The Consumer Council has issued a cautionary health advice on the consumption of two of the season's most favourite fruits, longans and lychees.
In a test on longans, the Council has detected sulphur dioxide, used as a fumigant, on the peels of the fruit. Out of 11 batches of longan samples, nine batches were detected with sulphur dioxide ranging in quantity from 143 ppm to 453 ppm.
The chemical may provoke asthma attacks in allergy sensitive people. Also the Acceptable Daily Intake (ADI) established by the Joint FAO/WHO Committee on Food Additives recommends that a 60 kg person should take no more than 42 mg of sulphur dioxide per day.
The test samples were sourced from retail outlets in different districts including wet market stalls, fruit stores and supermarket fruit counters, with claims of countries of import from Thailand (8 batches), Australia (2 batches) and Hainan (1 batch).
The test showed that to the relief of longan lovers, the presence of sulphur dioxide was confined to the peels only as none of the longan samples had the chemical detected in the flesh.
Fresh longan flesh is prohibited to contain any preservative under the Preservatives in Foods Regulation in Hong Kong.
Consumers, however, should be wary of the risk of contamination if they immerse longans that are without an intact stalk, in water in order to remove any chemicals or dirt on the peel.
In the test, it was shown that sulphur dioxide was somehow found present in the flesh, of about 54 ppm and 60 ppm respectively in the two bundles of longans without an intact stalk which had not been detected prior to water immersion.
As sulphur dioxide is soluble in water, it is possible that the dissolved chemical could have found its way to the flesh through cracks and openings on the surface. In a similar test, longans with an intact stalk displayed no such problem.
The proper way to remove sulphur dioxide is, therefore, to rinse the longans under running tap water and wipe them dry afterwards. The test showed that though this could substantially reduce the amount of sulphur dioxide (up to 75%), it could not totally eliminate the chemical on the peel.
Consumers and in particular people sensitive to allergy are strongly advised to exercise care to avoid contamination when consuming longans: always wash hands, after peeling and before consumption; and, needless to say, never bite on longan peel or put the whole fruit into the mouth.
Lychee aficionados are also cautioned to be moderate in the intake of lychees currently in season in abundance in the market.
The Consumer Council is concerned over recent media reports about an illness allegedly caused by consuming excessive amount of the fruit.
The Council has sought the expert advice of Chinese and Western medicine practitioners. Both concurred that an illness could be induced by excessive consumption of lychees at a time.
In the view of the Chinese medicine practitioner eating lychees excessively may cause hypoglycemia leading to fever, seizure and unconsciousness; whereas the Western medicine practitioner's view is that if the subject is allergic to lychees, it may cause such severe allergic reactions as fall in blood pressure, gastrointestinal upset, respiratory distress, skin edema, dizziness and unconsciousness.
But consumers need not worry unduly as people who are not susceptible to allergic reactions to lychees, eating a normal amount of lychees should cause no problem.
Diabetes patients should, however, watch the limit the amount of lychees they consume. At the most, they may eat seven or eight pieces a day and avoid other fruit at the same time to prevent taking too much sugar.
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