Heat-induced modifications in casein dispersions affecting their rennetability

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Abstract An alternative method to prevent microbiological problems occurring during cheese manufacture, such as late fermentation by spores from Clostridium tyrobutyricum, is to apply heat treatment of cheese milk. However, thermal inactivation of spore forming bacteria requires high or ultrahigh temperature heat treatment, which simultaneously causes whey protein denaturation and impedes rennet coagulation. A process strategy was designed to remove heat-sensitive whey proteins by diafiltration (microfiltration 0.1 μm) with ultrafiltration permeate. The resulting “whey protein-free” casein dispersion (3% casein, 0.02% whey protein) was heated to temperatures between 100°C and 140°C for up to 600 s before determination of renneting properties. The higher the heat load during thermal treatment the greater is the detected decrease in gel strength in casein dispersions despite the absence of whey proteins. Heat-induced changes in the calcium distribution between the micellar and serum phases were identified as the main factor impairing rennet coagulation. Formal kinetics were applied in order to predict a heating range, in which the casein dispersion shows a high rennetability and guarantees the inactivation of Clostridium tyrobutyricum spores by four log units. The experimental results were confirmed in a pilot-scale plant using UHT-heated “cheese milk” for cheese manufacturing.