Internal browning of ‘Cripps Pink’ apples – DCA-CF and long-term storage with best practice protocol.

 Long-term CA storage (6 to 9 months) poses a risk of internal browning (IB) in ‘Cripps Pink’ apples. Dynamic Controlled Atmosphere-Chlorophyll Fluorescence (DCA-CF) alongside the recommended best practice protocol (optimum maturity, 1-MCP application, and step-down cooling; Tayler and Crouch, Hortgro report, August 2019) were evaluated to mitigate the IB risk.

In 2021 and 2022 fruit of optimum maturity were harvested in the Langkloof (2021) and Ceres, however the Langkloof fruit arrived at the storage facility at post-optimum maturity in both seasons. In 2023 fruit of optimum and post-optimum maturity were harvested from the same farm in Grabouw to enable the statistical comparison of different fruit maturities as well as the storage technique on fruit quality. Fruit was treated with 1-MCP and stored under DCA-CF (LOL ≈ 0.4 kPa O₂ + <0.5 kPa CO₂) or CA (1.5 kPa  O₂ + 0.5 kPa  CO₂) for 30 d at 3 °C + 30 d at 2 °C + remainder of storage duration at 1 °C. Fruit was evaluated after 9 months storage, 6 weeks in RA at 1 °C and 7 d shelf-life at 20 °C.

• Unrefrigerated transport of fruit over long distances after harvest resulted in significant increases in starch breakdown in 2021. It is, therefore, important to determine fruit maturity before cold storage begins, as the initial maturity will impact the storage outcomes.
• DCA-CF storage did not mitigate IB development better than CA storage, especially when fruit were over mature, but gave a better control over superficial and peduncular scald.
• DCA-CF retained fruit firmness, TSS, and TA better in optimum and post-optimum maturity fruit than CA.
• Diffuse browning (DB) and combination browning (CB) were associated with larger and over mature fruit.
• Radial browning (RB) was not associated with any fruit quality parameters measured in this study. The drivers for RB may possibly be pre-harvest temperature and/or orchard factors.

• Fruit maturity before the commencement of storage is the main driver for IB in ‘Cripps Pink’ apples. Therefore, it is not recommended for post-optimum fruit to be stored under low-oxygen treatments.
• DB was found to be linked to fruit size rather than low-oxygen storage treatment. Therefore, future studies should investigate what threshold fruit size predisposes ‘Cripps Pink’ to DB development.
• RB was not associated with any variable measured in this study.
• The results showed that DCA-CF storage did not provide a greater benefit than CA storage in preventing IB in ‘Cripps’ Pink’ apples, especially in post-optimum stored fruit.
• Superficial and peduncular scald were notably reduced in DCA-CF storage and had higher incidence in post-optimum fruit.
• DCA-CF retained TSS, TA and firmness better in optimum and post-optimum maturity fruit after simulated shipping compared to CA storage. However, the effect was lost during simulated shelf-life.

The transportation and handling of fruit after harvest, before the start of cold storage, led to a significant increase in starch breakdown in some seasons. Therefore, it is important to determine the maturity of ‘Cripps Pink’ apples before cold storage begins to make informed decisions about storage duration and the use of low-oxygen storage.

DCA-CF is advised for ‘Cripps Pink’ apples at optimum maturity as it reduces superficial and peduncular scald and gives better retention of TSS, TA and fruit firmness until after the shipping period. However, it does not give better control of IB compared to CA.