Heat resistance of Lactobacillus paracasei isolated from semi-hard cheese made of pasteurised milk

Nine strains of non-starter Lactobacillus paracasei isolated from semi-hard cheese made of pasteurised milk were selected for their anticlostridial activity. Resistance to thermisation (60 °C, 5 min) and pasteurisation (73 °C, 15 s) was investigated using a submerged-coil apparatus. MRS broth-grown cultures of all nine strains survived thermisation in buffer. The level of resistance to thermisation was strain dependent and lower for freshly grown cells (stationary phase cells) than for resting cells (freshly grown cells kept diluted 10-fold in MRS broth at 17 °C for 6 days). None of the nine Lb. paracasei strains survived or recovered after pasteurisation in buffer when grown in MRS broth, while seven of the nine strains survived pasteurisation in UHT whole milk when grown in milk. Identity of the strains was successfully confirmed during the experiments using repetitive-PCR analysis. The potential of Lb. paracasei strains to survive pasteurisation of cheese milk was demonstrated.