Pg. 76-79 The effect of packaging and biological disease control on the retention of litchi colour and quality

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 addresses the need for alternatives to sulphur fumigation for postharvest litchi fruit quality maintenance due to strict EU regulations and health concerns.
• Postharvest browning of litchi is mainly caused by desiccation and polyphenol oxidase (PPO) activity, leading to irreversible colour loss and loss of phenolics.
• Polypropylene bag packaging with anti-mist and microperforations plus punnets lined with absorbent paper were tested to reduce water loss, condensation, and damage to fruit during storage.
• Biological control agents Biosave (containing Pseudomonas syringae) and F10 (a quaternary ammonium compound) were evaluated for postharvest decay control.
• Fruit was stored at 1°C and 5.5°C for up to 40 days and evaluated periodically for water loss, colour retention, PPO activity, disease incidence, and general quality.
• Packaging in polypropylene bags significantly reduced water loss to below 5%, compared to 10-14% in unpackaged fruit, preserving fruit mass and appearance.
• Fruit in punnets within the polypropylene bags showed reduced surface damage and lower incidence of disease, likely due to less free water and physical protection.
• Storage at the higher temperature (5.5°C) resulted in better colour retention but increased disease incidence; 1°C storage reduced disease but caused more colour loss, possibly due to chilling damage.
• PPO activity was higher in browned fruit and lower in well-coloured fruit, linking PPO enzymatic activity to phenolic degradation and browning.
• Biosave at 100 mL/L applied postharvest combined with punnet packaging and storage at 1°C produced the least disease incidence and best pathogen control.
  F10 was less effective than Biosave for disease control.
• Overall, the combination of absorbent-lined punnets in polypropylene bags with Biosave treatment shows promise for extending litchi shelf life and quality without sulphur use, supporting export potential.
• Further research is needed to extend storage beyond 30 days while maintaining colour and controlling disease.