By Prof. John Abiodun Daramola
Overview of finfish, shellfish and contamination
Fish and shellfish are very important proteinous portion of the human diet worldwide. They come in extremely varied food products with numerous fish species, from marine and freshwater, from cold temperate and warm tropical waters, farmed or wild and processed or preserved in different ways. The above variations affect the microbiology of the fish, shelf life and safety.
Proper handling of fish between capture and delivery to the consumer is a crucial element in assuring final product quality. Also the standards of sanitation, method of handling, the time and temperature of holding fish are all significant quality factors. With a few exceptions, freshly caught fish are considered free of pathogenic bacteria of public health significance. The presence of bacteria harmful to man generally indicates poor sanitation in handling, processing and the contamination is almost always of human or animal origin.
On the other hand, food is considered to be microbiologically unsafe owing to the presence of microorganisms which may invade human body (e.g Salmonella, Escherichia coli, Listeria monocytogenes, etc) and also those that produce toxins ingested with a food such as Staphylococcus aureus, Clostridium botulinum and Bacilus cereus (Ofred, 2009). A number of microbiological tests of fish and fish products are used by authorities to check that the microbiological status is satisfactory. The purpose of these tests is to detect pathogenic bacteria or indicator organisms of faecal pollution such as Escherichia coli or other types of general contamination or poor handling practises (coliform bacteria, faecal streptococci, total viable count). However, microbiological testing can be costly and time consuming.
The microbiology of fish and fish products is complex and covers a wide range of both quality and safety related issues. When fish are alive, the muscle tissue is considered to be sterile, but after death, the barriers to microbiological invasion begin to break down and bacteria are able to grow more freely, although will be rarely found within deep muscle tissue. After the fish is caught and dead, the microflora may begin to change due to the varying environmental conditions.
Meanwhile, the term fish processing refers to the processes associated with fish and fish products between the time fish are caught or harvested and the final product delivered to the customer. The central concern of fish processing is to prevent fish from deteriorating and this should remain the underlying factor. Fish processing can be subdivided into fish handling-which is the preliminary processing of raw fish and the manufacture of fish products. Another natural subdivision is the primary processing level involved in the filleting and freezing of fresh fish for onward distribution of fresh fish and the secondary processing that produces chilled, frozen and canned products for the retail and catering outlets. Canned fish are fish which have been processed, sealed in an airtight container such as a sealed tin can and subjected to heat. Fish products are preserved using almost every food processing technique that has ever been developed (drying, smoking, freezing, canning, fermenting, high pressure processing) and of course, there is the increasing trend towards the consumption of high quality raw fish in the form of sushi.
Procedures for ensuring fish and seafood safety
The same rules about food safety and preparation apply to fish as with any other food products. If fish is left out on a work surface for any period of time, then it will decay or “go off” very quickly. Raw and cooked fish must not come into contact with each other due to the risk of cross contamination. This means using separate utensils and chopping boards for raw and cooked fish and wiping them down after use. Fish needs to be cooked thoroughly and at the correct temperature. One exception to this is sushi. The sushi is a popular Japanese dish which consists of raw fish, e.g. salmon, rolled in rice and seaweed. It is available in restaurants and as ready prepared packs in supermarkets. Generally, this is safe to eat as long as the fish used has been cooked or if raw, has been frozen beforehand in order to kill off any parasites.
Despite the wide range of canned fishery products that are available, there are relatively few operations which are unique. The correct pre-process handling techniques and refrigerated storage conditions of all fish for canning have much in common (in fact, there is very little difference in the handling methods of fresh fish and processed fish). Similarly, with the seaming, with retort operating procedures and post-process handling of containers, the methods adopted are independent of the type of the product. The purpose of retorting-that is to achieve a shelf-stable and safe product by the application of lethal heat remains the same for all canned fishery products. It is understandable that there are common guidelines which discourage manual handling of all processed wet containers and recommend that all retort cooling water be chlorinated.
There is a direct and unavoidable relationship linking raw material quality and end product quality and this holds as much for the production of canned fish as it does for fish which is bought fresh and prepared at home. Because handling conditions immediately after catching are responsible for rapid loss of the “fresh” quality, the quality of canned fish suffers whenever the raw material is temperature abused or physically damaged between catching and thermal processing. This means that the quality criteria considered desirable by cannery management when they assess their raw materials ought to be the same as those chosen by consumers when they purchase fresh fish. Fish for canning can be trimmed to remove bruises and other localised flesh defects. As the quality of fish deteriorates from the moment of death, all that can be hoped for by good handling is to retard the rate at which undesirable, quality degrading, changes occur.
All of the pre-treatments ought to be carried out under conditions of good manufacturing practise, which means that the rudimentary steps of process hygiene should be implemented. Satisfactory control of contamination from operating surfaces and raw materials is achievable with regular cleaning (i.e., by washing the product, cleaning the line and ancillary equipment) and limiting the duration of exposure at temperatures suitable for growth of spoilage microorganisms.
In summary, seafood safety tips involve carefully buying from a reputable seller, keep seafood cold and live shellfish alive, refrigerate live shellfish properly, do not cross-contaminate and cook seafood thoroughly (Schmutz et al., 2020).
Professor John Abiodun Daramola is the HOD, Department of Agriculture and Agricultural Technology as well as the Director, Centre for Agricultural Technology and Entrepreneurial Studies (CATES) Bells University of Technology, Ota, Ogun State, Nigeria