Casein coagulation

On acidification to pH 4.6, the caseins coagulate, which is the principle used to manufacture of a family of cheeses which represent about 25% of total cheese consumption and are the principal cheeses in some countries (Appendix 10B). Acidification is traditionally and usually achieved by in situ fermentation of lactose by a Lactococcus starter but direct acidification by acid or acidogen (gluconic acid-d-lactone) is also practised. The principal... 

To increase curd elasticity and improve eye formation, the milk used to produce Swiss cheese must be clarified. Standardization of the fat content of the milk after clarification ensures uniform composition. Rennet and lactic acid from the bacteria cause casein coagulation. Swiss cheeses made in the United States are cured for three to four... 

Helesicova, H. and Podrazky, V. 1980. Casein coagulation by hydrochloric acid. Prumysl. Potravin (Czechoslovakia) 31, 210-213 (Czechoslovakian). 

Casein coagulation characteristic flavors during aging... 

Manufacture. The natural zymotechnics process (lactic acid fermentation) When lactic acid is formed in milk by the action of lactic acid bacilli, the casein coagulates due to the acidity of the lactic acid. There are several other methods. 

Cheese Casein coagulation. Characteristic flavor development during aging. 

Vitamin A (845 RE/L) and vitamin D (913 RE/L) may be added to fortify evaporated milk. Other possible ingredients are sodium citrate, disodium phosphate, and salts of carrageenan. Phosphate ions maintain an appropriate salt balance to prevent coagulation of the protein (casein) during sterilization. The amount of phosphate added depends on the amount of calcium and magnesium present. 

At the pH = Jt there is a balance of charge and there is no migration in an electric field. This is referred to as the isoelectric point and is determined by the relative dissociation constants of the acidic and basic side groups and does not necessarily correspond to neutrality on the pH scale. The isoelectric point for casein is about pH = 4.6 and at this point colloidal stability is at a minimum. This fact is utilised in the acid coagulation techniques for separating casein from skimmed milk. 

Destruction of the casein micelles in the milk with subsequent precipitation of the casein can be accomplished in a number of ways. The action of heat or the action of alcohols, acids, salts and the enzyme rennet all bring about precipitation. In commercial practise the two techniques used employ either acid coagulation or rennet coagulation mechanisms. 

Although acid caseins are employed for a number of purposes, rennet caseins in which the protein remains associated with calcium and phosphate are preferred for plastics applications. Rennet is the dried extract of rennin, obtained from the inner lining of the fourth stomach of calves, and is a very powerful coagulant. As little as 0.2 parts per million are said to be sufficient to coagulate slightly acidic milk. Its coagulating power is destroyed at 100°C. 

In the rennet coagulation process fresh skimmed milk is adjusted to a pH of six and about 40 ounces of a 10% solution of rennet are added per 100 gallons of milk. The initial reaction temperature is about 35°C and this is subsequently raised to about 60°C. The coagulation appears to take place in two stages. Firstly the calcium caseinate is converted to the insoluble calcium paracaseinate and this then coagulates. 

Great care is essential in controlling the temperature and the coagulation process as otherwise impurities, particularly other proteins, will be brought down with the casein. Such impurities will adversely affect the transparency of the product. 

The condition of the curd on precipitation is important. As the milk starts to gel, agitators in the coagulation tanks are started as the temperature is raised to about 65°C. Under these conditions the protein is thrown out in fine particles. Too slow an agitation will produce large clots difficult to wash whilst too fine a curd also presents washing problems. In order to obtain the requisite consistency of the precipitate it may be necessary to add inorganic material to the skimmed milk. For example, the addition of phosphate ions will prevent undesirable flaky polymer. Similarly, calcium-deficient casein will not coagulate satisfactorily and the addition of calcium ions may be necessary. 

Calcium caseinate is produced from skim milk by adding an acid to cause the protein to coagulate, at which point it can be filtered to separate the curds from the whey. 

Caseins are used in wine making to clarify the wine by causing fine particles to coagulate with the protein so they can be easily filtered out or precipitated. 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

In the manufacture of articles direct from latex it is necessary to stabilise the latex (to prevent premature coagulation) by the addition of protective colloids such as casein soaps, gelatine and proprietary anionic surface active agents. 

The Daily Industiy. The first step in cheese manufacture is the coagulation of milk. Coagulation can be divided into two distinct phases, enzymatic and the non-enzymatic. In the primary enzymatic phase a proteol ic enzyme such as chymosin (rennet), or less effectively, pepsin, carries out an extremely specific and limited proteolysis, cleaving a phenylalanine-methionine bond of /c-casein, making the casein micelle metastabie. In the second, non-enzymatic phase, the... 

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