Presenter: Anél Botes
Event: CA Meeting – 6 November 2018
1. Introduction
Non-Chemical Technologies Available to the South African Pear Industry
- DCA-CF: Dynamic Controlled Atmosphere – Chlorophyll Fluorescence
- DCA-CF + 1-MCP: DCA-CF with 1-MCP (before packaging)
- ILOS + CA: Initial Low Oxygen Stress plus Controlled Atmosphere
2. RLOS Protocol Overview
- RLOS: Repeated cycles of low oxygen stress with ethanol monitoring
- Protocol Steps:
- LOS (Low Oxygen Stress) followed by ULO (Ultra Low Oxygen) phase
- Ethanol measured after each stress period
- Stress applied every 21 days
Recommended Storage Atmospheres for Apple and Pear Cultivars
| Cultivar |
O₂ (%) |
CO₂ (%) |
| Fuji |
0.9–1.1 |
0.7–0.9 |
| Red Delicious |
0.5–0.7 |
0.8–0.9 |
| Granny |
0.5–0.7 |
0.8–0.9 |
| Gala |
0.6–0.8 |
0.9–1.0 |
| Pink Lady/Modi’ |
0.5–0.7 |
0.6–0.7 |
| Morgen/R. Beauty |
0.5–0.6 |
0.8–0.9 |
| Conf/Abate |
0.6–0.8 |
0.5–0.7 |
| PT (Packham’s Triumph) |
0.5–0.7 |
0.4–0.7 |
- Stress periods are applied according to the RLOS protocol.
- FCE: Swinglos protocol
3. Maximum Ethanol Levels Suggested During Stress Periods
| Cultivar |
Ethanol (mg/L juice) |
| Braeburn |
200–250 |
| Fuji |
70–100 |
| Gala |
50–70 |
| Golden Delicious |
70–100 |
| Granny Smith |
70–100 |
| Jonagold |
50–70 |
| Morgenduft |
70–100 |
| Pink Lady |
50–70 |
| Red Delicious |
300–400 |
| Packham’s Triumph |
100–150 |
4. RLOS Protocol for ‘Packham’s Triumph’ (PT)
- Repeated low oxygen stress (RLOS) can prevent superficial scald on PT during long-term storage (10 months).
- In some seasons, alcohol build-up during stress periods exceeds the prescribed maximum (100–150 ppm), leading to off-tastes.
- Aim: Optimize the RLOS protocol to control superficial scald on PT.
Experimental Details
- Optimum harvested PT from Grabouw (2017)
- Treatments:
- RLOS + ULO (0.9% O₂ + 0.8% CO₂)
- RLOS + CA (1.5% O₂ + 2.5% CO₂)
- RA (Regular Atmosphere)
- Storage temperature: -0.5°C
- Storage time:
- 2 months (min stress period: 1, max: 2)
- 4 months (min: 1, max: 4)
- 6 months (min: 1, max: 6)
- 8 months (min: 1, max: 8)
- 10 months (min: 1, max: 9)
- Post-storage: 6-week shipping and handling period plus 7 days at 20°C
Measurements
- Alcohol concentration (ppm): Measured with an alcoholmeter after stress periods
- Superficial scald development: Assessed after shelf-life
- Firmness: Measured after shelf-life
5. Results Overview
RLOS + ULO
- Stress periods: 1, 3, 5, 7, 9
RLOS + CA
- Similar stress period structure
6. Key Findings
- One stress period of 10 days (0.5–0.6% O₂) was effective to prevent superficial scald over long-term storage (10 months).
- High alcohol concentrations after RLOS + ULO did not result in off-tastes.
- RLOS is a viable alternative if no DCA-CF or DCA-RQ facilities are available.
7. Acknowledgements
- Funders: ARC, HortgroScience
- Technical Assistance: Howard, Viole, and Vanessa
