Pg. 19-20 An Update on Commercial SO₂ Treatment of Export Litchi Fruit

A description is given of SO₂ analyses made on commercial samples and adjustments by the South African industry to new residue standards promulgated in France. Fumigation of poorly coloured or “green” fruit is strongly critisised, as this fruit does not acquire good colour during export, and therefore has a negative effect on overseas markets.

Summary:

• The article discusses sulfur dioxide (SO₂) residue analyses on commercial litchi samples and adjustments made by the South African litchi industry following France’s new stricter residue standards for imported litchis, reducing tolerance from 20 ppm to 10 ppm in the fruit pulp.
• Extensive SO₂ residue testing was done in the 1990/91 and 1991/92 export seasons from packhouses in Northern and Eastern Transvaal regions.
• Initial findings showed that SO₂ residue limits were often exceeded, especially in Madras cultivar litchis, prompting reductions in SO₂ dosage and fumigation times.
• After adjustments, most shipments complied with the 10 ppm limit, although some Madras samples still exceeded limits early in the season.
• SO₂ residue levels vary widely immediately after fumigation, with levels typically high in the peel (900-1700 ppm) but not directly correlated with pulp residue levels.
• SO₂ residues in the pulp break down significantly during cold storage and sea shipment simulation, usually falling below tolerance limits after one to four weeks.
• The article strongly criticizes fumigating immature or “green” litchis, as these fruits do not develop good color during storage and shipping, resulting in poor market quality and overseas complaints.
• Experiments with green versus mature red fruits showed that early-picked green fruit results in substandard export quality after shipping simulation.
• The study highlights the need for careful fruit maturity selection and SO₂ fumigation management to meet residue standards and maintain export fruit quality.
• The work was funded by the South African Litchi Growers’ Association and involved collaboration with agricultural technical services and quality control labs.