Good news for the sandwich lovers - if canned fish and tuna are your favourite filling.
A total of 43 samples of canned fish and tuna sandwiches have been put to test in a joint study of the Consumer Council and the Food and Environmental Hygiene Department.
The result: They were found to be safe from food poisoning or, more precisely, histamine poisoning.
This reassuring outcome is particularly welcoming these days to consumers beset by periodic reports of food scare of one kind or another.
Histamine is a chemical compound that forms in the muscle of dead fish (in scombroid fish species such as tuna and mackerel as well as non-scombroid species such as sardine and anchovy).
It is difficult, if not impossible, for a consumer to tell a fish with high histamine content, by appearance or odour. The chemical also could not be destroyed by heat.
Consumption of fish containing a high concentration of histamine causes foodborne intoxication, known as histamine poisoning.
It is usually a mild disorder with a variety of symptoms such as tingling and burning around the mouth, facial flushing and diarrhoea.
As such the condition is not easily recognized and poisoning cases often may go unreported. In Hong Kong, food poisoning due to histamine is reported sporadically.
The study sought to (a) determine the levels of histamine in canned fish and tuna sandwiches available at various retail and sandwich outlets, and (b) explore measures on reducing the risks associated with histamine in fish.
Included in the test were 23 samples of canned fish (12 tuna, 5 sardine, 3 mackerel and 3 anchovy) and 20 samples of tuna sandwiches.
Currently, there is no specific regulation on the histamine level in canned fish and its products in Hong Kong. But according to Codex Alimentarius Commission (CODEX), histamine level of canned fish should not exceed 200 mg/kg.
The test gave the samples a clean bill of health: all were within and far below the CODEX standard on histamine levels.
Among the 23 canned fish samples, six were not detected with histamine, and the other 17 were found to contain histamine ranging from 0.7 mg/kg to 6.9 mg/kg.
For the 20 tuna sandwich samples, two were undetected with histamine, and the other 18 were shown to contain histamine ranging from 0.6 mg/kg to 20 mg/kg.
So, consumers can put your heart at ease, and continue to savour their delightful canned fish and tuna sandwiches from various outlets.
Nonetheless, as clearly indicated in the study, the possibility of histamine formation depends crucially on proper storage of the canned fish once opened for consumption.
In the second part of the study, opened canned tuna was stored at three different temperatures - 2℃; 22℃ to 23℃ (room temperature); and 33℃ (common kitchen temperature) - of different time intervals for analysis.
The analysis found that the chance of histamine formation in opened canned tuna could be substantially reduced if stored properly under refrigeration.
On the contrary, if stored at 33℃ for six hours, the level of histamine escalated rapidly in excess of the CODEX standard of 200 mg/kg reaching the toxicity level.
Both the food industry and consumers are urged to handle opened canned fish properly to avoid the formation of large amount of histamine leading to poisoning. Here is some useful advice:
- Purchase only from reputable stores.
- Avoid prolonged storage of opened canned fish. Any remainder should be properly wrapped and stored in refrigerator (at 4℃ or below), and finished within one or two days. They should be separated from raw food in storage.
- Pay attention to the "use-by" date and storage condition when purchasing of tuna sandwiches, for example, the temperature of the refrigerator.
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