Emulsifying agents (melting salts) are of major importance in processed cheese production. They provide a uniform structure during the melting process and affect the chemical, physical, and microbial quality of the product. Emulsifying agents are not emulsifiers in true chemical sense; that is, they are not surface-active compounds, although they help in emulsifying fat and stabilizing the emulsion. True emulsifiers like mono- and diglycerides may be included in commercially produced emulsifying agents, which are mixtures of selected compounds. The most com-
mon components of the commercial salt mixtures are phosphates, polyphosphates, and citrates (Table 4), although compounds such as sodium potassium tartrate, complex sodium aluminum phosphate, sodium potassium tartrate, trihydroxyglutaric acid, and diglycolic acid could be used as well. The mixtures are of a constant and guaranteed quality; their composition is a secret and protected by the producer. The world's best-known commercial emulsifying agents producers both came from Germany: Benckiser-Knapsack, GmbH (Joha salts) and Giulini Chemie, and GmbH (Solva salts), which recently fused together in a single company entitled B. K. Giulini Chemie, in Ladenburg. Smaller producers come from a few other countries, such as Yugoslavia (KSS emulsifying salts, produced by Kotek-
sprodukt) and the Czechoslovakia Republic (CI-FO emulsifying salts). However, some huge food companies and processed cheese plants, like Kraft in the United States and Canada Packers in Canada, design and use their own emulsifying agents.
The essential role of the emulsifying agents in the manufacture of processed cheese is to supplement the emulsifying capability of cheese proteins and can be summarized as follows (4,5):
1. Removing calcium from protein system by sequestering
2. Peptizing, solubilizing, and dispersing the proteins
3. Hydrating and swelling the proteins
4. Emulsifying the fat and stabilizing the emulsion
5. Controlling pH and stabilizing it
The most important function of emulsifying agents is the ability to sequester calcium. Casein in cheese may be viewed as a molecule with a nonpolar, lipophilic end, whereas the other end, which contains calcium phosphate, is hydrophilic. Because of this structure, casein molecules function as emulsifiers (31). The solubility of casein in water, and hence its emulsifying capacity, are increased by reducing the calcium phosphate content. Calcium in the calcium paracaseinate complex of natural cheese is removed by the ion-exchange properties of melting salts, thus solubilizing the paracaseinate usually as sodium caseinate. Chemically, cheese processing could be observed as presented in Figure 5.
During processing, when higher temperatures are applied further polypeptide bonds are broken. Polyvalent anions of the emulsifying agents (eg, small ions of sodium diphosphate) attach themselves to the modified proteins, increasing their hydrophilic character. Protein molecules become larger, adsorb additional water, and thus increase the viscosity of the colloidal mass. This phenomenon is known as creaming. The affinity, that is, sequestering ability, of common emulsifiers for calcium increases in the following order: NaH2P04, Na2HP04, Na2H2P207, Na3HP207, Na4P207, Na5P3O10 (5). The affinity of protein
Table 4. Emulsifying Salts Used in the Processing of Cheese
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