Casein is manufactured by adding acid to warm skim milk. As the pH of the skim milk lowers to the range of 4.2 to 4.6, the casein precipitates out of the skim milk as a curd. The casein curd is then washed repeatedly with acidified fresh water to “purify” the casein (wash away unwanted, occluded milk solids such as fat and lactose). Because the casein curd is kept at an acid pH, the milk minerals are leached out of the protein. The result is a relatively pure protein curd (96% protein on a dry basis).
This casein curd, however, is not very useful in food products. Acid casein (as the curd is known) is insoluble in water, behaving much like sand. In order to make the casein curd more useful in food products, the acid casein curd is reacted with a strong alkali to result in an almost neutral protein product termed a caseinate. The type of alkali used to neutralize the acid casein curd will determine what type of caseinate is produced. For example, reacting acid casein curd with sodium hydroxide (to a pH of about 6.8) results in the formation of sodium caseinate. Reacting acid casein curd with calcium oxide or calcium hydroxide (to pH 6.8 to 7.6) results in the formation of calcium caseinate. Sodium caseinate is the most water soluble form of caseinate. Sodium caseinate typically forms high viscosity water dispersions, has an amber color in water, and imparts a “glue-like” sodium flavor. Sodium caseinate is the basis of simple glues. Calcium caseinate forms a low viscosity, opaque, off white dispersion in water. Calcium caseinate is usually the least water soluble of the caseinates and tends to sediment out of suspension within hours of being mixed into water. Whereas sodium caseinate will exhibit a smooth mouthfeel when dispersed in water, calcium caseinate will exhibit a slightly gritty or grainy mouthfeel. There are also sodium calcium caseinates, calcium sodium caseinates, and even calcium ammonium caseinates. The levels of each mineral are determined by the ratios of alkali used in the caseinate manufacture. The higher the sodium content, the higher the viscosity and water solubility. The higher the calcium content, the lower the water viscosity and solubility. Potassium caseinate possesses properties similar to sodium caseinate and magnesium caseinate possesses properties similar to calcium caseinate.
The process of manufacturing acid casein and/or caseinates does extensive damage to the proteins. Some of the “damage” causes off flavors to develop. Dried acid casein, for example has a very strong, objectionable odor and flavor that is difficult to cover up. Although much work is performed to decrease or eliminate these objectionable casein flavors when manufacturing caseinates, most people would agree that caseinates still possess strong objectionable flavors – usually these flavors are described as “cow-ey”, “barny”, “gluey”, and “livestock”.
Milk Protein Concentrate and Isolate, on the other hand, is manufactured by a gentle process. At Idaho Milk Products, our MPC/MPI is manufactured at cold temperatures. We do not add chemicals* to the milk and the milk does not undergo pH changes. The milk protein is separated out of skim milk using filtration techniques. MPC/MPI typically contains high levels of milk calcium, phosphorous, potassium, and magnesium. These minerals are bound to the protein. Milk protein concentrate and isolate typically have no odor and a very bland flavor profile. Milk protein concentrate and isolate typically contain about 80% casein and 20% whey proteins. These proteins are present in MPC/MPI in the natural (Native), undamaged (undenatured) state.