Pg. 37-40 Alternative treatments to replace sulphur dioxide fumigation

Investigations on developing alternative treatments to replace sulphur dioxide fumigation were carried out during the 2004/05 growing season. This study was confined to the major export cultivar McLean’s Red. Modified Atmosphere Packaging (MAP) was used in combination with hot water treatments to retain the postharvest quality of litchi fruit during long-term storage. Fruit were exposed to 50°C x 2 min, 55°C x 1 min and 60°C x 1 sec regimes; blower dried for 3 min; packed in MAP, heat sealed and stored at 2°C and 95% RH for 40 days. Quality assessment indicated that hot water dips at high temperatures affected the colour retention of the fruit. The light intensity, L, chroma C, colour coordinates a and b showed a decline, while the hue angle H₀ showed an increase. Exposure to higher temperatures affected the fruit firmness and higher weight loss was observed. Soluble solids concentration (Brix) was low and titratable acidity was high in fruit exposed to higher temperatures. Although hot water dip treatments combined with MAP minimized the incidence of fungal decay, higher decay incidence was observed at 50°C. It was evident from this study that fruit stored in MAP alone without any hot water dip treatment retained quality the most effectively.

Summary:

• The study investigated alternative postharvest treatments to replace sulphur dioxide (SO₂) fumigation for litchi fruit, focusing on the McLeans Red cultivar during the 2004-05 season.
• SO₂ fumigation, although effective, leaves undesirable residues, affects taste, and poses health risks, especially for sulphur-sensitive consumers and workers.
• Alternatives tested included Modified Atmosphere Packaging (MAP) combined with hot water treatments at various temperatures (50°C for 2 min, 55°C for 1 min, and 60°C for 1 sec).
• Hot water dips affected fruit color retention (pink-red color faded), firmness, and caused higher weight loss at higher temperatures.
  MAP alone without hot water treatment retained fruit quality best over 40 days at 2°C and 95% relative humidity.
• Disease incidence was minimal in fruit packed in MAP and in those treated with 60°C x 1 sec dip, while 50°C x 2 min dipped fruit showed higher decay.
• SO₂ fumigated fruit showed higher soluble solids concentration (Brix) and titratable acidity due to senescence and microbial activity.
• Hot water treatments can reduce fungal decay but are sensitive to temperature and exposure time; effectiveness depends on cultivar and pericarp thickness.
• The study highlighted the need for environmentally friendly, safe, and economically viable postharvest treatments to maintain fresh appearance, natural color, and taste over extended storage and transportation.
• MAP helps retain fruit quality by reducing moisture loss and maintaining pericarp pH, which prevents browning and decay.
• The findings suggest that hot water combined with MAP and other treatments may offer a commercial alternative to SO₂ fumigation but require optimization to minimize adverse effects on fruit quality.