“Phosphates are ubiquitous in the food industry, but nowhere is their importance greater than in meat and poultry systems,” says Jim Anderson, business development manager-Americas, ICL Food Specialties, St. Louis. “Their functionality remains unique in the world of food ingredients.
“Their primary role in meat systems is best described as ‘protein management,’” he explains.
When protein is in its isoelectric point, which is at about pH 5.1, it does not bind water very well. However, when meat protein is charged, it attracts water and binds it. Protein gets charged by lowering or raising its pH. That’s one of the functions of phosphates.
“After animals are harvested, the energy source adenosine triphosphate depletes. This changes the protein,” says Peng Yuan, scientist and manager-application and product development, Innophos Inc., Cranbury, NJ. “First, the muscle pH drops due to the accumulation of lactic acid from anaerobic respiration and then the muscle stiffens as rigor mortis sets in. Alkaline phosphates can increase the pH of muscle, thus moving it away from the protein isoelectric point, that point where the muscle has lowest water-holding capacity.
“Some phosphates, specifically pyrophosphates, can also tenderize the stiffened muscle fibers and increase water binding sites by disassociating actomyosin,” Yuan says. “The key functions are pH modification and protein modification.”
Food-grade phosphates are derived from phosphoric acid and can assume many forms. Most are linear molecules and contain a single phosphate (ortho), two phosphates (pyro) or three or more phosphates (poly). There are also metaphosphates, which are composed of several phosphates in a ring-shape structure. Most phosphates are alkaline and have a high pH; however, there are some phosphates referred to as acid phosphates, and they have a neutral to slightly acidic pH.
Suppliers typically offer proprietary blends with unique functionalities for specific applications. When used with sodium chloride, the ingredient system further increases the water-holding capacity of the protein.
Phosphates also chelate ions in the protein system, which contributes to increased water-holding capacity. Chelating divalent ions prevents them from forming cross-bridges between proteins, allowing the proteins to more readily unfold and bind free water.
“Iron is widely found in hemoglobin from blood cells and in myoglobin from muscle cells,” adds Yuan. “When meat is cooked, iron will be partially released from hemoglobin and myoglobin, which in turn will facilitate lipid oxidation in final products. Pyro and polyphosphates have been proven to be excellent chelators of iron. Binding the iron delays the development of rancidity in processed meat.
“The buffering capacity of phosphates decreases as chain length increases,” Yuan says. “Only pyro and higher-order phosphates have chelation capacity, and this varies by mineral and pH.”
From a USDA labeling perspective, phosphates need only be declared as “sodium phosphate,” or in the case of the new generation of no-sodium phosphates, then “potassium phosphate.” “But in actuality, each is unique in character and performance,” Anderson says. “Buffering capacity, chelation, water-holding capacity and solubility vary greatly, depending upon the chain-length of the respective phosphate.”
Functional and economic benefits
Proper selection and use of phosphates can increase yields by more than 10 percent, thus reducing shrinkage (moisture loss) and purge (cook-out) during further processing and final cooking. This has both economic and product quality advantages.
“Superior cook yields cannot be over emphasized, especially when quality is considered,” Anderson adds. “And while these attributes are critical in today’s marketplace, phosphates also provide ancillary benefits. These include color development and stabilization, flavor protection from oxidation and antimicrobial properties, to name a few.”
Yuan explains how phosphates improve the eating quality of meat. “For example, phosphates can increase the cooking yield and shelf-life of processed meats while maintaining juiciness and flavor,” he says. “They improve stability of emulsion products, such as hot dogs, and reduce purge after vacuum packaging. In frozen products, phosphates diminish freeze-thaw loss and in formed products, they bind meat chunks together.
“When acidic phosphate is used in the curing process, phosphates shorten the curing process,” he adds. “Cured meat develops color due to the binding of myoglobin with nitric oxide. Decreasing the pH by 0.2 to 0.3 units will double the production rate of nitric oxide and in turn, cured color. Acidic phosphates, such as sodium acid pyrophosphate facilitate the production of nitric oxide.”
Phosphates added to uncooked frozen poultry products exert a cryoprotective effect on the protein and lipids. This assists the protein with binding water and minimizes moisture loss during thawing while also protecting against the development of rancid flavors.
In the production of comminuted poultry, such as chicken nuggets and turkey franks, phosphates, salt and ice are added to the ground meat and physically mixed for dispersion. The hydrated protein forms a matrix that entraps the fat, with the phosphate stabilizing the emulsion during the cooking process. This results in decreased cook-cool loss.
Like other ingredient technologies, phosphate offerings continue to improve. “Innovations have focused on several key attributes, including development of phosphates with varied chain lengths, targeted pH range, mixed sodium and potassium content, controlled crystal structure, improved rate of dissolution, salt tolerance and innovative chemical blends for optimal performance,” Yuan says.
Phosphate selection is application specific. Considerations include the raw-muscle protein, other ingredients, water source, processing and the final product’s target composition.
“Only then can the proper phosphate solution be selected with confidence,” Anderson says. “This comprehensive approach to phosphate product selection also ensures that the absolute best protein management has been achieved, resulting in increased yield and quality maximization.”
As previously mentioned, other ingredients and the water added to the meat system must be considered, as high levels of certain minerals, in particular calcium, iron and magnesium, can negatively impact the phosphates ability to increase the water-holding capacity of the proteins.
Method of phosphate addition is another consideration, as phosphates tend to be less soluble than other ingredients. If not properly dissolved, issues can arise in injection processes. In tumbled systems, undissolved phosphates will not be properly absorbed by the protein.
If labeling restrictions prevent the use of phosphates, dried plums are a natural alternative. According to the California Dried Plum Board, Sacramento, dried plum mixtures can substitute for phosphates in various poultry applications. This is because dried plums have a high level of inherent sorbitol, a sugar alcohol that is an effective humectant for binding and holding moisture. Dried plums are also a source of fiber, which further contributes to moisture binding and holding. And, dried plums contain malic acid, a natural flavor potentiator to round out and enhance savory flavors.
It’s all about binding water and delivering a succulent meat product. Taste reigns.