Introduction
Internal browning (IB) of ‘Cripps’ Pink’ apples is a worldwide issue, costing the South African industry millions of Rands in revenue.
Types of Internal Browning (IB) Identified:
- Radial
- Diffuse
- Combination
- CO₂ cavities
- Misshapen fruit
Visual Examples
- Radial browning
- Diffuse browning
- Combination browning
- CO₂ cavities (core and flesh)
- Misshapen fruit
Rationale
- IB is a global tendency in ‘Cripps’ Pink’ apples.
- Has cost the South African industry millions in revenue.
- Types of IB: Radial, Diffuse, Combination, CO₂ cavities, Misshapen fruit browning.
- Storage regimes have been adapted: fruit stored above 0°C and for shorter-term CA storage (max 4–5 months).
- However, longer-term CA storage (7–9 months) still poses a risk for IB.
Risk Factors for IB
Pre-harvest factors:
- Orchard factors
- Seasonal climatic variables
- Harvest maturity
Postharvest factors:
- Cooling rate
- 1-MCP application
- CA/DCA conditions
- Storage temperature
- Storage duration
A Possible Solution
- Step cooling has proven to reduce stress on fruit.
- This trial tested a successful step cooling regime, in conjunction with 1-MCP, to reduce IB potential.
Materials and Methods
- Areas: Ceres and Grabouw
- Populations: 10 (5 per area)
- Harvest maturity: 30–40% starch breakdown (SB)
- 1-MCP: Applied within 7 days
- Cooling regimes: 5 treatments
Treatments
| Treatment | April (Harvest) | 1-MCP (7 days) | 30 days | 30 days | 30 days | Sept | Jan (Open CA) |
|---|---|---|---|---|---|---|---|
| T1 (US) | 4°C | 3°C | 2°C | 1°C | 1°C | ||
| T2 (US) | 3°C | 2°C | 1°C | 1°C | 1°C | ||
| T3 (Comm.) | 14d 2°C | 14d 1°C | 0.5°C | 1°C | 1°C | ||
| T4 (US) | 1°C | 1°C | 1°C | 1°C | 1°C | ||
| T5 (US) | 1°C | 1°C | 1°C | 1°C | 1°C |
Examinations
- Full maturity at time of harvest
- After 9 months CA (1.5% O₂; 0.5% CO₂)
- After 4 weeks RA at -0.5°C
- After 7 days shelf life at 20°C
What Has Been Learnt?
- Harvest at optimum maturity
- Apply 1-MCP
- Step cool
Maturity at Harvest
- 2017–18 (Year 1): Low risk commercial browning year
- 2018–19 (Year 2): High risk commercial browning year
- 2019–20 (Year 3): High risk commercial browning year
Starch (2017–2019; Years 1–3)
- Low risk: Low IB
- High risk: High IB
Firmness at Harvest and After Storage
- Firmness measured at harvest, after CA, after RA, and after shelf life for each year.
Browning After Storage
- Radial and diffuse browning measured after CA, RA, and shelf life for each year.
Key Results
- Storing for up to 9 months CA is not recommended (IB risk in high-risk years).
- These conditions were followed for trial purposes only to identify possible risk protocols not to be followed commercially.
- Area differences possibly due to harvest maturity.
Yearly Risk Summary
- 2017–2018 (Year 1): Low risk year
- 2018–2019 (Year 2): High risk year – clear treatment differences
- Risk for IB (radial and diffuse) and fruit quality if not step cooled (starting at 3°C)
- Risk of radial browning if not step cooled and subjected to 1-MCP
- Radial browning seems linked to less mature fruit
- Diffuse browning related to overmaturity and low storage temperature, substantiating previous results
- 2019–2020 (Year 3): High risk year – low IB incidence (HMI: 30–40%)
Conclusion
- Step cooling and careful management of storage regimes are critical to minimize IB and maintain fruit quality in ‘Cripps’ Pink’ apples.
- Long-term CA storage (7–9 months) increases risk, especially in high-risk years or with improper protocols.
Thank you!
Heleen Tayler, ExperiCo (Agri-Research Solutions)
heleen@experico.co.za | +27 21 887 1134