Pg. 26-30 Litchi post-harvest preservation using packaging and biological control techniques

The majority of litchi fruit produced in South Africa is treated post-harvest with sulphur to decrease fruit browning and control post-harvest diseases. However, 79% of exported fruit are sold in the European Union, which has deemed sulphur to be unacceptable. Alternative forms of fruit quality maintenance are thus necessary. The primary cause of fruit post-harvest browning is believed to be desiccation. Previous work using PVC bag packaging has, however, resulted in enhanced postharvest fungal decay, due to excessive condensation. In the work reported on in this paper, 2 sites of origin were used, with a total of 3 harvest dates. Fruit were packaged in polypropylene bags, with specific anti-mist and gas exchange properties. Three atmosphere environments within the bags were tested, while unpackaged (standard carton) fruit were used as controls. For post-harvest decay control, a systemic resistance inducer applied pre- and post-harvest, as well as a microorganism containing component were tested. Fruits were stored at 1 °C for 30 days, with evaluations at 10-day intervals. Packing in bags significantly reduced fruit water loss and enhanced retention of fruit colour for up to 20 days, while control fruits were brown within 10 days. There was no advantage of modified atmosphere over standard atmosphere packaging. Most water loss occurred during the first 10-day period of storage. No measurable decay was found within the context of the study.

Summary:

• South African litchi fruit are mostly treated post-harvest with sulphur to reduce browning and decay, but sulphur is banned by the European Union, necessitating alternative preservation methods.
• The primary cause of browning in litchi is desiccation; controlling water loss is key to maintaining fruit quality.
• Previous PVC bag packaging reduced browning but increased fungal decay due to condensation issues.
• This study tested polypropylene bags with micro-perforations for gas exchange and anti-mist coating to reduce water loss while limiting condensation.
• Biological control treatments included systemic resistance inducers (ISR2000) and a microbial product (Biosave) applied pre- and post-harvest for decay control.
• Fruit were stored at 1°C for 30 days, with evaluations every 10 days for water loss, color retention, and decay.
• Packaged fruit consistently lost significantly less water (2-3%) than non-packaged fruit (10-14%) over 30 days, with most water loss occurring in the first 10 days during cooling.
• Packaged fruit maintained red color and overall appearance up to 20 days, whereas non-packaged fruit browned within 10 days.
• No significant advantage was found between modified atmospheres and standard atmosphere packaging under the tested conditions.
• ISR2000 and Biosave had no clear effect on water loss or color retention, though ISR2000 pre-harvest application may enhance color through anthocyanin stimulation.
• No measurable post-harvest decay developed in the study, likely due to the low storage temperature inhibiting pathogens.
• The study suggests cooling methods like hydro-cooling prior to packaging could further reduce water loss and improve shelf life.
• Future work is needed to optimize storage temperature based on market needs, evaluate biological control effectiveness under warmer conditions, and continue development of integrated post-harvest pathogen management.
• Overall, polypropylene bag packaging is effective in extending litchi shelf life by minimizing water loss and maintaining color, making it a promising sulphur-free preservation technique.