Pg. 25-28 Maintaining Market Quality of Litchis Overseas Without SO₂

Gas packaging in 5, 10 and 20 per cent Freshpak^® , controlled both browning and decay in fresh litchis – cultivars Mauritius and Madras – stored for 28 days at 1°C plus a further three days at 20°C. However, the skin turned brown once fruit were removed from the packaging after the 31-day storage period. Litchis that were gamma-irradiated were found to be more susceptible to decay development than untreated fruit.

Summary:

• The article explores non-chemical alternatives to sulphur dioxide (SO₂) fumigation for controlling browning and decay in fresh litchis during storage and export.
• Research tested treatments including gamma irradiation and modified atmosphere packaging (MAP) with gas mixes containing CO₂ in nitrogen (Freshpak) and plastic films (Vitafilm).
• Gamma irradiation at doses of 0.75 kGy and 1.5 kGy increased susceptibility to decay, likely due to skin damage, but a hot water dip before irradiation reduced this effect.
• Packaging litchis in Vitafilm significantly reduced browning compared to untreated fruit after 28 days storage at 1°C plus 3 days at 20°C.
• MAP treatments with 5%, 10%, and 20% CO₂ concentrations in combination with polyethylene effectively controlled browning and decay, especially in the Madras cultivar.
• Decay incidence was low during the study season, probably due to dry weather, so results should be repeated for confirmation.
• Upon removal from controlled atmosphere packaging after 31 days, litchis exposed to normal air browned quickly due to enzyme reactions triggered by oxygen exposure.
• The study emphasizes exploring gas mixes with small amounts of oxygen in further MAP research to better control browning after storage.
• SO₂ use has drawbacks including overdose risk, sulphur taste, and ineffective decay control against some fungi, motivating the search for alternatives.
• Moisture loss promotes browning by causing enzymatic reactions that degrade the red pigment (anthocyanin) in litchi skin; plastic packaging reduces moisture loss.
• Fungicide dips have shown some promise but have associated issues with residues and taste, with limited interest in registration due to the small litchi market.
• The study concludes MAP with CO₂ gas mixes and proper packaging shows promise for maintaining market quality of litchis overseas without SO₂ fumigation.