3.2.2. Background Color

In the 2015 season, L\* values fluctuated across all treatments, from day 0 to 10 months of storage. The pattern of change for L\* was not clear. However, between 2 and 8 months, L\* values were mostly higher than values at day 0 (Figure 2a). In the period between 2 and 10 months, apples stored using RA recorded lesser negative a\* values (less green) compared with RLOS (ULO and CA) and DCA-CF treatments (Figure 2b).

As observed in Figure 2c between 2 and 4 months, apples stored using DCA-CF recorded higher b\* values (more yellow) than RLOS (ULO and CA) and RA treatments. However, from 4 to 10 months, the pattern of change of b\* fluctuated, with apples stored using RA recording the lowest b\* values (6, 8, and 10 months). There was a marked decrease in h◦ of 'Granny Smith' apples from 6 to 10 months of storage in RA (Figure 2d). However, RLOS (ULO and CA) and DCA-CF maintained h◦ and influence background color retention at 0 and 7 d shelf life.

In the 2016 season, the pattern of change in L\* was not clear (Figure 3a). However, across all storage treatments, L\* values recorded at day 0 were lower than other storage periods. The L\* values fluctuated, and at certain points (2, 4, and 8 months), apples stored using RLOS + ULO recorded the highest L\* values compared with RLOS + CA, DCA-CF, and RA. Similar to the 2015 season, apples stored using RA mostly recorded less negative a\* values (less green) compared with RLOS (ULO and CA) and DCA-CF (Figure 3b). The values for color attribute b\* mostly fluctuated during storage, and the differences between storage treatments were mostly not significant (Figure 3c). A similar trend was observed with smaller differences in h◦ between low oxygen technologies (RLOS + ULO, RLOS + CA, and DCA-CF) and RA storage (Figure 3d). Overall, RLOS (ULO and CA) and DCA-CF appeared to reduce loss of h◦, especially in the 2015 season.

#### 3.2.3. Total Soluble Solids and Titratable Acidity

In the first harvest season (2015), the results showed no statistical differences in TSS content between RLOS (ULO and CA) and DCA-CF treated apples (Figure 4a). Across all treatments, TSS content fluctuated during storage. However, in the second harvest season (2016) (Figure 4b), the results showed that low oxygen treatments retained significantly higher TSS content than RA treated fruit. Nevertheless, based on the two seasons, RLOS (ULO and CA) and DCA-CF treatments maintained TSS content significantly higher with RA during long term storage.

In the 2015 harvest season, TA measured from RLOS + CA stored apples decreased from 4 to 10 months storage (Figure 5a). There was a general decrease in TA content during storage of RA treated fruit, with significant changes occurring between 4 to 10 months. The TA content was lower in RA treated fruit than in DCA-CF and RLOS (ULO and CA) treatments, especially from 6 to 10 months. Moreover, there was a decrease in TA from 0 to 7 d shelf life for RLOS + ULO, RA, and DCA-CF treated fruit. As with the 2015 harvest season, RA treated fruit generally had lower TA content than fruit subjected to RLOS (ULO and CA) and DCA-CF treatments throughout storage (Figure 5b). The rate of decrease in TA was higher for RA stored apples compared RLOS (ULO and CA) and DCA-CF treated apples.

**Figure 2.** Background color (**a**) lightness (L\*), (**b**) redness/greenness (a\*), (**c**) yellowness/blueness (b\*) and (**d**) hue angle (h◦) of 'Granny Smith' apples harvested in the 2015 season at commercial maturity and stored for up to 10 months at 0 ◦C in various storage conditions, evaluated every two months followed by a 6 week simulated shipment and handling period, and at 7 days on the shelf (20 ◦C and 65% RH). Vertical bars represent the standard error (SE) of mean values of 3 replicates (1 replicate = 10 fruit). LSD0.05 represents least significant difference (*p* < 0.05). For storage duration, mon—months; w—weeks; and d—days. RLOS—repeated low oxygen stress; ULO—ultra-low oxygen; CA—controlled atmosphere; DCA-CF—dynamic controlled atmosphere-chlorophyll fluorescence; RA—regular atmosphere.

**Figure 3.** Background color (**a**) lightness (L\*), (**b**) redness/greenness (a\*), (**c**) yellowness/blueness (b\*) and (**d**) hue angle (h◦) of 'Granny Smith' apples harvested in the 2016 season at commercial maturity and stored for up to 10 months at 0 ◦C in various storage conditions, evaluated every two months followed by a 6 week simulated shipment and handling period, and at 7 days on the shelf (20 ◦C and 65% RH). Vertical bars represent the standard error (SE) of mean values of 3 replicates (1 replicate = 10 fruit). LSD0.05 represents least significant difference (*p* < 0.05). For storage duration, mon—months; w—weeks; and d—days. RLOS—repeated low oxygen stress; ULO—ultra-low oxygen; CA—controlled atmosphere; DCA-CF—dynamic controlled atmosphere-chlorophyll fluorescence; RA—regular atmosphere.

