Fishy Reactions
Although foodborne illness and adverse reactions are not limited to seafood, and are a common concern of all food industries, they are often associated with fish, processed fish and shellfish. But when handled properly, these foods are as safe to eat as any other source of protein. This newsletter explores the types of adverse reaction to fish and shellfish that can occur, and how the safety of fish and related products is addressed in South African legislation.
South African regulations applicable to fish and seafood
NRCS regulates the compulsory specifications for frozen fish and marine molluscs, frozen rock lobster, frozen shrimps, langoustines and crabs, and smoked snoek. The minimum requirements of these compulsory specifications are based on:
- Prerequisites for food safety: Good Manufacturing Practices (GMP) and Good Hygiene Practices (GHP)
- Standards and guidelines set by the Codex Alimentarius
- National requirements
Regarding the labelling of fish and shellfish, it is advisable to consult the Regulations on Labelling and Advertising of Foodstuffs (R. 146/2010 as amended), which fall under the Foodstuffs, Cosmetics and Disinfectants Act, 1972 (Act 54 of 1972). There are a number of other applicable regulations regulated by the Department of Health, and they are addressed in the relevant sections below. It is also important to consider the Consumer Protection Act, 2008 (Act 68 of 2008).
What are the major causes of adverse reactions to seafood and fish?
Many people associate adverse reactions to fish with allergy only. In fact, there are many types of reaction to fish, including:
Adverse reactions to fish |
|
| Allergies:
|
|
| Intolerance: |
|
| Toxic reactions: |
|
| Microbial: |
|
This newsletter will focus on the reactions to Histamine, Microbial Contamination, and Heavy Metals. Feel free to contact FACTS for information on allergic reactions to fish, or any of the other adverse reactions mentioned above.
Histamine
Fish tissue containing high levels of histamine (a biogenic amine) can cause a severe form of illness in humans, commonly referred to as histamine poisoning or scombroid poisoning. Symptoms that are similar to (and are often mistaken for) seafood allergic reactions include nausea, vomiting, diarrhoea, oral burning, hives, rashes and hypotension, and may resemble an allergy reaction. Good-quality fish generally contains <10 ppm histamine. It is suggested that most people will show symptoms of histamine poisoning when at least 2.7mg of histamine per kg of body weight is ingested; while at lower levels, only the most sensitive individuals will experience adverse reactions.
About histamine formation
The levels of histamine formed in fish post-mortem are highly dependent on the presence and concentration in the flesh of the amino acid histidine. In particular, fish of the Scombroid family (including tuna, mackerel, herring, marlin, bonito, and jacks) contain high levels of the histidine amino acid, which can be converted to toxic histamine. Nonetheless, fish from other families – such as salmon (Salmonidae), anchovies, sardines, and yellowtail kingfish – have also been reported to cause histamine poisoning.
As soon as a fish dies, the fish gill and gut bacteria will start to break down the tissue proteins, releasing histidine, which is then rapidly converted to histamine. Since bacteria multiply rapidly, it is possible for the level of histamine in the ungutted fish to double every twenty minutes. The longer a fish remains ungutted after it dies, the higher the level of histamine in its tissues. It is important to note that even when the fish has been gutted, the histamine levels will continue to increase once the enzyme is present in the fish. There can also be an uneven distribution of histamine throughout a single fish, as histamine concentration can vary considerably between anatomical locations [1].
The optimum growth temperatures of the bacteria implicated in the formation of histamine are within the range of 20 to 30°C, although some can grow below 10°C (e.g. Vibrio spp.). As stated above, once the enzyme is present in the fish, it can continue to produce histamine at refrigeration temperatures. Preventing the degradation of histidine to histamine by the rapid chilling of fish immediately after death, followed by good temperature control in the supply chain, is the most appropriate control. Once histamine is formed, it is highly resistant to tampering; so cooking, smoking, freezing, and canning cannot prevent histamine fish poisoning reactions.
South African regulations applicable to histamine levels in fish
According to the Foodstuffs, Cosmetics and Disinfectants Act, 1972 (Act 54 of 1972), Regulations governing microbiological standards for foodstuffs and related matters, R. 692 of 1997, as amended:
“Partly cooked or uncooked seawater and freshwater foods, and cooked seawater and freshwater foods such as fish containing histamine at levels of more than 10mg per 100g of foodstuffs when tested according to AOAC (Association of Official Analytical Chemists) method 977.13 (1990), shall indicate decomposition of the foodstuff. If a foodstuff contains more than 20mg per 100 grams histamine, it shall render the foodstuff unsafe for human consumption.”
Mercury-containing
The regulations relating to Marine food, R. 2064 of 1973, as amended, state that:
“Fish shall be processed as soon as possible after being caught. Where not frozen immediately, it shall be kept at a temperature not exceeding 10°C until processing commences. When being thawed for subsequent processing, frozen fish shall not be exposed to any temperature higher than 20°C, and the thawing shall be completed in less than 20 hours. Unless processed immediately after thawing is complete, the chilling of thawed fish to 0.5°C shall be commenced immediately.”
