Nowadays, seafood plays a very important role in human nutrition worldwide. It is among the major foods consumed globally, mainly due to a large movement towards healthier eating. International trade in seafood and new seafood products is growing rapidly and there are more and more reports of adverse reactions in the population consuming seafood. The generic term “crustaceans” includes all arthropodic aquatic animals, with six major subgroups and 44,000 species. Hidden crustacean proteins in food represent a critical problem for people with crustacean allergies. Sufferers have to avoid the consumption of food containing crustaceans very strictly. Still, cross-contamination can occur as a consequence of the production process.
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International organizations, such as the Codex Alimentarius Commission of the World Health Organization, or WHO, and the Food and Agriculture Organization, or FAO, have discussed a labeling system for allergenic ingredients in processed food and labeling is now recommended for eight food groups, including crustaceans. In the European Union, there are different regulations that establish labeling must be present in regards to the main types of food allergens to warn consumers. In the U.S., the Food Allergen Labeling and Consumer Protection Act of 2004 includes the eight major allergen groups—namely milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, and soybeans. However, allergens can be present in the final food product even though the ingredients are not allergens due to cross-contamination between raw materials, equipment, or production lines. Therefore, there is increasing need for sensitive detection of crustacean residues in foodstuffs, as well as diagnosis and treatment of seafood allergies to protect the allergic consumer and to ensure supervision of labeling requirements by the authorities responsible.
Food allergies in general have become an important health problem and represent a food safety issue. Food allergies, defined as an adverse immune response to food proteins that the human body mistakenly identifies as harmful, affect approximately 5 to 8 percent of children and 2 to 3 percent of adults in developed countries, with rising prevalence. A true allergic reaction is defined as a type-one hypersensitivity activating a specific type of white blood cells, the mast cells, leading to an immunoglobulin E response. Histamine and inflammatory mediators, such as cytokines, are released, leading to different symptoms, including itchiness, gastrointestinal disorders, dyspnea, or even anaphylaxis and death.
Crustaceans are among the eight food groups thought to lead to allergies triggered by immunoglobulin E antibodies worldwide. Hypersensitivity reactions to different ingested crustaceans, including shrimps, crabs, lobsters, and others are among the most frequent causes of food allergic reactions. Furthermore, crustaceans are the third most important foodstuffs inducing food-related anaphylaxis. Several studies have shown that even minute amounts of ingested seafood allergens can trigger very quick allergic reactions. It is assumed that even inhaled airborne allergens can lead to sensitization and allergic reactions. Very commonly, crustacean allergies appear at later stages of life and the likeliness of them being outgrown, as it is very often the case in childhood allergies, is very small.
The major allergen in shrimps and other crustaceans is the ubiquitous muscle protein tropomyosin, which is responsible for ingestion-related allergic reactions. It is a highly conserved protein, is homologous in different species, and shows a considerable rate of identicalness. Its high cross-reactivity even to insects like house dust mites means tropomyosin is considered as a possible cause of cross-reactivity between food and respiratory allergens of animal origins. There are other allergens that have been identified in crustaceans in the past few years, including arginine kinase and myosin, but they have not yet been characterized completely. In contrast to other seafood allergens, tropomyosin seems to be relatively resistant to acidic digestion and heat. The heat stability makes this protein suitable for the analysis of crustacean residues in processed food samples. Therefore, allergen-specific detection assays in food products are available for crustacean tropomyosin.
The detection methods for food allergens, including crustacean protein, have to be very specific and must detect minute quantities of allergen in very complex food matrices. At present, there are qualitative and quantitative test methods for crustacean residues available. Few techniques detecting crustacean protein, actually tropomyosin, are available, including immunological methods based on a specific antigen-antibody reaction, such as lateral flow assays and enzyme-linked immunosorbent assays (ELISA), as well as DNA-based methods such as polymerase-chain reaction (PCR) technologies, mainly real-time PCR.