Pg. 46-49 Refinement of the maturity cut off points for sulphur fumigated HLH Mauritius litchi fruit

During the 2003/04 season, a study was launched with the aim of formulating appropriate maturity cut-off points for South African export litchi fruit. The results revealed that in the Nelspruit area, sulphur fumigated fruit must not be exported after the 30: 1 (TSS:TA) point is reached. During the 2004/05 season, the trials were continued in the important Onderberg production region. The results indicated that, in this region, it is possible to export the fruit up to the 40: 1 stage. After this, fungal infections became a serious problem. During each experiment, slow release SO₂ sheets were placed in three positions in the boxes (in the bottom, on top of the fruit and both sides). A sheet on the bottom of the box was found to considerably improve the storage potential of the fruit. In contrast with the Nelspruit area, sulphur residues did not become a problem towards the end of the harvest window.

Summary:

• A study during the 2003/04 season aimed to define appropriate maturity cut-off points for South African export litchi fruit using the total soluble solids to titratable acid (TSS:TA) ratio as a maturity index.
• In the Nelspruit area, sulphur fumigated litchis should not be exported after reaching a 30:1 TSS:TA ratio, as fruit maturity beyond this point negatively impacts storage and quality.
• Trials in the 2004/05 season in the Onderberg production region showed that fruit could be exported up to a 40:1 TSS:TA ratio, but fungal infections become a serious problem beyond this maturity level.
• Slow release sulfur dioxide (SO₂) sheets were used in packaging at different box positions (bottom, top, and both sides), with bottom placement significantly improving fruit storage and reducing fungal infections.
• Unlike in Nelspruit, sulphur residues on the fruit were not problematic at the end of the harvest window in the Onderberg region.
• Fruit was stored at 1°C for 28 days followed by evaluations on shelf life for fungal infection, TSS, titratable acids, and appearance.
• The fungal infection rate remained low up to around a 40:1 TSS:TA ratio, increasing sharply afterward.
• SO₂ sheets complement sulphur fumigation by reducing fungal infections, with bottom or both-sides placement being more effective than top placement.
• Sulphur residue levels in the aril stayed within the EU’s maximum residue limits, though pericarp residues rose towards the season’s end but stayed below regulatory limits.
• Recommendations include using a 30:1 maturity cut-off for Nelspruit fruit and 40:1 for Onderberg fruit, using one slow-release SO₂ pad placed at the bottom of the carton.
• It is emphasized that cut-off points can vary due to other pre- and postharvest factors and that producers should control sulphur residue through adequate packinghouse measures.