Articles
IMPROVED SULFUR DIOXIDE FUMIGATION OF FRESH LONGAN USING A VERTICAL FORCED-AIR TECHNIQUE
Article number
880_49
Pages
415 – 422
Language
English
Abstract
The problem of high sulfur dioxide (SO2) residues on fresh longan (Dimocarpus longan Lour.) remains persistent in Thailand because of inefficient fumigation technology.
An improved SO2 fumigation process has been developed for longan by applying a vertical forced-air technique to reduce usage of SO2. An experiment was conducted using a vertical forced-air column at three air flow rates of 0.6, 0.8 and 1.0 m3/s, with two types of basket, (rectangle and trapezoidal shaped baskets), capable of holding 550 and 660 kg of longan per batch, respectively.
During the fumigation process, SO2 with an initial concentration of 10,000-12,000 ppm was circulated through the forced-air column inside the fumigation chamber for about 60 min.
After being absorbed by longan fruit, the SO2 concentration decreased to the final concentration of 4,000 ppm, at which time the fumigation process was terminated.
Quality and shelf-life of fresh longan were determined every fifth day during storage at 2°C and 95%RH. Forced-air fumigation at all air-flow rates effectively prevented postharvest diseases and browning of fresh longan for at least 20 days.
Air-flow rate and basket type were not significant factors (p≥0.05) affecting SO2 residue on longan peel and pulp, which was within the range of 1,600-1800 mg/kg and 5 mg/kg immediately after fumigation respectively.
The SO2 concentration used in this work was 3 to 5 times lower than the official recommendations commonly practiced by longan processors.
It is suggested that a minimum air flow rate of 0.6 m3/s (or 3.27 m3/h/kg-produce) should be applied to obtain minimal SO2 residues with this vertical forced-air technique.
Vertical forced-air SO2 fumigation offers enhanced effectiveness for commercial practice with a trapezoidal shaped basket where the SO2 flow-thru is much weaker than the tunneled or horizontal forced-air technique.
An improved SO2 fumigation process has been developed for longan by applying a vertical forced-air technique to reduce usage of SO2. An experiment was conducted using a vertical forced-air column at three air flow rates of 0.6, 0.8 and 1.0 m3/s, with two types of basket, (rectangle and trapezoidal shaped baskets), capable of holding 550 and 660 kg of longan per batch, respectively.
During the fumigation process, SO2 with an initial concentration of 10,000-12,000 ppm was circulated through the forced-air column inside the fumigation chamber for about 60 min.
After being absorbed by longan fruit, the SO2 concentration decreased to the final concentration of 4,000 ppm, at which time the fumigation process was terminated.
Quality and shelf-life of fresh longan were determined every fifth day during storage at 2°C and 95%RH. Forced-air fumigation at all air-flow rates effectively prevented postharvest diseases and browning of fresh longan for at least 20 days.
Air-flow rate and basket type were not significant factors (p≥0.05) affecting SO2 residue on longan peel and pulp, which was within the range of 1,600-1800 mg/kg and 5 mg/kg immediately after fumigation respectively.
The SO2 concentration used in this work was 3 to 5 times lower than the official recommendations commonly practiced by longan processors.
It is suggested that a minimum air flow rate of 0.6 m3/s (or 3.27 m3/h/kg-produce) should be applied to obtain minimal SO2 residues with this vertical forced-air technique.
Vertical forced-air SO2 fumigation offers enhanced effectiveness for commercial practice with a trapezoidal shaped basket where the SO2 flow-thru is much weaker than the tunneled or horizontal forced-air technique.
Authors
J. Phimphimol, J. Varith, S. Jaturonglumlert, P. Chommuang, K. Kubnop
Keywords
fresh longan, sulfur dioxide, vertical forced-air technique
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