Pg. 25-30 Development and Refinement of Litchi Postharvest Treatments

A number of trials aimed at developing new litchi postharvest storage treatments were conducted during the last season. In the most important of these, dip treatments with “acid A” and “acid B” were evaluated. The “acid A” trial was conducted with HLH Mauritius while the “acid B” trial was done with both HLH Mauritius and McLean’s Red fruit. Overall, “acid B” showed considerable promise in that the fruit were firm with a freshly picked appearance after 25 days of cold storage. Sensory analysis revealed the tasting panel to prefer the “acid B” treatment to the standard SO₂ treatment. However, certain panellists recorded a slight “sharpness on the tongue”. As with all previous methods, this treatment was found to be damaging to the aril of McLean’s Red fruit. On the whole, we consider this method to be the most promising alternative to sulphur fumigation of HLH Mauritius and further experimentation is definitely justified. In addition to the above trials, detailed experiments were conducted to upgrade and refine the presently used sulphur fumigation/HCI dip regime. The use of controlled atmosphere was also further pursued and good experimental and semi-commercial results were attained with this technique.

Summary:

• Multiple trials were conducted to develop improved postharvest storage treatments for litchi, focusing on sulphur-free preservation techniques.
• The major trial evaluated dip treatments using two acids, with “acid B” showing superior results to standard sulphur dioxide (SO₂) fumigation, maintaining firmness and fresh appearance after 25 days of cold storage.
• Sensory analysis favored the acid B treatment over SO₂, though some panelists noted a slight sharpness on the tongue; damage to the aril was an issue for certain cultivars.
• Existing sulphur fumigation and pH1 hydrochloric acid (HCl) dip regimes were refined, revealing that 4–6 minute dips are optimal for color retention without excessive loss of firmness, while longer dips increased mass loss and risked skin damage.
• Controlled atmosphere (CA) storage was tested and found to reduce fungal infection and mass loss compared to room atmosphere (RA) storage, while also maintaining acid levels in fruit; however, careful management of sulfur residues is needed for export standards.
• Pilot trials using alternative acids revealed acid B at pH 0.75 for 10 seconds as optimal, providing promising color retention, firmness, and minimal fungal infection or acid loss.
• The Agricoat coating formula acidified with acid B matched the dip’s color retention but resulted in lower firmness, indicating limited commercial benefit.
• Panelists overwhelmingly preferred acid B–treated fruit, with majority expressing willingness to buy, minimal aftertaste recorded, but some reported a burning sensation at higher concentrations.
• Findings support CA storage as a tool for quality retention during export seasons with high spoilage risk, especially for late season, high rainfall harvests.
• Acid B is highlighted as the most promising alternative to SO₂ fumigation for HLH Mauritius litchi, showing strong anti-fungal and color retention effects, but further research is warranted to refine the regime and eliminate taste issues.