- L Tait and F J Kruger
- Institute for Tropical and Subtropical Crops, Private Bag x11208, Nelspruit 1200
- 1999
A study was conducted to evaluate a range of potentially effective post-harvest treatments for HLH Mauritius and McLeans Red litchis. The results indicated that the two cultivars require completely different research approaches. Good results were achieved with sulphur free treatments for HLH Mauritius and well structured semi-commercial trials under the auspices of the research team are recommended. Poor results were, however, attained with McLean’s Red. Not only did the currently applied techniques result in poor shelf life, but sulphur residues were unacceptably high in certain cases. It is therefore proposed that, in the coming season a thorough epidemiological survey should be conducted with the aim of optimizing the currently applied techniques.
Summary:
- The study evaluated various post-harvest treatments for two litchi cultivars: HLH Mauritius and McLeans Red, finding that the cultivars require different research approaches.
- HLH Mauritius showed good results with sulphur-free treatments and is recommended for semi-commercial trials, while McLeans Red had poor results, including poor shelf life and high sulphur residues.
- Four groups of post-harvest studies were identified: sulphur residue surveys, alternative sulphur sources, sulphur-free preservation techniques, and techniques to improve litchi storage regardless of preservation methods.
- Research priorities included factors affecting post-harvest quality such as packinghouse hygiene, sulphur dioxide application methods, steam and hot water treatments, relative humidity, fungicides, coatings, modified atmospheres, acid treatments, antioxidants, temperature regimes, and cooling methods.
- Nine trials were conducted during the 1997-8 season:
- HLH Mauritius trials showed successful retarding of browning and fungal infections using sulphur fumigation, acid washes, and steam treatments.
- McLeans Red trials showed difficulties with colour retention, fungal infections, and internal browning caused by acid treatments.
- Sulphur fumigation improved external colour and decreased fungal infections but did not entirely prevent them.
- Fungicide treatments showed poor effectiveness compared to sulphur.
- Ultrasonic treatments prior to acid dips improved external appearance and reduced fungal infections.
- Biological coatings (Wilt Pruf) helped slow moisture loss but were effective mainly when combined with prior sulphur fumigation.
- Antioxidant treatments were ineffective and hampered acid treatment benefits.
- Sulphur residue levels in McLeans Red are higher and persist longer than in HLH Mauritius, posing potential export concerns due to strict allowable residue limits in importing countries.
- Recommendations include:
- Conducting export trials with sulphur-free HLH Mauritius fruit treated with hydrochloric acid and other pre-treatments.
- Conducting epidemiological surveys and quality control in packinghouses for McLeans Red.
- Investigating sulphur residue impact on exports and identifying factors influencing high sulphur retention in McLeans Red.
- Screening alternative biological-friendly post-harvest agents for effective fungal control.
- The article also references several studies on sulphur residue levels and post-harvest treatments confirming the need for cultivar-specific approaches for post-harvest litchi management.