Rennet gels

FIG. 26 Observed water self-diffusion coefficients as a function of the protein concentration (g protein/g water) for micellar casein dispersions ( ), for acid gels (O), and for rennet gels ( ) [reproduced with permission from Mariette et al (2002)]. 

Bulca, S., Leder, J., and Kulozik, U. (2004). Impact of UHT or high heat treatment on the rennet gel formation of skim milk with various whey protein contents. Milchwissenschaft 59, 590-593. 

Renneted gels Enzymatic action followed by precipitation by Ca +... 

Reduction of microorganisms in milk before cheese production must be achieved in such a way that the functionality of the milk proteins is not affected. Heat-resistant spores, such as Clostridium tyrobutyricum and C. sporogenes can cause severe spoilage of the cheese by late fermentation that can result in the production of H2 and CO2 gases, and unpleasant smelling fermentation products [102]. Although heat sterilization reduces these spores, because of the heat-induced complexation between 3-Lg and K-casein, UHT milk normally does not form a rennet gel and consequently could not be used efficiently for cheesemaking [87]. 

Milk gels can be made by the combined action of rennet and acid. With the combined action of acid and rennet, gels can be made over a broader pH and temperature range than by acidification alone, with both the pH and rermet action influencing the resulting gel properties (Roefs et al., 1990). 

Linearity between log B and log

casein gels. From the slope of the line, D can be calculated, and for acid gels, values between 2.35 and 2.4 are observed, in good agreement with simulation results. For rennet gels, the slope yields D = 2.2-2.25. 

Long-Term Rearrangement. This concerns changes after the gel has formed. Figure 17.16a shows that such changes occur in rennet gels, since the B value increases with time after gel formation. This can go along... 

FIGURE 17.16 Changes in rennet gels at various pH values (indicated) as a function of time after rennet addition, at 30°C. (a) Permeability B. (b) Endogenous syneresis pressure psyn. (After results by H. J. C. M. van den Bijgaart. Ph.D. thesis, Wageningen University, 1988.)... 

Brooker, B., Ferragut, V, Gill, A., and Needs, E. 1998. Properties of rennet gel formed from high-pressure treated milk. In K. Antio (Ed.), Proceedings of the VTT symposium, FreshNovel Foods by High Pressure, Helsinki, Finland, September 20-21,1998, pp. 55-61. 

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