Thermal inactivation of Bacillus cereus spores in micellar casein concentrates-effect of protein content and pH development

The spore count of micellar casein concentrate (MCC), an ingredient widely used in dairy processing, has to be reduced to increase the shelf life of intermediate and final dried products, and to guarantee the suitability for trade and export. A heat treatment of the concentrate prior to drying ensures low cell counts in the final product. However, it is not known whether spores are protected from inactivation in MCC, especially at high protein concentrations. Therefore, in this study, we examined the influence of the heating medium (water, whole milk, and MCC with 1.5%-14.3% protein) on water activity, buffering capacity, pH development during heating and Bacillus cereus IP5832 spore inactivation. With increasing protein content, the buffering capacity also increased. Water activity, pH drop during heating, and D values for the inactivation of B. cereus spores were not significantly different in all the media examined. Hence, the heat resistance of the spores was not affected by the protein content of the MCC. Also, the heat resistance in MCC was not different to the heat resistance in milk. Dairies can use the temperature-time combinations established for the heating of milk to design the processes aiming at the thermal treatment of MCC.