FISH, SALTED. Sodium chloride (NaCl), also called salt, common salt, and table salt, is generally recognized as a safe (a status sometimes abbreviated by the acronym GRAS) antimicrobial and incidental food additive (Klaassen). Salt has been used for centuries as a seasoning and flavor enhancer as well as a preservative or curing agent. Salt has played a major role in many aspects of human life: nutritional, economic, political, and military. Egyptians preserved food by salting or sun-drying; Roman soldiers were paid in salt; Napoleon's campaign in Russia suffered a setback because of lack of salt; and salt was used in trade and exchanged for slaves in ancient Greece (Pszczola; Salt Institute). The Greeks also salted fish and used them as a part of their diet. Later, they passed this practice on to the Romans ( Jay).
Fish are highly perishable, and they will spoil rapidly if improperly handled. Fresh iced fish generally are spoiled by bacteria, but dried fish are usually spoiled by fungi (Jay). Salting as a method of preserving fish has been used for centuries and in many places around the world such as Asia, Europe, and Latin America. The simplicity of the salting process, the low cost of production and the ease with which it combines with other preservation methods, such as drying or smoking, has led to its popularity and extensive use (Berhimpon et al.).
In the usual process of dry-salting, whole fish are eviscerated, cleaned, washed, dry-salted, stacked in containers with more NaCl in between the pieces, stored for a salting or curing period, and then dried (using sunlight or artificial indoor drying chambers). The salting period depends on several factors including the desired ripened characteristics in fish, the fish species, the amount of salt used, and the storage temperature. For example, increasing the amount of NaCl reduces the required time of storage.
Use of salt in fish preservation is not limited to dry application. Salt is an important additive in the preparation of fermented, pickled, or processed fish or fish products. In the making of fermented fish, known concentrations of salt are added to promote degradation of proteins and retard the growth of undesirable, putrefactive microorganisms. Also, this allows desirable, NaCl-tolerant (halotolerant), fermentative species such as lactic acid bacteria to grow. Pickled fish are marinated in salt brine or brine containing vinegar. Curing salt (containing sodium nitrate, NO3) can be added to the pickle to delay spoilage and control microbial activity during storage (Pederson and Meyland). Other ingredients—spices, sugar, herbs, or vinegar—are incorporated during the process to impart a particular flavor, texture, or color. Herring, haddock, and anchovies are fish species often available in the market in pickled form.
In manufacturing processed fish products, adding certain amounts of NaCl assists in the extraction of salt-soluble proteins and the formation of a sticky paste of fish meat. The development of the gelled paste might be due to the formation of a protein network structure or polymerization of myosin-heavy chains (Kumazawa, Numazawa, Seguro, and Motoki). In breaded processed fish products, NaCl is used in the predusting step to enhance adhesion of the batter to the fish (Claus, Jhung-Won, and Flick). Processing fish has created a niche market for products that otherwise would have been wasted because of overharvesting of species, low consumer appeal, high processing costs, or limited shelf life.
Salt, Spoilage, and Preservation
Over the years, a number of spoilage and pathogenic microorganisms, including lactic acid bacteria, Pseudomonas spp., Staphylococcus spp., Salmonella spp., Clostridium perfringens, Clostridium botulinum, Escherichia coli O157:H7, and Listeria monocytogenes, have been associated with fish and fish products. At certain concentrations, salt was found to prevent growth of many microorganisms by exerting a drying effect on microbial cells and tissue, which concentrates solutes in them, creating an environment unsuitable for microbial proliferation. Because some halotolerant or halophilic (salt-loving) microorganisms are not affected by salt, additional treatments such as drying, heating, curing, or smoking are helpful in controlling them. Dry-salted fish (that is, dried by the salting method), for example, are dried and/or smoked to extend their shelf life.
