Casein production - Use of separator and decanter in dairies
At a proportion of approximately 80 percent, casein is the most important protein fraction in cow‘s milk. Isolated casein is a valuable raw material for a wide variety of industrial sectors. The food industry uses casein in powdered form as high-quality protein. It also has great importance As a binder for paints, for gluing plywood, as a photoresist in etching and for the manufacture of adhesives, putty, textile finishes and block stains for leather.
Casein is present in milk in colloidal solution. Depending on temperature, casein particles have different sizes. Smaller particle sizes are described as casein submicelles, above that as casein micelles. Casein consists of long chains of molecules of different amino acids. These molecule chains are combined into submicelles which are held together by phosphate salts.
In order to isolate the casein, the casein micelles must be precipitated out of the milk. This becomes possible when the surface charge and consequently the repulsion forces of the casein molecules are reduced so that coagulation can take place. The alternative processes are called acid or rennet precipitation.
In acid precipitation using a mineral acid, the positively-charged hydrogen ions penetrate the casein micelles, as a result of which the negative net charge of the casein micelles drops. Simultaneously
the hydrate shell and the number of the doubly charged calcium ions are also reduced. The same-polarity charge and therefore the repulsion forces are reduced, so that the forces of attraction predominate. The heat energy of the particles causes them to collide and unite into larger aggregates which then precipitate out of the milk.
Unlike acid precipitation, which is reversible, in rennet precipitation, micelle components are irreversibly cleaved off. The rennet enzyme cleaves the calcium-insensitive hydrophilic part. Around 50 percent of the net negative charge of the casein surface is thus lost, weakening the protective hydrate shell and exposing the calcium-sensitive part of the casein on the surface of the micelle. Aggregation now takes place in the second coagulation phase following the enzymatic reaction. The actual gelation takes place by bridging the aggregates with calcium ions.
Bacteria removal from the skimmed milk
Whether using rennet or acid precipitation, a well degreased skimmed milk is the starting point for producing casein. In order to be able to manufacture a perfect end product, the skimmed milk not only has to be pasteurized but also as free of germs as possible. In the bacteria removing separator, the bacteria and germs are centrifugally separated and discharged from the bowl by partial ejection. The bacterially clarified skimmed milk is subsequently heated to coagulation temperature in a plate heat exchanger.
Casein recovery from whey
Depending on the casein type (acid or rennet), the casein is precipitated either by inline addition of technical acid or by the use of enzymes with the addition of rennet. The latter method of precipitation requires a certain amount of time and is therefore carried out in batch. To support and promote the coagulation process, further indirect temperature treatments with subsequent reaction stages follow. Actual separation of the coagulated casein from the whey is performed by decanters. The whey which forms is cooled, clarified and then passed on for further processing. In order to increase the degree of purity of the raw casein, it needs to be largely freed from the minerals and lactose adhering to it. To achieve this, it is washed several times on the countercurrent principle and is then dried to a residual water content of maximum 10 percent.