Rennet coagulation of milk

Effect of heat treatment on rennet coagulation of milk and related properties... 

Figure 10.3 Schematic representation of the rennet coagulation of milk, (a) Casein micelles with intact K-casein layer being attacked by chymosin (Q (b) micelles partially denuded of K-casein (c) extensively denuded micelles in the process of aggregation (d) release of macropeptides ( ) and changes in relative viscosity (0) during the course of rennet coagulation.

Measurement of rennet coagulation time. A number of principles are used to measure the rennet coagulability of milk or the activity of rennets most measure actual coagulation, i.e. combined first and second stages, but some specifically monitor the hydrolysis of K-casein. The most commonly used methods are described below. 

Figure 10.7 (a) Hot wire sensor for objectively measuring the rennet coagulation of milk, (b) Changes in the temperature of the hot wire during the course of the rennet coagulation of milk. 

Reuter, H. Hisserich, D. and Prokopek, D. 1981. Study on the formal kinetics of rennet coagulation of milk concentrated by ultrafiltration. Milchwissenschaft 36, 13-18. 

Rennet casein is produced from skim milk by treatment with certain proteolytic enzymes, known as rennets. The rennet coagulation of milk and related aspects are discussed in Chapter 10. Apart from the coagulation mechanism, the protocol for the production of rennet casein is essentially similar to that for acid casein. 

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). 

Severe heat treatments, especially >80°C, adversely affect the rennet coagulation of milk. Although changes in calcium phosphate equilibria are contributory factors, complexation of /3-lactoglobulin and/or ot-lactalbumin with x-casein via intermolecular disulfide bond formation is the principal factor responsible (see Fox, 1988). Most authors agree that the primary and, especially, the seconday (nonenzymatic) phase of rennet coagulation are adversely affected by severe heat treatments, as is the strength of the... 

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