In addition to microbial spoilage, fish that contains high levels of lipids—salmon, herrings, and mackerel—are prone to oxidation and become rancid as microbial spoilage occurs ( Jay). Because of their unsaturated nature, fish body oils are susceptible to oxidation and also easily develop rancid and unacceptable odors and flavors during storage (Waterman). Once fatty compounds are oxidized, the breakdown products of lipid oxidation potentially can react with proteins and vitamins, leading to a loss of nutritional value and quality of the fish (Pokorny). Salted sun-dried fish are more prone to oxidation than fish preserved by other methods because of their exposure to light and oxygen (Smith and Hole). Use of crude NaCl (which contains impurities such as chlorides, sulfates, calcium, and heavy metals) accelerates lipid oxidation during fish processing and will adversely affect the overall quality of the finished product (Yankah et al.).
In order to reduce the adverse effects of NaCl on lipid oxidation, color, and flavor of fish, fish and fish products are handled, prepared, and processed under refrigerated temperatures. Low temperatures reduce the rates of oxidative reactions and retard microbial growth. Products also can be vacuum packaged after drying and/or cold or hot smoking. Vacuum packaging creates an environment that virtually lacks oxygen, a promoter of oxidative rancidity. Chelating agents, bio-preservatives, antioxidants, and other compounds also can be added to maintain color, flavor, and integrity of the products.
Throughout history NaCl has been a popular and important food additive. The many advantageous properties that NaCl possesses led to its incorporation in several unprocessed and processed foods. Its functionality as a preservative, catalyst in extraction of NaCl-soluble proteins (binder), flavor enhancer, and color developer has played a major role in food processing and preparation. Improvements and advancements in technology worldwide have allowed even better use of NaCl by the food industry, such as production of processed fish products. Because salt does have its limitations and disadvantages, its utilization conditions must be optimized to provide safe food for consumers, at the same time addressing their needs and concerns.
See also Fish; Fishing; Iodine; Meat, Salted; Military Rations; Preserving; Salt; Sodium.
Berhimpon, S., R. A. Souness, R. H. Driscoll, K. A. Buckle, and R. A. Edwards. "Salting Behavior of Yellowtail (Trachurus mccullochi Nichols )." Journal of Food Processing and Preservation 15 (1991): 101–114.
Claus, J. R., C. Jhung-Won, and G. J. Flick. "Processed Meats/Poultry/Seafood." In Muscle Foods: Meat, Poultry, and Seafood Technology, edited by D. M. Kinsman, A. W. Kotula, and B. C. Breidenstein. New York: Chapman and Hall, 1994.
Jay, J. M. Modern Food Microbiology. 4th ed. New York: Van Nostrand Reinhold, 1992.
Klaassen, C. D. "Principles of Toxicology." In Casarett and Doull's Toxicology: The Basic Science of Poisons, edited by C. D. Klaassen, M. O. Amdur, and J. A. Doull. New York: Macmillan, 1986.
Kumazawa, Y., T. Numazawa, K. Seguro, and M. Motoki. "Suppression of Surimi Gel Setting by Transglutaminase Inhibitors." Journal of Food Science 60 (1995): 715–717, 726.
Pederson, E., and I. Meyland. "Nitrate, Nitrite, and Volatile Nitrosamines in Pickled Fish Prepared with Addition of Nitrate." Zeitschrift für Lebensmitteluntersuchung und forschung A [European food research and technology] 173 (1981): 359–361.
Pokorny, J. "Browning from Lipid-Protein Interactions." Progress in Food and Nutrition Science 5 (1981): 421–428.
Pszczola, D. E. "Salty Developments in Food." Food Technology 51 (1997): 79–90.
Salt Institute. Facts about Salt. Alexandria, Va.: Salt Institute, 2000.
Smith, G., and M. Hole. "Browning of Salted Sun-Dried Fish." Journal of the Science of Food and Agriculture 51 (1991): 193–205.
Waterman, J. J. "The Production of Dried Fish." FAO [Food and Agriculture Organization] Fish Technical Paper, 160 (1976): 1–52.
Yankah, V. V., T. Ohshima, H. Ushio, T. Fujii, and C. Koizumi. "Study of the Differences between Two Salt Qualities on Microbiology, Lipid, and Water-Extractable Components of Momoni, a Ghanaian Fermented Fish Product." Journal of the Science of Food and Agriculture 71 (1996): 33–40.
James L. MarsdenMaha N. Hajmeer