LONGAN COOL STORAGE AND SULPHUR DIOXIDE TRIALS
SCIENTIFIC NAME: Euphoria longana
FAMILY: Sapindaceae
Longan (Euphoria longana) is one of the tropical tree crops identified to have commercial potential in Australia. The original cultivar introduced by the Chinese miners in the last century was of poor quality. In the late 1970s, 20 different longan cultivars were introduced into Australia by the Queensland Department of Primary Industries and New South Wales Department of Agriculture (Winston and O'Farell, 1989). Among these, a few showed promise, although no firm recommendation has been made. Anticipating the potential growth of this crop, and the lack of postharvest information available, work on longan was undertaken. O'Hare and Prasad (1989) conducted a cool storage trial and suggested 10°C was optimum for short term storage. Following on from that, we conducted a trial using longan cv. Chompoo stored at selected temperatures (5, 7.5, 10, 12.5 and 15°C). There were two replicates per temperature per removal. Fruit were removed at weekly intervals for 5 weeks and evaluated for skin colour using hunter labscan, general eating quality assessed by 12 tasters and number of diseased fruit recorded. The data has not been fully analysed as yet. Fruit at 5 to 7. 5°C maintained acceptable eating quality for 5 weeks, though significant browning of the skin was noted. At 12. 5°C and 15°C, all fruit were diseased after 4 and 2 weeks in storage.
A second trial was also conducted to evaluate the potential of Metabisulphite (SO2) pads on the keeping quality of longan. Sulphur dioxide fumigation of longan has been trialled in Thailand. Earlier work conducted in this laboratory indicated there was some tainting associated with SO2 treatment. Fruit were sorted and packed in plastic punnets with either one SO2 pad or two SO2 pads and stored at 10°C. At 2 and 4 weeks after storage, samples of fruit were removed and evaluated for skin colour, general eating quality and number of diseased fruit. Sulphur dioxide pads were removed two days prior to assessment.
Visually, two SO2 pads maintain better general appearance. More unacceptable fruit were found in punnets with one SO2 pad than with no SO2 pad or two SO2 pads. Tainting was less obvious in SO2-treated fruit after 4 weeks in storage at 10°C. Data is still being assessed.
A triangle taste panel test was also conducted. 80% of tasters could detect tainting in longan packed with one SO2 pad for 1 week.
DATE: March 1990
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