Presenter: Anél Botes
Event: CA Meeting – 6 November 2018
Introduction
- DPA (Diphenylamine) is an antioxidant that suppresses superficial scald and reduces internal browning (IB).
- DPA prevents the development of CO₂ injury during storage of ‘Fuji’ (Argenta et al., 2002) and ‘Honeycrisp’ apples (Cantreras, 2014).
- Fruit treated with 1-MCP and stored in CA, without DPA, developed internal browning and cavities (Mattheis and Rudell, 2008).
- Since 2015, there has been a higher incidence of IB on South African ‘Fuji’ apples, possibly linked to the discontinuation of DPA use.
Aim
- To determine if other quality benefits can be attributed to DPA application.
- Results may indicate a need to re-evaluate the current recommended gas regimes for South African pome fruit.
Materials and Methods
- Optimum harvested ‘Cripps Pink’ (2017)
- Production areas: Grabouw and Ceres
- Three sites from each production area
Treatments
- DPA + RA (Regular Atmosphere)
- DPA + CA (Controlled Atmosphere, recommended: 1.5% O₂ + 0.5% CO₂)
- DPA + HCA (High CO₂ Atmosphere: 1.5% O₂ + 2.5% CO₂)
- CA (1.5% O₂ + 0.5% CO₂)
- RA
- Storage temperature: -0.5°C
- Fruit quality evaluations: After 3, 6, and 9 months storage (+ 6 weeks RA + 7 and 14 day shelf-life)
Results
Maturity Index at Harvest
Grabouw
| Parameter |
Site 1 |
Site 2 |
Site 3 |
| Skin background colour (1–5) |
2.94 ± 0.15 |
2.86 ± 0.02 |
2.73 ± 0.09 |
| Firmness (kg) |
8.33 ± 0.37 |
8.52 ± 0.18 |
8.26 ± 0.25 |
| TSS (°Brix) |
14.62 ± 0.24 |
14.10 ± 0.25 |
13.68 ± 0.30 |
| TA (g/100mL) |
0.84 ± 0.07 |
0.82 ± 0.04 |
0.92 ± 0.01 |
| Starch conversion (%) |
48.6 ± 7.1 |
52.4 ± 14.6 |
44.0 ± 6.82 |
Ceres
| Parameter |
Site 1 |
Site 2 |
Site 3 |
| Skin background colour (1–5) |
3.01 ± 0.14 |
2.99 ± 0.02 |
2.87 ± 0.11 |
| Firmness (kg) |
8.54 ± 0.27 |
8.18 ± 0.23 |
8.61 ± 0.23 |
| TSS (°Brix) |
13.93 ± 0.44 |
14.45 ± 0.40 |
14.03 ± 0.17 |
| TA (g/100mL) |
0.96 ± 0.04 |
1.09 ± 0.04 |
1.07 ± 0.08 |
| Starch conversion (%) |
37.6 ± 8.7 |
49.8 ± 17.0 |
42.4 ± 6.2 |
Internal Browning (IB) Observations
- IB observed at all Grabouw sites (Sites 1, 2, 3).
- IB also observed at Ceres sites (Sites 1, 2).
Fruit Quality Parameters
- Skin background colour and firmness were measured for Site 1, Grabouw.
Soft Scald
- Observed in all sites for DPA+RA and RA after 6 months + 6 weeks RA + 14 days shelf-life.
- At two sites, all treatments showed soft scald after 9 months + 6 weeks RA + 7 days shelf-life.
- Also found in DPA+HCA after various periods.
Discussion
- Application of DPA did not prohibit IB development—diffuse browning still occurred.
- High CO₂ levels did not cause IB related to CO₂ damage.
- Variables included to induce IB:
- Sites with a historic browning problem
- Storage at -0.5°C instead of the recommended 1°C
- This season included a standard recommended treatment:
- 1-MCP + CA at 1°C (CA: 1.5% O₂ + 0.5% CO₂)
Acknowledgements
- Funders: ARC, HortgroScience
- Technical assistance: Howard, Viole, and Vanessa
