Phosphate Functionality in Dairy Applications
In dairy applications, phosphates are used for a number of functions. Phosphates stabilize milk proteins against coagulation from extreme heat, pH or sheer; buffer products within the desired pH range; support emulsification by interacting with proteins; and bind calcium in milk gels. Nutritionally, phosphates can help fortify with calcium, magnesium or potassium. Phosphates sequester metal ions and also have bacteriostatic effects. Many of the applications in processing of dairy products involve interactions between phosphates and casein, or the calcium in the casein micelles.
Phosphates start with phosphoric acid; when combined with alkali metals, such as sodium, potassium, calcium or magnesium, an ortho-phosphate salt will form. Upon heating, ortho-phosphates combine to form chains, first pyro-2, then tripoly -3, and then longer chains known as polyphosphates or hexametaphosphate–with a chain length from 4 - 28 or greater.
Orthophosphates, most commonly disodium phosphate (DSP) or dipotassium phosphate (DKP), function as buffering agents, controlling and maintaining optimum pH to assure milk protein stability. Phosphates reduce protein denaturation and casein aggregation.
“Lactose degradation and organic acid formation upon heating cause the pH to fall,” advised Amanda Benenati, research associate, at Innophos, in her Prepared Foods’ R&D Seminar presentation “Phosphate Functionality in Dairy Applications. “
Polyphosphates such as sodium hexametaphosphate (SHMP) are linear chains, which peptize proteins, sequester minerals and have bacteriostatic effects. Through selection of the correct phosphate, melting and texture of cheese and sauces can be controlled. Selection of the correct SHMP is important for the best peptization rate. Peptization is the reverse process of coagulation. It increases the solubility and dispersion of proteins. Increasing the chain length and concentrations of SHMP provide better peptization rate. Long-chain SHMP decreases melt and does not provide the long texture required for good slicing properties.
Pyrophosphates contribute to emulsion stability and help the mixture thicken (creaming reaction). “This thickening is a clear sign of reformation of the modified protein matrix,” explained Benenati. During the creaming reaction, anionic phosphates interact with positive charges on casein proteins, unfolding the proteins and allowing them to behave as emulsifiers. As pH increases, greater fat emulsification is possible, along with spread or melt.
When selecting an emulsifying salt for process cheese, age and moisture content of the starting cheese should be considered, along with the amount of rework in the formula and manufacturing conditions.
“Generally, blends of more than one phosphate are used to control firmness and emulsification. Typical pH range in process cheese is from 5.5-6.0. At higher pH, firmness increases. Outside of the target pH range, higher or lower, both texture and flavor suffer. In process cheese, pH can alter protein solubility and configuration, as well as the ability of emulsifying salts to bind calcium,” added Benenati.
Phosphates are used in many different dairy-based products. In fluid milk, DSP or DKP stabilizes casein during heat treatment, preventing coagulation. SHMP adds shelflife to milk by preventing age gelation, while tetrasodium pyrophosphate (TSPP) enhances the viscosity of chocolate milk by forming a weak calcium pyrophosphate gel. This gel interacts with casein to provide viscosity and appears to improve color.
Blends of orthophosphates and polyphosphates are essential in protein stabilization of dairy products during pasteurization, HTST, and UHT for beverages and sauces. Pyrophosphates contribute improved whipping properties and reduced syneresis in whipped cream. In pudding and instant cheesecakes, phosphates promote gel formation. DKP and DSP are key to stabilization of dairy- and non-dairy-based coffee creamers, especially when they are added to hot, acidic coffee.
“Phosphate Functionality in Dairy Applications,” Amanda Benenati, research associate, Innophos, 609-366-1373, Amanda.benenati@innophos.com
—Summary by Elizabeth Pelofske, Contributing Editor
Originally appeared in the April, 2016 issue of Prepared Foods as Developing for Dairy.