**Figure 4.** Total soluble solids (◦Brix) of 'Granny Smith' apples harvested in the 2015 (**a**) and 2016 (**b**) seasons at commercial maturity and stored for up to 10 months at 0 ◦C in various storage conditions, evaluated every two months followed by a 6 week simulated shipment and handling period, and at 7 days on the shelf (20 ◦C and 65% RH). Vertical bars represent the standard error (SE) of mean values of 3 replicates (1 replicate = 10 fruit). LSD0.05 represents least significant difference (*p* < 0.05). For storage duration, mon—months; w—weeks; and d—days. RLOS—repeated low oxygen stress; ULO—ultra-low oxygen; CA—controlled atmosphere; DCA-CF—dynamic controlled atmosphere-chlorophyll fluorescence; RA—regular atmosphere.

**Figure 5.** Titratable acidity (g/100 g MA) of 'Granny Smith' apples harvested in the 2015 (**a**) and 2016 (**b**) seasons at commercial maturity and stored for up to 10 months at 0 ◦C in various storage conditions, evaluated every two months followed by a 6 week simulated shipment and handling period, and at 7 days on the shelf (20 ◦C and 65% RH). Vertical bars represent the standard error (SE) of mean values of 3 replicates (1 replicate = 10 fruit). LSD0.05 represents least significant difference (*p* < 0.05). For storage duration, mon—months; w—weeks; and d—days. RLOS—repeated low oxygen stress; ULO—ultra-low oxygen; CA—controlled atmosphere; DCA-CF—dynamic controlled atmosphere-chlorophyll fluorescence; RA—regular atmosphere.

#### *3.3. Headspace Volatile Analysis*

Changes in MHO and α-farnesene contents during storage for both harvest seasons (2015 and 2016) are presented in Figures 6 and 7, respectively. In the first season (2015), MHO accumulation was markedly higher in RA treated peels from 4 to 6 months (7 d shelf life) and from 8 to 10 months (0 and 7 d shelf life), compared to RLOS (ULO and CA) and DCA-CF sampled peels (Figure 6a). Similarly, in the second season (2016), the

accumulation of MHO was significantly higher after 6 and 8 months (7 d shelf life), and 10 months (0 d shelf life) for RA treated peels compared to RLOS (ULO and CA) and DCA-CF stored peels (Figure 6b). For both seasons (2015 and 2016), α-farnesene content was significantly higher in RA treated peels after 6 months compared to RLOS (ULO and CA) and DCA-CF treatments (Figure 7a,b). During storage, α-farnesene content was generally stable in peels sampled from RLOS (ULO and CA) and DCA-CF stored apple. On the contrary, in RA treated peels, α-farnesene steadily increased, reaching its peak at around 6 months of storage and subsequently declining.

**Figure 6.** Accumulation of MHO (Log (%)) of 'Granny Smith' apples harvested in the 2015 (**a**) and 2016 (**b**) seasons at commercial maturity and stored for up to 10 months at 0 ◦C in various storage conditions, evaluated every two months followed by a 6 week simulated shipment and handling period, and at 7 days on the shelf (20 ◦C and 65% RH). Vertical bars represent the standard error (SE) of mean values of 3 replicates (1 replicate = 10 fruit). LSD0.05 represents least significant difference (*p* < 0.05). For storage duration, mon—months; w—weeks; and d—days. RLOS—repeated low oxygen stress; ULO—ultra-low oxygen; CA—controlled atmosphere; DCA-CF—dynamic controlled atmosphere-chlorophyll fluorescence; RA—regular atmosphere.

**Figure 7.** Alpha-farnesene (Log% peak area) of 'Granny Smith' apples harvested in the 2015 (**a**) and 2016 (**b**) seasons at commercial maturity and stored for up to 10 months at 0 ◦C in various storage conditions, evaluated every two months followed by a 6 week simulated shipment and handling period, and at 7 days on the shelf (20 ◦C and 65% RH). Vertical bars represent the standard error (SE) of mean values of 3 replicates (1 replicate = 10 fruit). LSD0.05 represents least significant difference (*p* < 0.05). LSD0.05 represent least significant difference (*p* < 0.05). For storage duration, mon—months; w—week; and d—days. RLOS—repeated low oxygen stress; ULO—ultra-low oxygen; CA—controlled atmosphere; DCA-CF—dynamic controlled atmosphere-chlorophyll fluorescence; RA—regular atmosphere.
