Pg. 71-75 Prediction and improvement of storage potential of South African litchi fruit in the country of import

The first aim of this study was to develop a procedure to predict the length of time a specific consignment of litchis can be safely stored in the country of import. The second aim was to develop techniques that can be used by the importer to lengthen the storage period. In terms of prediction, it proved to be quite helpful to store a sample of litchis at 5°C followed by inspection on a daily basis. When the very first signs of fungal infection appear in this sample, the exporter can assume that similar symptoms will develop in the consignment, stored at 1°C, within 7 to 10 days. In terms of the inhibition of fungal growth, three techniques were evaluated. The first two of these, namely controlled atmosphere (CA) storage and disinfectant fogging, were unsuccessful. On the other hand, the addition of SO₂ sheets in the country of import proved to be quite effective. These sheets reduced fungal infection by up to 60% until day 35. However, by day 45 the sheets became ineffective. Further research should aim to establish whether additional SO₂ sheet applications should be done. A practical technique to insert the sheets into the pallet, without unpacking the boxes, must also be developed.

Summary:

• The study aimed to develop a method to predict how long a consignment of South African litchis can be safely stored in the importing country and to find ways to extend this storage period.
• For prediction, storing a sample of litchis at 5°C with daily inspection for the first signs of fungal infection was effective. Once infection appears in this sample, similar infection is expected in the main consignment (stored at 1°C) within 7 to 10 days.
• The study evaluated four prediction techniques: respiration rate, SO₂ levels in the cold room, catabolic gene markers, and differential temperature storage of indicator samples.
• Respiration rate and SO₂ level measurements proved impractical for prediction, and gene marker analysis results were pending.
• Differential temperature storage of indicator samples was successful for predicting storage duration.
• For extending storage life, three fungal growth inhibition techniques were tested: controlled atmosphere (CA) storage, disinfectant fogging, and insertion of additional SO₂ sheets at the import country.
• CA storage and disinfectant fogging applied after 25 days of regular storage were ineffective.
• Adding SO₂ sheets in the importing country was effective, reducing fungal infection by up to 60% until day 35 of storage at 1°C; however, the effectiveness declined by day 45.
• SO₂ sheets release sulfur dioxide gradually, binding to the fruit surface and inhibiting fungi.
• SO₂ residue levels in the fruit remained below the 10 ppm safety limit for most samples, although some early-season issues with residues were linked to harvest and fumigation timing.
• Further development is needed for practical methods to insert SO₂ sheets into pallets without unpacking fruit boxes during import storage.
• The study recommends using indicator samples stored at elevated temperatures as an early warning system and applying SO₂ sheets to prolong shelf life in the importing country.
• The research highlights the need for further refinement of storage extension techniques and residue monitoring to ensure fruit quality and safety.