The term restructured has the general meaning of binding smaller pieces of meat together to generally give the impression that a larger meat cut has been created that can produce slices of desired size for sandwiches or steak for plating at dinner. Processors have used various technologies to restructure ham since the 1950s. Mixing pieces of meat with ingredients, but especially appropriate levels of salt and alkaline phosphates, results in the osmotic movement of the ingredients throughout the meat particles and the extraction of myofibrillar proteins. The extracted myofibrillar proteins within the particles and on the surfaces of the particles form a heat set gel when the products are cooked. This gel is a very effective binder of water and fat and results in the binding of the meat pieces together and the retention of water and fat during cooking. This basic reaction is the primary system for the production of the very popular lunch meat types such as ham, turkey, and sliced beef. These products may be prepared from whole muscles or pieces of muscles or combinations of the two. The essential ingredients of salt and alkaline phosphates are added in a pickle that is usually injected into the meat pieces with large multineedle injectors. Sometimes the particles are slashed at frequent intervals to increase the surface area for protein extraction. This is called maceration or tenderizing. To further enhance protein extraction, the injected meat pieces are subjected to mechanical action in mixers, blenders, massagers, or tumblers. Portions of the mixture are then placed in appropriate casings or forms to create the final product shape and size. Often the shape of the final product is devised to mimic the whole muscle counterpart such as a ham, a beef roast, or a turkey breast. Cooking sets the protein gel, and the product can be uniformly sliced to create slices free of visible fat and connective tissue. Key references in this area are Pearson and Dutson (6) and Franklin and Cross (7).
Although the salt/phosphate-based binding system has obtained very widespread application, it has several limitations. Products must be marketed either precooked or frozen as the material will not cohere in the uncooked refrigerated state. Salt discolors the raw meat and accelerates oxidative rancidity. In recent years, several systems have been developed to bind meat without cooking to make products that look like whole tissue meats. The products can be marketed raw and have enhanced flavor and color stability. The five cold binding systems to be discussed are based on alginate/calcium, fibrinogen/thrombin, surimi, transglutaminase, or egg/milk/soy proteins. Although restructuring systems make comminuted meat appear to be an intact cut of meat, the restructured steak or roast has bacteria distributed throughout the interior of the product that is different from an unprocessed intact steak or roast. Therefore, it is imperative the restructured product be stored and, especially, cooked properly. Otherwise, food safety concerns for restructured products are the same as for any other comminuted meat.
Alginate forms a chemical bond with calcium ions to form a cold-set but heat-stable gel. High guluronic acid alginate is mixed with meat, and then a moderately slow release calcium source such as calcium carbonate or encapsulated calcium lactate is added along with an acidu-lant such as glucono-d-lactone. After the ingredients are mixed with the meat pieces, the product is formed and chilled for a day to permit the chemical binding to continue to form (8).
Fibrinogen/thrombin binding system is based on the mechanism used to clot blood (9). The materials are usually prepared from beef blood collected in a sanitary manner. Approximately 5% of a fibrinogen/thrombin mixture is added to meat pieces to be bound together, mixed, and formed into the final desired shape. Once all the materials are mixed, it is important to quickly form the product and let it set for about 12 h. The time to gel is fairly rapid, and the process must be done in relatively small batches to avoid forming delays. In addition, the materials are natural, biological materials obtained from beef cattle during the slaughtering process. Special care must be taken to minimize microbial contamination and growth during binder preparation, storage, and utilization.
Surimi is a wet concentrate of the proteins of fish muscle produced by water washing of minced fish. Cryoprotec-tants such as 4% sucrose and 4% sorbitol permit surimi to be stored frozen for more than a year with little loss of gel forming ability (10). Research has shown surimi can be used in red meats as a cold binding system. There has been no commercial application of this process, probably due to flavor effects.
Transglutaminase is an enzyme that catalyzes the formation of a chemical cross-link between peptides containing glutamine and lysine. Transglutaminase can be used to increase the gelation capacity, physical strength, viscosity, thermal stability, and binding capacity of protein foods. A commercial binder based on this enzyme is used at the 1% level to bind meat, poultry, and fish pieces. This is a fast gelling binder and must be used in a batch system to mix and form in 30 min or less and sit for at least 2 h to gel. It is used in conjunction with sodium caseinate, sugar fatty acid ester, and dextrin or with sodium polyphosphate, sodium pyrophosphate, sodium ascorbate, and lactose (Aji-nomoto U.S.A., Inc. Teaneck, NJ).
A commercial blend of proteins is sold as a cold-setting meat binder. The blend called PEARL MEAT contains egg white, casein, lactalbumin, gelatin, hydrolytic egg white extractive, hydrolytic casein extractive, soybean protein, and hydrolytic flour protein extractive. The meat is coated with the powder and quickly pressed and formed as the binding will be completed in 30 min (Chiba Flour Milling Company, LTD. Japan).
All of the binding systems require that the particles of meat being bound together be naturally tender, lean, have good color and flavor, and react well during subsequent cooking. Also, as mentioned earlier, the surfaces of the meat pieces that are subsequently bound on the inside of a restructured roast or steak must be assumed to contain some pathogenic bacteria such as Salmonella. Thus, restructured meats must be cooked sufficiently to kill these bacteria present in the center of the restructured cut. Thus, many of the cold binding systems are limited by the quality and cost of the raw materials and the need for more extensive cooking than intact cuts.
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