‘Quo Vadis’ – Long Term CA Storage Regimes of Cripps’ Pink Apples and Fruit Quality

Authors: H Tayler, D Viljoen, E Crouch, T Kholoane

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) Verified:

• Radial
• Diffuse
• Combination
• CO₂/cavities
• Misshapen fruit

Visual Examples

• Radial browning
• Diffuse browning
• Combination browning
• CO₂ cavities (core and general)
• Misshapen fruit

Rationale

• Internal browning (IB) of Cripps’ Pink apples is a global tendency.
• Has cost the South African industry millions in revenue.
• Types of IB in this cultivar: Radial, Diffuse, Combination, CO₂/cavities, and 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

IB potential is determined by:

Pre-harvest factors:

• Growing region
• Orchard factors
• Seasonal climatic variables
• Harvest maturity

Postharvest factors:

• Cooling rate
• 1-MCP treatment
• CA conditions
• Storage temperature
• Storage time

Step Cooling

• Step cooling has proven to reduce stress on fruit.
• This trial tested a successful step cooling regime, in conjunction with 1-MCP (SmartFreshSM), to reduce IB potential.

Materials and Methods

• Areas: Ceres and Grabouw
• Populations: 10 (5 per area)
• Harvest maturity: Optimum (30–40% starch breakdown)
• 1-MCP (SmartFreshSM): Within 7 days
• Cooling regimes: 5 treatments

Treatments

Examinations

• Full maturity at time of harvest
• After 9 months CA
• After 4 weeks RA at -0.5°C
• After 7 days shelf life at 20.0°C

Note: Data analyzed as two-way factorial: Farm × Treatment

Maturity at Harvest (2018–19 Season; Year 2)

Factors Measured

• Firmness (kg)
• Background Colour (Chart index)
• Blush Colour Intensity (Pl 16)
• Blush Colour (%)
• TSS (%)
• TA (%)
• Starch (%)
• Internal Ethylene (µL/L)
• Internal CO₂ (%)
• Internal O₂ (%)

Example Data (Ceres & Grabouw/Elgin)

Full table omitted for brevity.

Results: Key Parameters After Storage

After CA

• Firmness, background colour, TSS, TA, internal ethylene, internal CO₂, and browning types measured.

After RA

• Similar parameters measured, including light diffuse and combination browning.

After Shelf

• Firmness, TSS, TA, internal ethylene, internal CO₂, diffuse and combination browning.

Example: Other Parameters – After CA

Statistical Analysis

• Significant effects found for farm, treatment, and their interaction on various parameters (see tables for Pr>F values).

Key Results

• Storing for up to 9 months CA is not recommended at this stage (high superficial scald & IB in high-risk years).
• These conditions were followed for trial purposes only to identify possible risk protocols not to be followed commercially.
• Area differences were possibly due to harvest maturity differences.

Yearly Risk Summary

• 2017–2018 (Year 1): Low risk
• 2018–2019 (Year 2): High risk – 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
  • Risk for radial browning seems linked to less mature fruit
  • Diffuse browning related to over-maturity and low storage temperature, substantiating previous results
• 2019–2020 (Year 3): Currently in storage

Conclusions

• 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!