Additionally, the Regulations governing general hygiene requirements for food premises and the transport of food, R. 962 of 2012, state in annexure D that the required core temperature of unpreserved fish that is stored, transported or displayed for sale shall be +4°C.
Testing for histamine
When testing for histamine, it is important to ensure that detailed information is recorded on the temperature control in the supply chain, and that samples are kept well below 10°C, to ensure that any histamine results are not due to a break in the cold chain, and can be traced back to any incorrect handling of the samples.
Microbiological Safety of Fish and Shellfish
Seafood poisoning outbreaks have frequently been associated with bacterial contamination, such as Salmonella, in fish harvested in waters containing untreated sewage. Important sources of bacterial contamination are unhygienic food-processing facilities, storage, cross-contamination, and inadequate worker hygiene
South African regulations applicable to microbiological safety of fish, processed fish and shellfish
Under the South African Foodstuffs, Cosmetics and Disinfectants Act, 1972 (Act 54 of 1972), the Regulations Governing Microbiological Standards for Foodstuffs and Related Matters, R. 692 of 1997, make provision for microbiological specifications for certain foodstuffs, and prescribe the following limits for microbial organisms in partly cooked, uncooked and cooked seawater and freshwater foods such as prawns, shrimps, crayfish, lobsters, crab meat, eels and fish.
Testing for microbiologicals
There are a number of microbiological tests for fish and fish products that can be used to check that microbiological status is satisfactory. The purpose of these tests may be divided into three different categories. They are performed in order to detect:
- pathogenic bacteria, of which certain bacteria cause food poisoning
- by infection in the gastrointestinal tract (Salmonella, E. coli, Vibrio spp), or
- by intoxication, where toxic metabolites (such as Histamine) are produced by the bacteria (Staphylococcus aureus,);
- indicator organisms of faecal pollution (faecal coliforms, faecal streptococci);
- other types of general contamination or poor handling practices (coliform bacteria,faecal streptococci, total viable count).
Estimation of bacterial numbers in fish is frequently used to assess microbiological quality retrospectively, or to assess the presumptive safety of the product; but the number, size and nature of the samples greatly influence the results, and even the most elaborate sampling cannot guarantee the safety of the product [2].
Heavy Metals in Fish, Processed Fish and Shellfish
Fish have been shown to contain varying amounts of heavy metals, of which mercury is the most common. Mercury is often concentrated in fish and shellfish in the form of methylmercury, a highly toxic organic compound of mercury. Bio-accumulation of mercury in seafood can carry over into human populations, and potentially result in mercury poisoning. Mercury in fish is a potential health concern for women who are or may become pregnant, nursing mothers, and young children [3]. High exposure to mercury has been found to induce changes in the central nervous system, potentially resulting in irritability, fatigue, behavioural changes, tremors, headaches, hearing and cognitive loss, dysarthria, incoordination, hallucinations, and death. It has been indicated that even exposure to low doses of mercury affects endothelial and cardiovascular function [5].
Higher concentrations of mercury are found in species of fish that are long-lived and high on the food chain, such as marlin, tuna, shark, swordfish, king mackerel, tilefish and northern pike [4].
Figure 1: Mercury-containing plants and tiny animals are eaten by smaller fish that are then eaten by larger fish, whose tissues accumulate mercury. That is why larger, longer-living predators such as sharks and swordfish tend to have more of the toxin than smaller fish such as sardines, sole, and trout [3].
Other metals may also be present in toxic quantities and have a detrimental effect on general health, which means it is important to monitor metal concentration in fish meat and to ensure compliance with food safety regulations; and consequently, to protect consumers [6].
South African regulations applicable to metal levels in fish
Regulations relating to the maximum levels for metal in foodstuffs (R. 500, 2004 as amended) specify maximum levels in fish and processed fish for arsenic, cadmium, lead and mercury; and in shellfish and shellfish products, maximum levels are set for cadmium and mercury.
References
[1] Charles Feng, Suzanne Teuber, M. Eric Gershwin: Histamine (scombroid) fish poisoning: a comprehensive review. Clinic Rev Allerg Immunol; Published online: 27 January 2015. [2] FAO: Chapter 5 – Fish Quality Assurance: http://www.fao.org/docrep/x5624E/x5624e08.htm: (retrieved 30 May 2016) [3] Langtree, I. Mercury Levels in Fish: Chart & Information (2015). [4] U.S. Food and Drug Administration. Mercury Levels in Commercial Fish and Shellfish (1990-2010). Accessed May 2016. [5] Azevedo et al. (2012). Toxic effects of mercury on the cardiovascular and central nervous systems. Journal of Biomedicine and Biotechnology. Volume 2012, Article ID 949048, 11 pages. [6] Bosch et al. (2016). Heavy metals in marine fish meat and consumer health: a review. Journal of the Science of Food and Agriculture, 96: 32-48.