Sulfur dioxide fumigation in postharvest handling of fresh longan and lychee for export. [Conference paper]
1994
Sing, C.T. (Thailand Inst. of Scientific and Technological Research, Bangkok. Postharvest Technology Lab.)
Sulfur dioxide (SO2) applied as a fumigant effectively controlled saprophytic surface fungi and prevented skin browning, two of the major postharvest problems of harvested fresh longan and lychee. A standardised procedure using gaseous SO2, whereby a ratio of 5:1 between the free space volume (mL or L) of the fumigation chamber and fruit weight (g or kg) was employed. The effect of SO2 on surface growth of fungi, SO2 injury to the rind, and SO2 residue levels in the treated fruit depended on the concentration of SO2 applied, and varied with cultivar, particular crop, and the duration of fumigation. From 30-60 percent of applied sulfur dioxide was absorbed by the fumigated fruit. Maximum efficacy was obtained when whole fruit residues immediately after fumigation were 200-350 ppm. Residues were concentrated in the skin. Levels in the fruit aril were very low. A maximum residue level (MRL) of 30 ppm for the fruit aril is proposed. There is scope for a choice of application system for commercial fumigation facilities, but whatever the application system, fumigation facilities must include a scrubbing system to reduce the operator and environmental hazards associated with the use of SO2. A range of SO2 slow-release pads have been developed which are suitable for the control of skin browning and disease in lychee and longan over a range of storage and transportation times.
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