Pg. 42-45 Effect of post-harvest storage temperature and silicon on colour retention and pathogen control of litchi (Litchi chinensis Sonn.)

Due to the need for eliminating sulphur from post-harvest treatments, alternative means of post-harvest colour retention and pathogen control are necessary. Further, access to new markets will require phytosanitary treatments which may include cold sterilisation. Previous work demonstrated that packaging could reduce water loss and extend colour retention. However, effects of storage temperature below 0°C have not been studied. For pathogen control, the GRAS compound silicon has been shown as effective for a number of crops, but sufficient information is not available for litchi. Litchi fruit were packed in punnets and sealed in micro-perforated polypropylene bags before storage at -0.5°C, 1°C or 5.5°C. Half the fruits were untreated controls, while the other half were treated with silicon in the form of SiO₂ before packaging. Evaluations for colour and fungal infections were done after 10, 20, 30 and 40 days while in storage, plus an additional 5 days at room temperature (after removal from storage). Colour retention was retained for up to 40 days, but there was a time / temperature interaction with colour retention. The cold chain needed to be retained to prevent pathogen development. Silicon did not prevent pathogen development and may damage fruit, possibly due to the pH of the dipping solution. While it has been demonstrated that long-term low temperature storage is viable, which will allow for cold sterilisation, further work on pathogen control and cold chain management is necessary.

Summary:

• The study explores alternatives to sulphur for post-harvest colour retention and pathogen control in litchi fruit, focusing on storage temperature and silicon treatment.
• Litchi fruit were stored at three temperatures: -0.5°C, 1°C, and 5.5°C, in micro-perforated polypropylene packaging with and without silicon treatment.
• Colour retention was commercially acceptable for up to 40 days at all temperatures, with 5.5°C showing the best overall colour retention and least browning.
• Storage at 1°C resulted in poorer fruit colour, while -0.5°C caused some anthocyanin degradation but still maintained acceptable quality.
• Silicon treatment did not prevent pathogen development and was associated with increased decay and faster pathogen growth, possibly due to high pH of the silicon solution damaging the fruit rind.
• Post-harvest pathogen growth accelerated rapidly when fruit was removed from cold storage and held at ambient temperature, indicating low temperatures are fungistatic but not fully fungicidal.
• Proper cold chain management and packaging to prevent water accumulation are essential for maintaining fruit quality during storage and shipping.
• The study suggests that 40-day sulphur-free storage and shipping of litchi is feasible with the right temperature and packaging protocol.
• Further research is needed on silicon formulation/application, biological control agents, and integrated approaches for improved pathogen control.
• Maintaining the cold chain up to point of sale is critical to inhibit post-harvest pathogen development and preserve fruit quality.