Presenter: Anél Botes
Event: CA Meeting – 5 November 2019
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, a higher incidence of IB has been observed in South African ‘Fuji’ apples, possibly linked to the discontinuation of DPA use.
Aim and Objectives
- 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’ apples (2017 and 2018)
- 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
- SF + CA at 1°C (2018)
- Storage temperature: -0.5°C
- Fruit quality evaluations: After 3, 6, and 9 months storage (+ 6 weeks RA + 7 and 14 day shelf-life)
Fruit Quality Parameters
- Total soluble solids (TSS)
- Titratable acidity (TA)
- Firmness (kg)
- Skin colour (scale 1–5)
Sensory Evaluation
- Appearance (1–10)
- Taste (1–10)
- Texture (1–10)
- Off-taste (1–10)
Physiological Disorders
- Internal browning (%)
- All other internal and external disorders
Results and Discussion
Maturity Index at Harvest
| 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 |
2017 & 2018 Results
- Internal browning (IB) observed at all sites in both years.
- Skin background colour and firmness measured for Site 1.
- Senescent scald:
- 2017: All sites, DPA+RA and RA after 6 months + 6wk RA + 14d; at two sites, all treatments after 9 months + 6wk RA + 7d; also found in DPA+HCA after various periods.
- 2018: All sites, DPA+RA and RA after 6 months + 6wk RA + 14d.
Conclusions
- Application of DPA did not prohibit IB development (diffuse or radial browning).
- 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
- Importance of step-wise cooling is evident.
Acknowledgements
- Funders: ARC, HortgroScience
- Technical assistance: Howard, Viole, and Vanessa