatch® (SAtlantic Inc., Halifax, NS, Canada) chlorophyll fluorescence non-destructive monitoring system. The interactive response monitor sensor (FIRM) was used to detect the low oxygen limit (LOL) of the fruit and monitor the physiological response of the fruit to low oxygen levels hourly. Following the storage protocol reported by Mditshwa et al. [2], 'Granny Smith' apples were loaded into cold rooms, and a core temperature of −0.5 ◦C was achieved within 48–96 h after harvest. Low oxygen limit of the fruit was detected within 48 h after harvest, using compressed air, carbon dioxide, and nitrogen from a membrane generator (Isosep, Isolcell, Italy). The LOL was set at 0.3% O2 for both harvest seasons (2015 and 2016), after which it was set to 0.6% O2 for the entire storage period. In this study, gas composition needed to be adjusted to prevent a shift to the anaerobic respiration of fruit, so the storage room chamber was analyzed at 90 min intervals. Fruit were also stored in RA at 0 ◦C (≈21% O2 and 90–95% RH). The study was repeated over two consecutive seasons (2015 and 2016). In summary, 'Granny Smith' apples were stored using the following treatments (1–4):


#### *2.2. Assessment of Quality and Analysis*
