Rennet properties

O Brien, B., Mehra, R., Connolly, J.F., Harrington, D. 1999. Seasonal variation in the composition of Irish manufacturing and retail milks. 1. Chemical composition and renneting properties. Irish J. Agric. Food Res. 38, 53-64. 

Heat treatment of milk above 60 °C, which promotes whey protein denaturation and its complexation with K-casein at normal milk pH (6.6), also affects renneting properties. An increase in rennet coagulation time and a decrease in gel firmness were observed with increased heat treatment of milk (Menard and Gamier, 2005). Ultra-high temperature (UHT) treated milk failed to coagulate completely but the coagulation properties were restored by threefold concentration of the UHT milk (McMahon ef al., 1993). 

A significant effect of dietary starch content on milk protein content was observed, with slightly lower values P<0.0S) in milk from LS diet (3.73%) compared with those of the other two diets (3.77 and 3.79% in B and HF respectively). These differences did not affect the titratable acidity (on average 3.81 0.28 °SH/50 ml) and the renneting properties (clotting time 16.56 2.42 min curd finning rate 4.83 1.60 min curd firmness 33.62 6.51 mm). 

In conclusion our results confinn that high fermentable diets, if well balanced, do not alter digestive functions and animal health. Moreover they shghtly affect milk fat and protein contents furthermore, neither the milk acidification rate (although low), nor the renneting properties (always optimal) were modified by the different content of fermentable energy of the diets used in this trial. 

Property Rennet Lactic acid Sulfuric acid Cheese... 

Microbial rennets from a number of producers, eg. Novo Nordisk, Gist Brocades, and Miles, have been available since the 1970s and have proved satisfactory for the production of different kinds of cheese. Their price is considerably lower than that of chymosin. Their properties have proven very similar to those of chymosin (89,90), and only slight modifications of the traditional cheesemaking technique are required in practice. 

Table 30.1 Properties of rennet casein. Determined according BS1416 1961...

The principal component 1 (PCI) separated the acidification phases of BLG5, CREAM, BCAS, and MP clustered with negative values, from their rennet-induced coagulation phases that spread in a specific order associated with time from the left to the right of the map. These results showed that acidification and gelation of reconstituted milks induced different modifications in the fluorescence properties of Laurdan. 

The starting time for rheological measurements correspond to t = 120 min. Indeed, the rheological parameters were only recorded during the rennet-induced coagulation phase to avoid structural modifications during the acidification phase which may consequently influence the gelation process. Elastic and viscous properties of reconstituted milks... 

Casein may be coagulated and recovered as rennet casein by treatment of milk with selected proteinases (rennets). However, one of the caseins, K-casein, is hydrolysed during renneting and therefore the properties of rennet casein differ fundamentally from those of acid casein. Rennet casein, which contains the colloidal calcium phosphate of milk, is insoluble in water at pH 7 but can be dissolved by adding calcium sequestering agents, usually citrates or polyphosphates. It has desirable functional properties for certain food applications, e.g. in the production of cheese analogues. 

When heated in the presence of whey proteins, as in normal milk, K-casein and /Mactoglobulin interact to form a disulphide-linked complex which modifies many properties of the micelles, including rennet coagulability and heat stability. 

Removal of colloidal calcium phosphate (CCP) results in disintegration of the micelles into particles of mass 3 x 106 Da. The properties of the CCP-free system are very different from those of the normal milk system, e.g. it is sensitive to and precipitated by relatively low concentrations of Ca2 +, it is more stable to high temperatures, e.g. 140°C, and is not coagulable by rennets. Many of these properties can be restored, at least partially, by increased concentrations of calcium. 

Although CCP represents only about 6% of the dry weight of the casein micelle, it plays an essential role in its structure and properties and hence has major effects on the properties of milk it is the integrating factor in the casein micelle without it, milk is not coagulable by rennet and its heat and calcium stability properties are significantly altered. In fact, milk would be a totally different fluid without colloidal calcium phosphate. 

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

The strength of the rennet-induced gel is also adversely affected by heat treatment of the milk, again presumably because the whey protein-coated micelles are unable to participate properly in the gel network. Gels from severely heat-treated milk have poor syneresis properties, resulting in high-moisture cheese which does not ripen properly. Syneresis is undesirable in fermented milks, e.g. yoghurt, the milk for which is severely heat-treated (e.g. 90°C x 10 min) to reduce the risk of syneresis. 

The pH and the concentration of calcium in milk also vary, with consequential effects on the properties of renneted milk gels. The addition of CaCl2 to cheesemilk (0.02%) is widely practised and adjustment and standardization of milk pH by using the acidogen, gluconic acid-5-lactone (GDL), is recommended and commercially practised on a limited scale. 

Although the gelation properties of whey proteins are of great importance in many foods (Mulvihill, 1992) and it is possible to form a weak gel in creams by the formation of a continuous network of fat globules, most important milk gels are those involving casein micelles which can be made to form a gel matrix either by isoelectric precipitation (acid-induced gel) or by the action of a proteolytic enzyme (rennet-induced gel). Both gel types... 

Puhan, Z. 1969. Composition and properties of a rennet substitute from Bacillus subtilis. J. Dairy Sci. 52, 889-889. 

Penicillium caseicolum produces an extracellular aspartyl proteinase and a metalloproteinase with properties very similar to those of the extracellular enzymes produced by P roqueforti (Trieu-Cout and Gripon 1981 Trieu-Cout et al. 1982). Breakdown of casein in mold-ripened cheese results from the synergistic action of rennet and the proteases of lactic streptococci and penicillia (Desmazeaud and Gripon 1977). Peptidases of both lactic acid bacteria and penicillia contribute to formation of free amino acid and nonprotein nitrogen (Gripon et al. 1977). 

Green, M L., Marshall, R.J., Glover, F.A. 1983. Influence of homogenization of concentrated milks on the structure and properties of rennet curds. J. Dairy Res. 50, 341-348. 

Lucey, J.A., Tamehana, M., Singh, H., and Munro, P.A. (2000). Rheological properties of milk gels formed by a combination of rennet and glucono-delta-lactone. J. Dairy Sci. 67, 415 27. 

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