Pg. 12-16 Effect of Reduced Sulphur Exposure and of Controlled Atmosphere Storage on the Post-storage Quality of Madras Litchi

Controlled atmosphere (CA) storage of litchi after harvest has been reported to extend shelf-life, enhance sensory quality, and reduce or prevent disease manifestation. Sulphur treatment prevents pericarp browning, and is fungicidal. However, it is associated with the development of off-flavours and reduced pericarp colouration after extended cold-storage, and its application is meeting with consumer resistance. The present study was carried out to assess the effect on the post-storage quality of Madras litchi fruits of controlled atmosphere storage in combination with reduced post-harvest SO₂ treatment duration.

The litchis stored under CA showed greater weight loss during cold-storage. As time progressed after cold-storage, the fruits were colonised by blue mould. Nine days after cold-storage, mould colonisation was least in the fruits exposed to SO₂ for the shortest duration (500g SO₂ per MT for 15 minutes on the day of harvest), and in those having been placed under CA storage. Fourteen days after cold-storage, appreciably more fruits were healthy following storage under CA or sulphur treatment for the shortest duration. Differences in TSS in relation to atmosphere storage were not apparent. There were slight differences in this regard relating to the duration of SO₂ treatment. Taste was most appealing in the fruits having been exposed to CA storage, and having received the shortest duration of SO₂ treatment.

The results clearly favour short-duration SO₂ treatment and CA storage for Madras litchi. Fungicide treatment in addition to SO₂ treatment should be considered in view of the effect of sulphur treatment on the susceptibility of litchi fruits to blue mould colonisation.

Summary:

• Controlled atmosphere (CA) storage of litchi extends shelf-life, enhances sensory quality, and reduces disease after harvest.
• Sulphur dioxide (SO₂) treatment prevents pericarp browning and acts as a fungicide but can cause off-flavours and reduced color after long cold storage.
• Consumer resistance to SO₂ treatment is increasing, motivating research into reduced SO₂ exposure combined with CA storage.
• The study tested Madras litchi fruits exposed to four different SO₂ treatment durations (15, 18:45, 26:15, 30 minutes at 500 g SO₂ per MT of fruit) with and without CA storage at 1°C.
• Fruits under CA storage showed greater weight loss during cold storage compared to regular atmosphere storage.
• Nine days after cold storage, blue mould colonization was least in fruits treated with SO₂ for the shortest duration (15 minutes) and in CA stored fruits.
• Fourteen days after cold storage, more fruits remained healthy with CA storage or shortest SO₂ treatment.
• Total soluble solids (TSS) showed minor differences with treatment; taste was most appealing in fruits with CA storage and shortest SO₂ exposure.
• The study favors short-duration SO₂ treatment combined with CA storage for Madras litchi to prolong post-storage quality while reducing SO₂ residues and off-flavors.
• Fungicide treatment (e.g., prochloraz) is recommended alongside SO₂ to reduce susceptibility to blue mould, which SO₂ treatment alone can increase.
• The study suggests further research on reduced SO₂ concentrations and treatment times for Madras and other cultivars.
• The importance of pericarp color retention for successful export in South African Madras and Mauritius cultivars is highlighted, with SO₂ treatment effective but controversial due to health concerns and consumer resistance.