Pg. 36-38 Control of Post-Harvest Decay and Browning of Litchi Fruit by Sodium Metabisulphite and Low pH Dips – An Update

Fruit of cultivars Mauritius and Madras were treated experimentally and semi-commercially with a sodium metabisulphite dip, followed by low pH dips. Disease incidence, browning, colour and taste of fruit of different treatments were compared. Sodium metabisulphite gave the best experimental results for both cultivars, as well as semicommercially on Mauritius fruit, but was disappointing semi-commercially on Madras fruit (probably due to poor fruit quality).

Summary:

• The study involved treating litchi fruit cultivars Mauritius and Madras with sodium metabisulphite (Na₂S₂O₅) dips followed by low pH dips (hydrochloric acid, acetic acid, or vinegar) to control postharvest decay and browning.
• Experimental and semi-commercial trials were conducted, comparing disease incidence, browning, color, taste, and SO₂ residues in treated fruit.
• Sodium metabisulphite dip followed by a 5-minute hydrochloric acid dip gave the best results in controlling decay and browning, especially for Mauritius fruit.
• For Mauritius fruit, this treatment also maintained better color and taste compared to other treatments, including commercial SO₂ fumigation.
• Madras fruit responded less well to sodium metabisulphite treatments, with higher browning around the stem end compared to SO₂ fumigation, possibly due to poorer fruit quality influenced by drought stress.
• SO₂ fumigation was more effective in reducing browning and disease in Madras fruit, but sodium metabisulphite treatments resulted in less sulfur residue in the fruit pulp.
• Low pH dips alone were less effective than the combination with sodium metabisulphite in controlling browning and decay.
• Semi-commercial treatment of Mauritius fruit with sodium metabisulphite and hydrochloric acid provided good control of postharvest issues, but results for Madras fruit were disappointing, again likely linked to fruit quality.
• The study concluded that sodium metabisulphite combined with low pH dips could be a viable alternative to SO₂ fumigation for controlling postharvest decay and browning if fruit quality is good.
• SO₂ fumigation remains preferable when fruit quality is poor, especially for the Madras cultivar.
• The fruit were stored at 1°C for 28 days, then evaluated for browning, disease, color, and taste after 3 days at 20°C.
• Residual sulfur dioxide was only detected in SO₂-fumigated fruit pulp, while sodium metabisulphite treatments showed no significant residue.
• The research emphasized the importance of fruit quality for postharvest treatment success.