4.2.2. Background Color

The pattern of change for color attribute a\* in the 2015 and 2016 seasons suggested that RLOS (ULO and CA) and DCA-CF treatments minimized the decrease in the green color of 'Granny Smith' apples. The results corroborate with Zanella [35], who observed minimal change in the green color of 'Granny Smith' apples stored using low oxygen (0.4 kPa O2) and CA (1.5 kPa O2 and 1.3 kPa CO2) compared with RA (21 kPa O2 and 0.03 kPa CO2). Likewise, studies by Mditshwa et al. [2] showed that repeated application of DCA-CF (0.3–0.5% O2 and 1% CO2) maintained the green color of 'Granny Smith' apples during cold storage (0 ◦C and 95% RH).

Overall, RLOS (ULO and CA) and DCA-CF reduced h◦ loss of 'Granny Smith' apples compared to RA, especially in the first harvest season (2015 season) when the risk of scald development was low. This indicates that low oxygen technologies resulted in fresher green color, while lower hue values denoted a more yellowish background color of apples subjected to RA storage. Similar results were reported for 'Granny Smith' apples and 'd'Anjou' pears subjected to low oxygen technologies such as ULO and DCA-CF during cold storage [13,19,35], which limited the decrease in h◦ by possibly reducing chlorophyll breakdown due to leakage of organic acid from the vacuole, oxidative stress, and chlorophyllases [24].

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

Overall, RLOS (ULO and CA) and DCA-CF maintained TSS content significantly higher than RA during long term storage. The results were in accordance with Rebeaud and Gasser [40], who reported higher TSS content in DCA-CF stored 'Golden Delicious' apples compared to RA stored fruit after 16 and 36 w of cold storage. Titratable acidity content of 'Granny Smith' apples usually decreases as storage duration is extended [43]. The use of fruit organic acids in respiration during storage has been suggested as the cause for decreases in TA content [44–46]. The RLOS (ULO and CA) and DCA-CF treatments reduced the decline in TA as storage duration was extended whilst there was a general decrease in TA content during storage of RA treated fruit. These results agree with Mditshwa et al. [9], who reported that 'Granny Smith' apples stored in repeated DCA-CF had higher TA levels compared to RA stored fruit. Similarly, Lafer [47] reported that DCA-CF storage maintained firmness and TA content at higher levels for 'Uta' pears compared to standard CA.
