To investigate different step down cooling regimes, utilised in conjunction with 1-MCP, to reduce the risk of internal browning of Cripps’ Pink apples and provide year round supply of good quality fruit.

Internal browning (IB) of ‘Cripps’ Pink’ apples is a worldwide tendency. It has been a very important internal defect in the past, costing the South African industry millions of Rands in revenue. The types of browning in this cultivar have been verified (Figures 25 a – h), and current storage regimes adapted according to the knowledge of the risk factors involved for shorter-term controlled atmosphere (CA) storage (up to 5 months). However, long-term controlled atmosphere (CA) storage (7-9 months) is still at risk of developing diffuse browning in particular. Certain step down cooling strategies in conjunction with 1-Methylcyclopropene (1-MCP) are currently being utilised in other Southern Hemisphere countries with good success for long-term storage. The objective of this study therefore was to investigate different step down cooling regimes, utilised in conjunction with 1-MCP, to reduce the risk of internal browning of ‘Cripps’ Pink’ apples and provide longer supply of good quality fruit.

‘Cripps’ Pink’ apples were sourced in the Grabouw and Ceres areas from internal browning risk orchards (5 populations/ orchards per area) and subjected to step down cooling regimes compared to no step down cooling, with or without 1-MCP, after 9 months in CA (0.5% CO₂ and 1.5% O₂) + 4 weeks regular atmosphere (RA) and a 7 day shelf life period. Misshapen fruit (Figure 25 f) were excluded at harvest.

• Fruit quality for step-cooled fruit in conjunction with 1-MCP was better maintained compared to single temperature stored fruit.
• Diffuse browning was higher in non-step cooled
• A risk of radial browning development was identified if fruit were subjected to 1-MCP and not step cooled in the 2018-19 season (Year 2). In the 2019-20 season (Year 3) both 1-MCP and non-1-MCP treated fruit stored at single temperature without step cooling had a higher incidence of radial browning after CA storage compared to step cooled fruit, but in some evaluation dates the same trend was seen as in Year 2.

In Year 2, step down cooling starting from 3 °C proved to be more favourable than starting from 4 °C, delivering the best (least defects) and most consistent results. In Year 3 when ‘Cripps’ Pink’ apples from both areas were able to be harvested well within the 30 – 40% starch conversion range, step down cooling starting from 3 °C or 4 °C proved to yield similar results with regards to internal browning development. In some cases starting step cooling from 4 °C yielded less radial browning, without significantly adversely affecting other quality parameters (except for few CO₂ blotches, that could have been non-related), but further investigation around the specific step cooling protocol, the delay duration before onset of CA and total storage duration to be followed commercially, is required.

• Contrary to mostly inconclusive results found in the low risk 2017-2018 season (Year 1), the 2018-2019 season (Year 2) was a high-risk season for internal browning development and clear treatment differences were exhibited. A risk for diffuse and radial browning development was identified in not first step down cooling ‘Cripps’ Pink’ apples in conjunction with the use of 1-MCP and a potential area and/ or maturity related risk was exhibited (diffuse browning affected by post-optimum harvest and radial browning more affected by pre-optimum harvest). This substantiates previous studies’ results that affect best practice handling protocols. From industry feedback, the 2019-2020 season (Year 3) was another high risk year, but harvest maturities for the two areas (so called “extremes” climate wise) coincided and it was possible to harvest both areas within the optimum picking window (30-40% starch conversion) one day apart. This resulted in further insights on how adhering to harvest maturity could enable successful marketing of good quality ‘Cripps’ Pink’ apples in addition to certain adjusted storage protocols and avoiding single temperature regimes.
• In 2021, internal browning incidence will be further evaluated after dynamic controlled atmospheres in long term storage and will include pre-harvest factors such as canopy position and pre-harvest
• Further investigation around the specific step cooling protocol, the delay duration before onset of CA and total storage duration to be followed commercially, is required (New project application 2022_ExperiCo).