Casein enzymatic coagulation

Enzymatic coagulation of milk. The enzymatic coagulation of milk involves modification of the casein micelles via limited proteolysis by selected proteinases, called rennets, followed by calcium-induced aggregation of the rennet-altered micelles ... 

Payens, T. A. J. 1978. On different modes of casein clotting the kinetics of enzymatic and non-enzymatic coagulation compared. Neth. Milk Dairy J. 32, 170-183. 

Ekstrand, B., Larsson-Raznikiewicz, M. and Perlman, C. 1980. Casein micelle size and composition related to the enzymatic coagulation process. Biochim. Biophys. Acta 630, 361-366. 

The physical and chemical characteristics of cheese curd depend on the method used to form the curd matrix. The curd is formed in basically one of two ways acid or enzymatic coagulation. In acid curd cheeses (cottage, baker s, cream), the curd is formed by direct addition of acid to the milk or by lactic acid produced by the fermentation of lactose. As the pH of the milk approaches the isoelectric point of casein (pH... 

The primary (enzymatic) phase of renneting overlaps somewhat with the secondary phase of aggregation. The gel subsequently undergoes syneresis to produce curds and whey while a slow but more general proteolysis of the caseins begins, which eventually contributes substantially to the distinctive flavor and texture of cheese. The enzymatic coagulation of milk and formation of the curd has been reviewed by Dalgleish (1987). Here, attention will be confined to parts of the subject that most clearly relate to the structure and stability of bovine casein micelles. 

Figure 19.3. Sketch of the enzymatic coagulation of casein based on the action of chymosin.

EEC regulation nr. 1725/79. Annex in, method L296/10. Quantitative analysis of skirtuned milk powder in feedingstuffs by enzymatic coagulation of casein. 

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... 

These are compounds obtained by chemical or enzymatic methods and are divided into primary and secondary derivatives, depending on the extent of change that has taken place. Primary derivatives are slightly modified and are insoluble in water rennet-coagulated casein is an example of a primary derivative. Secondary derivatives are more extensively changed and include proteoses, peptones, and peptides. The difference between these breakdown products is in size and solubility. All are soluble in water and... 

The expression transition refers to a change in physical state and, in a food, the transition of concern is often either from liquid to solid, solid to liquid, or solid to solid. It is caused primarily by a change in temperature (heating and/or cooling) or pressure (Roos, 1998). However, auxiliary conditions, such as pH and presence of divalent ions, as well as enzymatic action aid liquid to solid transitions. For example, gels can be created from Casein either by enzymatic action followed by precipitation with Ca + or by acid coagulation. 

Bringe NA and Kinsella JE. Eorces involved in the enzymatic and acidic coagulation of casein micelles. In Hudson BJF, Ed. Developments in Food Proteins, Vol. 5, Elsevier Applied Science Pubhshers, London, 1987, pp. 159-194. 

There are two principal established methods for the production of casein on an industrial scale isoelectric precipitation and enzymatic (rennet) coagulation. There are a number of comprehensive reviews on the subject (e.g. Muller, 1982 Fox, 1989 Mulvihill, 1992 Fox and Mulvihill, 1992) which should be consulted for references. 

The conversion of milk to cheese curd essentially involves coagulating the casein, either isoelectrically or enzymatically if present, the milk fat is occluded in the curd. The mechanisms of rennet and acid coagulation of casein and the subsequent manipulation of the coagula to produce cheese curd are described in the following sections. 

The rennet coagulation of milk is a two-stage process the primary phase involves the enzymatic production of para-casein and TCA-soluble peptides [(glyco) macropeptides] while the secondary phase involves the aggregation or gelation of para-casein Ca at temperatures >20°C the two stages overlap somewhat. The subject has been reviewed by Fox (1984) and Dal-gleish (1992, 1993). 

The coagulation of renneted micelles is very temperature-dependent (Gio 16) and normal bovine milk does not coagulate <18°C unless [Ca ] is increased. The marked difference between the temperature dependence of the enzymatic and nonenzymatic phases of rennet coagulation has been exploited in the study of the effect of various factors on rennet coagulation, in attempts to develop a system for the continuous production of cheese or casein curd and in the application of immobilized rennets. The very high dependence on temperature of rennet coagulation suggests that hydrophobic interactions play a major role. 

The K-casein provides a layer of hydrophilic polymer at the surface of the micelle that contributes to stability. Removal of the K-casein by enzymatic hydrolysis with chymosin (rennin) results in the micelles eventually undergoing coagulation. This is the principle of cheese making. 

Prodnction of yogurt and cheese involves destabilization of the milk emulsion with the assistance of microbial activity. In yogurt, the milk is coagulated and sonred by lactic acid produced by bacteria. Cheese making starts with an enzymatic modification of the casein micelles allowing them to co-precipitate with fat droplets, thus forming the cheese curd. 

Proteolysis has three phases (see Section 2.4.5.2.1) proteolysis in milk before cheese manufacture due to indigenous milk protease (plasmin) activity, the enzymatically induced coagulation of the milk in rennet cheeses (hydrolysis of K-casein by rennin) and proteolysis dining ripening of most cheeses, which is the most important reaction having a major impact on flavour and texture. 

---